Evaluation of natural materials in Sustainable Buildings: A …1587579/... · 2021. 8. 25. · DB HE Documento Básico de Ahorro de Energía (CTE) DB HS Documento Básico de Salubridad

IN DEGREE PROJECT MECHANICAL ENGINEERING,SECOND CYCLE, 30 CREDITS

, STOCKHOLM SWEDEN 2021

Evaluation of natural materials in Sustainable Buildings: A potential solution to the European 2050 long-term strategy.

VÍCTOR DE LAS HERAS REVERTE

KTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENT

Master of Science Thesis

Department of Energy Technology

KTH 2020

Evaluation of natural materials in Sustainable

Buildings: A potential solution to the

European 2050 long-term strategy.

TRITA: TRITA-ITM-EX 2021:299

Víctor de las Heras Reverte

Approved

2021-06-14

Examiner

Jaime Arias Hurtado

Supervisor

Jaime Arias Hurtado

Industrial Supervisor

Ximo Masip and Carlos Prades

Contact person

Ximo Masip


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Abstract Today, buildings consume 40% of total energy demand in the EU and are responsible for 36% of GHG emissions. For this reason, and due to the delicate situation of climate change that planet Earth is experiencing, solutions are being sought to make the building sector more sustainable. In the current project, the use of natural materials has been chosen as a solution in line with the EU 2050 long-term strategy. This research broadens the knowledge on sustainable building with natural materials as an alternative to conventional construction. To this end, first, an extensive state of the art has been carried out to gather information and identify research gaps on natural building materials and energy efficiency, proving the suitability of natural construction materials. Special emphasis has been put on straw bale construction and rammed earth construction, which have been studied individually. In addition, geometrically identical building models of both building techniques have been developed and simulated in Stockholm and Valencia in order to see how they would perform in different climates. Total energy demand for the straw-bale building of 140.22 kWh/(m2·year) in the case of Stockholm and 37.05 kWh/(m2·year) in the case of Valencia has been obtained. For the rammed earth building, a total demand of 301.82 kWh/(m2·year) has been obtained in Stockholm and 78.66 kWh/(m2·year) in Valencia. Once passive measures are applied in the different models, a reduction in demand for the straw bale building of 77.8% and 36.3% has been achieved for Stockholm and Valencia, respectively. In the rammed earth building, in contrast, the demand has been reduced by 86.3% in Stockholm and 73.9% in Valencia. Heat recovery ventilation and high insulation level have been identified as imperative needs in Stockholm, in contrast to Valencia. Other improvement strategies such as windows substitution, air permeability improvement, or natural ventilation for cooling have been implemented. Apart from that, better performance of the straw-bale buildings has been identified for both climates. Additionally, focusing on thermal inertia, its influence has been identified as not completely significant in terms of annual demand in the simulated climates.

Keywords

Straw-bale building, Rammed earth building, Sustainable construction, Natural Building Materials, Energy performance analysis, Energy performance optimization


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Acknowledgements First of all, I wish to give my sincere gratitude to my supervisor and examiner Jaime Arias Hurtado, a great

teacher and a great person, who has supported the project with his knowledge. Furthermore, I would like

to thank the guys from Catenerg, Ximo, and Carlos, and the whole team for their technical and motivational

support. I am also grateful for the assistance given by Joan, from Okambuva, whose knowledge about

bioconstruction has facilitated the definition of constructive characteristics.

Leaving aside the professional aspect, I would like especially to express my deepest gratefulness to my family

for trusting me during my whole student period and giving me this opportunity, which will change the

course of the rest of my life. To my sister Aida, I would like to give special mention to her for being a

“friend by blood”, who has brought to the world the most beautiful thing that my eyes have been able to

see in these difficult times, my nephew Dani.

Of course, my friends, from the first to the last, for the laughs, for the adventures, for the trips, for their

affection, for their unconditional support, and for being there even when they are not.

I dedicate this space to show my heartfelt and sincere gratitude to her, who in the hardest time of my life,

has been the one who has kept me going, fighting for my physical and mental health, and also my dreams.

Her name is Luci, and she is "home".


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Acronyms

BBR Boverket’s Building Regulations

BEST Building Energy Software Tool

BIM Building Information Modelling

CEB Compressed Earth Blocks

COP Conference of Parties

COP Coefficient of Performance

CSV Comma-Separated Values

CTE Spanish Technical Building Code

DB HE Documento Básico de Ahorro de Energía (CTE)

DB HS Documento Básico de Salubridad (CTE)

DNI Direct Normal Irradiation

EIFS Exterior Insulation Finishing System

EPBD Energy Performance Building Directive

EPDM Ethylene Propylene Diene Monomer

EPS Expanded Polystyrene

ESBA European Straw Building Association

ETICS External Thermal Insulation Composite System

EU European Union

FASBA Fachverband Strohballenbau Deutschland

GHG Greenhouse gases

GHI Global Horizontal Irradiation

GREB Ecology Research Group of la Baie

HRV Heat Recovery Ventilation

HVAC Heating Ventilating and Air Conditioning

IDF Intermediate Data Format

IEA International Energy Agency

IFC Industry Foundation Classes

IPCC Intergovernmental Panel on Climate Change

IPS Infinite Power System (ideal system)

ISH Integrated Surface Hourly

IWEC International Weather for Energy Calculations

LCA Life Cycle Assessment

LCC Life Cycle Cost

MEP Mechanical Electrical and Plumbing

NZEB Nearly Zero Energy Buildings

OSB Oriented Strand Board

PHI Passive House Institute

PP Polypropylene

PS Polystyrene

RFCP Réseau Français de la Construction Paille

SBUK Strawbale Building United Kingdom

UNFCCC United Nations Framework Convention on Climate Change

VOC Air Volatile Compound

XPS Extruded Polystyrene


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Table of Contents

1 Introduction .......................................................................................................................................................... 6

1.1 Background .................................................................................................................................................. 6

1.2 Purpose ......................................................................................................................................................... 7

1.3 Objectives ..................................................................................................................................................... 7

1.4 Methodology and Outline .......................................................................................................................... 7

1.5 Limitations ................................................................................................................................................... 8

1.6 Project contribution. ................................................................................................................................... 9

2 Literature Survey ................................................................................................................................................10

2.1 Energy efficiency .......................................................................................................................................10

2.2 Natural Building Materials .......................................................................................................................11

2.2.1 Straw-bale construction ..................................................................................................................12

2.2.2 Earthen construction .......................................................................................................................17

3 Building and Modelling .....................................................................................................................................20

3.1 Legislation ..................................................................................................................................................20

3.2 Design .........................................................................................................................................................20

3.3 Technical and Constructive characteristics ...........................................................................................22

3.4 Data acquisition .........................................................................................................................................23

3.5 Building modelling ....................................................................................................................................23

3.5.1 Software selection and description ................................................................................................24

3.5.2 Geometric modelling in IFC Builder ............................................................................................25

3.5.3 Energy modelling in Cypetherm EPlus ........................................................................................27

3.6 Energy simulation .....................................................................................................................................35

3.6.1 Climate Analysis ...............................................................................................................................35

4 Results and Discussion ......................................................................................................................................42

4.1 Energy simulation .....................................................................................................................................42

4.1.1 Straw-bale building ..........................................................................................................................42

4.1.2 Rammed earth building ...................................................................................................................47

4.2 Energy performance optimization – Measures ....................................................................................53

4.2.1 Straw-bale Building ..........................................................................................................................53


4.3 Energy performance optimization - Results .........................................................................................63

4.3.1 Straw-bale building ..........................................................................................................................63


4.4 Results Comparison ..................................................................................................................................69

4.4.1 Environmental and Economic assessment ..................................................................................71

5 Conclusions .........................................................................................................................................................74

5.1 Future work ................................................................................................................................................75

6 Bibliography ........................................................................................................................................................76


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1 Introduction

The current research study leads to a master thesis, in the Department of Energy Technology at the Royal

Institute of Technology (KTH). This master thesis is the result of the program Dual Master in Sustainable

Energy Engineering carried out in School of Industrial Engineering and Management (ITM) in KTH and,

in Escuela Técnica de Ingeniería Industrial (ETSII) in UPV. The current degree project is part of a larger

one in collaboration with the Cátedra de Transicción Energética Urbana (Catenerg) inside the Instituto de

Ingeniería Energética (IIE), a research institute belonging to UPV. In addition, this study was supported by

the Okambuva cooperative, which is a specialized construction company in the use of natural materials and

techniques for building.

This project is part of the research line on sustainable building with a focus on the use of natural materials,

especially in straw-bale construction. The aim is to investigate the energy performance of a building

constructed with different natural materials in different climates. In this case, two different climates have

been considered, corresponding to the locations of Valencia and Stockholm, and two geometrically identical

buildings, one built with straw as the main material, the other with earth.

The tasks would include (not limited to):

• Conducting an exhaustive and detailed literature survey on natural materials, especially on straw

and earth, and energy efficiency.

• Modelling a standard building through a Building Energy Simulation Tool.

• Energy simulations of the building in different climates and with different natural materials.

• Energy performance analysis of the building under different conditions.

• Energy optimization of the building for each scenario.

• Conclusions based on the comparison of the scenarios.

• Detailed report on the results obtained.

1.1 Background

Given the increase in greenhouse gas emissions in the building sector, both in the construction process and,

especially, in the energy use of buildings, which has become one of the sectors with the greatest room for

improvement, solutions have begun to be sought in order to reduce this excessive energy consumption and

these GHG emissions. This search for solutions is part of the EU's long-term strategy, which sets a 90%

emission reduction target for 2050.

Since the use of conventional material resources are limited, and in most cases, their production consumes

a large amount of energy, which leads to emissions of pollutants far above the requirements for

environmentally sustainable development, in recent years there has been a trend towards research and

application of natural materials in construction, which are more environmentally friendly. However, these

materials must comply with certain technical characteristics that allow their use in this sector: structural

resistance, fire resistance, acoustic insulation, acceptable lifetime, and most importantly, good thermal

properties that allow thermal comfort with the lowest possible energy consumption.

Two materials that meet many of the above-mentioned characteristics are straw from cereal crops and earth,

which are characterised mainly by their low carbon footprint and their thermal properties. Straw-bales have

low thermal conductivity, and earth has high thermal inertia. These two materials have been selected for

three reasons:

- They are gaining interest from the scientific community in recent years.

- To see the influence of thermal inertia and conductivity in different climates.

- They are materials that can be found almost everywhere.

A more detailed description can be found in Chapter 2, where a complete literature review is carried out.


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1.2 Purpose

The current master thesis is a continuation of a previous study, in which the calibration of a model of a

house built with straw was carried out by means of real in-situ temperature measurements, as well as its

energetic and environmental comparison with an equivalent house built with conventional materials

(concrete, steel...)[1], [2].

The purpose of the present project is to provide more knowledge about sustainable construction with

natural materials from the point of view of the energy performance of buildings. The thesis discusses the

possibility of using natural building materials to steer the building sector towards sustainable development.

To this end, the current work demonstrates that by using natural materials, such as straw or earth among

others, this would be possible, from a thermal performance perspective.

In addition, the project aims to provide information about the thermal properties of the materials studied,

as well as their performance in different climates, which would provide to the state of the art the techniques

to be used in each of the cases and their performance, with a view to the execution of a similar project.

Among the thermal properties of the materials, this study is mainly focused on the thermal conductivity and

inertia, assessing their influence on the buildings’ performance.

Given the lack of knowledge on this subject, and its scarce diffusion among professionals in the construction

sector, due in part to the lack of specific technical information on this type of materials, the current study,

following the line of research in the sector, aims to collaborate in this task.

1.3 Objectives

The present study aims to carry out a review of natural materials, especially straw and earth, with a special

focus on their thermal properties and in this way to see the thermal behaviour of buildings constructed with

these materials.

The main goal of the master thesis is to evaluate the energy performance of standard multi-storey buildings

constructed with straw and earth as main materials, respectively, in different climates. The results obtained

will show the differences between both materials and climates, analysing the energy performance in each

case. In addition, another objective is the energy optimization of the buildings according to the

corresponding climatic conditions. Thus, a standard can be generated to allow the optimisation of the

building according to the climate in which it is to be built.

The optimization criteria will be based on Passive House [3] standard. Therefore, as far as possible, buildings

will be optimised, depending on the climate, to meet the criteria set by the Passive House Institute (PHI).

Research questions:

• Are natural materials suitable for construction in terms of their technical characteristics and the

energy performance of the buildings in which they are used?

• What is the energy performance of two buildings, one built with straw bales and the other with

rammed earth, in different climates?

• What is the influence of thermal inertia on the energy performance of buildings constructed with

natural materials?

1.4 Methodology and Outline

Firstly, as an initial step, a literature review is done to present the current knowledge about natural materials

and energy efficiency in the building sector. This is an important part of the project, as it provides much

useful information about the issue and, especially about the straw and its characteristics in different technical

disciplines, since not such consolidated information is found in comparison to earth. In addition, from the

literature survey, the research gaps could be identified, which gives sense to the current project. In order to


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do this, bibliometric analysis has been done about natural building materials and sustainable construction

using Bibliometrix [4]. Once identified the research trends in recent years, more specific information was

searched and documented in this report.

After finishing the literature review and defining the project itself, data collection work takes place. In this

point, information related to the building typology, enclosures, layout, materials employed, activity, location,

weather, and others is gathered in order to use it afterwards in the building models.

The modelling process is carried out with a high level of accuracy to ensure the reliability of the simulations.

First, the geometrical model of the building is done based on the dimensions and layout defined including

windows. Then, the remaining data (enclosures, activity, thermal bridges…) are included in the model,

distinguishing between the straw-bale and the rammed earth building and between the climates, generating

different models with the same geometry. Once the models are finished, simulations are carried out.

Additionally, according to the results of the simulations obtained, the buildings are energetically optimised

by means of an iterative process of simulations, as well as parametric studies that speed up the optimisation

process. This is based on energy optimisation criteria according to the needs of the dwellings and the climatic

conditions of the location.

Results are analysed using graphs, numerical values, and tables, discussing them and drawing conclusions.

All this information about methodology and results is presented in this document, which follows the outline

below:

• Chapter 1- Introduction: In this chapter, different introductory sections are included, such as a short

background, the purpose and objectives of the project, the methodology, the limitations that could

affect the study, and the project contribution.

• Chapter 2 - Literature Survey: In this chapter, the complete literature review is presented, referring to

authors through references. It is divided into different sections: Energy efficiency and Natural

Building Materials These sections, at the same time, are divided into subsections. The aim is to give

a complete view of the state of the art in this area, focusing on straw-bale and earth construction.

• Chapter 3 - Building and Modelling: In chapter 3, the entire methodology related to the building and its

energy modelling is shown in a high level of detail. It is explained which values have been entered

into the software in such a way that the model can be reproduced unequivocally by anyone who

desires to do so.

• Chapter 4 - Results: Along with this chapter, simulation results are plotted and analysed.

• Chapter 5 - Conclusions: In this chapter, in relation to the purpose and objectives of the project, the

results obtained and the work accomplished, are discussed, and conclusions are drawn. In addition,

in this chapter, there is a section where future work is indicated to continue with the project once

the master thesis is finished.

1.5 Limitations

Mainly due to a lack of financial resources, the project has been carried out from a purely theoretical

standpoint. This means that the only resource used, apart from the bibliographic material accessed through

the university institutions, was a set of free computer applications and programmes. However, in this line,

it would have been interesting to carry out the actual construction of the buildings in the locations studied

so that the energy models could be calibrated and validated. This would probably have completely changed

the course of the master’s thesis. Nevertheless, this is not possible from an economic, legislative, and

temporal point of view.

Additionally, in order to broaden the work horizontally, and to have a better overview, more climates could

have been included in the work. This would have provided more information about the performance of

materials under different climatic conditions and the passive strategies to be taken accordingly. Initially, the


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simulation register would be extended to EU countries only, given the legislative constraints, but later on,

the horizon could be extended to other continents as well.

Apart from that, the investment costs of the buildings have not been budgeted as there is a lack of

information about the prices for materials, transportation, and construction labour. However, the annual

energy costs have been assessed. An environmental impact assessment of the whole life cycle of the

buildings has not been carried out either. Only CO2 emissions from the consumption of air conditioning

systems have been assessed.

Some factors could affect the results of the study that have not been taken into account:

• Buildings’ surroundings: In the project, no surroundings (mountains, trees, valleys, sea, other

buildings…) have been considered, which could have an influence on the results. Surroundings

could affect wind intensity and direction, shadows projected to the buildings. Also, the island effect

is not considered.

• Climate change: In the literature survey (Chapter 2), climate change has been identified as a factor

that could influence the energy performance of buildings in the coming years, since climate

conditions are being modified on the Earth. However, in the present project, the climate conditions

used for simulations are obtained from previous years’ records.

Other limitations:

• Software limitations: The simulation software has modelling limitations. The models have been

executed as close to reality as possible, but in certain aspects (ventilation, infiltrations, materials...)

simplifications have been made. There are also limitations in terms of simulations, where there are

certain restrictions.

1.6 Project contribution.

Given the importance of climate change and the contribution of buildings in this issue, this project is in line

with research into sustainable and environmentally friendly buildings. This study provides the energy

analysis and the energy optimization of buildings made up of straw bales and rammed earth as main

materials, which is performed in different climates (Stockholm and Valencia) to compare their performance

as substitutes to conventional construction. For this purpose, in the current project:

• A complete literature survey of natural building materials, with a special focus on straw, and energy

efficiency is included in order to gather the information and conclusions that other studies have

come with.

• As a result of the previous bibliographical review, literature gaps and future research opportunities

have been identified:

o Lack of information about specific environmental impacts, technical characteristics, and

energy performance of natural building materials.

o The need to replace conventional Portland cement sustainably and reliably, either by

modifying the production process or by replacing it entirely with natural materials.

• A better understanding and a wider knowledge about straw-bale as a building material are provided

to show the benefits of this bioclimatic construction technique in the building sector, focusing on

the thermal properties mainly.

• Different energy modelling of a standard multi-storey building, built with straw and earth

respectively, are done.

• Energy analysis of both natural building materials is performed in different climates, providing

knowledge about how climate conditions affect each construction technique.

• Energy optimization is done, supplying enhancement guidelines for the climates studied and the

natural materials employed. In this manner, the project provides a standard that could be taken as

a reference when designing a building in a location with climatic conditions similar to those studied.


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2 Literature Survey

According to the European Union (EU) [5], nearly 40% of the final energy consumption in the EU takes

place in buildings. Two-thirds of this energy is for space heating and cooling purposes. The residential sector

is not only the most energy-consuming sector but also the major responsibility of the CO2 emissions in the

EU with 36% of the global GHG emissions [6].

Directive 2012/27/EU [7] set different measures in order to achieve a 20% of reduction in energy

consumption by 2020. However, in 2018, in the framework of the Clean Energy for all Europeans package

[8], the new amending Directive 2018/2002/EU [9] on Energy Efficiency modifying the Directive

2012/27/EU, was agreed to update the normative and policy framework to 2030 and beyond. The most

relevant target in this Directive is to achieve an energy efficiency of 32.5% by 2030 which is established in

relation to the modelling projections in 2007 for the target year.

All this is in the line with the objectives fixed by the Paris Agreement on climate change following the

Conference of Parties (COP) to the UNFCCC [10], committing to limit the increase of the global average

temperature to 2ºC.

To achieve those objectives and knowing that there is much room for improvement in energy efficiency

concerning buildings (especially in the zone conditioning field), the construction sector proves to be a key

area for action. In terms of sustainability, not only the use and maintenance of the buildings are important,

but also the construction materials employed in the building. Zooming in, concerning the materials, their

origin is an important factor, but their manufacture and transport must be considered as well.

2.1 Energy efficiency

The energy demand in buildings, in the construction phase, in the use of the building throughout its life and

at the end of the building's life, is turned into a very significant economic expense and large amounts of

greenhouse effect gases emissions such as carbon dioxide, methane, nitrogen oxides, and other gases derived

from incomplete combustion of fossil fuels. Those pollutants are generated during the production of

electricity or for other purposes that contribute to the global warming in which the environment is being

involved today according to experimental research [11]. To mitigate this impact, the Energy Performance

Building Directive (EPBD) 2010/31/EU [12], had established that, for the year 2020, the new buildings

must have a nearly zero consumption in conjunction with other measures, in order to reduce the global

energy consumption and the greenhouse effect gases emission down to 20%. However, the EPDB

2010/31/EU [12] was modified by the EPDB 2018/844/EU [13], in which for the year 2050, it is intended

to reduce the greenhouse effect gases emissions between 80% and 95%, in comparison with the emissions

in 1990. This objective is set in the 2050 EU long-term strategy context [14].

Notwithstanding, as indicated by the International Energy Agency (IEA) [15] energy demand in buildings

is predicted to increase by 50% in 2050 in comparison to 2013 based on the current trends.

To reverse the situation, several strategies are being applied to minimize the energy consumption of the

buildings. Passive approaches try to reach this objective, focussing on different aspects such as the optimum

place of thermal insulation, air flow control, water vapour control, natural heating, cooling, and lightning

[16]. This is performed (referring to natural heating, cooling, and lightning) through strategies such as

defining the correct orientation or shadowing the openings and exterior walls in summer and taking

advantage of the solar radiation to warm the interior zones in winter.

Buildings’ performance is highly dependent on the climatic conditions in which they are located. For this

very reason, the adoption of the correct design of, especially, residential buildings, based on passive strategies

recommended for each climate, is a fundamental factor in terms of the energy efficiency of buildings [17].

Though the optimal passive design solution is dependent not only on the climate, but also on the building

activity and operation, topography, and landscape design. Even though the last three mentioned are not of

such importance, the building design has to take into account factors such as the occupation and the


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building’s intended use (residential, holiday residence, offices, sports facilities…). Additionally, the building

energy performance is also influenced by the surroundings, due to shadow casting, island effect, and wind,

among others.

Given the importance of climatic conditions, the design of a house should not only be based on average

values based on historical data but also consider trends and make an adaptive design. These trends refer

mainly to climate change, which is unfortunately uncertain. Despite the uncertainty that global warming

brings with it, there are records of temperature changes that can give an idea of future trends. The average

temperature in the EU territories in the decade 2002-2011 is 1.3°C higher than that of 1850-1899, according

to IPCC [18].

Turning to the particular case of Sweden, it is one of the European countries on which climate change will

have the greatest impact. Different climate scenarios show a temperature increase of between 2°C and 6°C

by the year 2100 (compared to the 1961-1990 historical average), with the sharpest changes occurring in

winter [19].

Climate change is a factor that could affect the energy use of the buildings and, also, their performance. For

this reason, the building passive measures must cover appropriate mitigation and adaptation measures to

deal with the climate change impacts [20]. In this line, different authors have evaluated the performance of

low-energy buildings under the shelter of different climatic contexts concerning cooling demand and

overheating in the residential sector [21]–[23].

In addition, climate adaptation measures have been analysed in order to study their effect on energy

performance: Thermal resistance, thermal mass, short-wave reflectivity, vegetated roofs, solar shading, and

natural ventilation [24].

Aiming to reduce the energy demand of heating and cooling systems of multi-unit residential buildings, the

most effective passive measures are, by importance order, the following: Overall enclosure U-Value, window

to wall ratio, window U-value and solar heat gain coefficient, window aperture, airtightness, shading, and

solar orientation [25]. Nevertheless, these most influential measures vary from one author to another

depending on the case study and on the selected criteria [16], [26]–[29].

2.2 Natural Building Materials

Apart from the energy consumption problem, the materials embodied energy has an important

environmental impact and, therefore, the carbon footprint of the conventional construction materials is

higher in comparison with organic materials [30], as in their manufacture important quantities of energy are

employed, and as a consequence, polluting gases are emitted to the atmosphere.

Natural materials represent a real alternative to conventional materials and, for that reason, part of the

research in the construction sector focuses on the search for suitable natural materials and their performance

as building materials. These materials have lower emissions of pollutant gases than conventional materials,

as concluded in numerous articles that study their environmental aspects [31]–[36].

With the aim of avoiding these emissions, not to have such an important carbon footprint attached to the

construction materials that are employed in modern architecture, the issue is to find sustainable materials

which are able to substitute them.

As a legacy of conventional construction, but safeguarding the environment, several authors [37]–[46], have

tried, with greater efforts in recent years, to carry out the substitution of a material with good technical

characteristics, such as cement, which has considerable environmental impacts. This has been done either

by searching for natural additives or waste to be incorporated into cement and modifying the cement

production process in order to reduce emissions, or by completely replacing the material with other more

sustainable materials. This has led to finding cement derivatives, but also natural materials that, in addition,

work as insulation such as hemp, jute and flax [47], wood waste [48], wool and coir fiber [49], cereal husks

[50], textile and paper [51] or straw. However, specific information about environmental impacts, technical


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characteristics, and energy performance is still lacking [31], [52], [53]. For these two reasons, the use of these

materials is not widespread and research on these aspects is still needed. The incorporation of natural

materials is understood not as a substitute but as a wider range of products [47].

Straw has been identified as one of the most suitable natural materials for construction. Straw-bales are

adequate for the building sector due to their thermal and physical properties, and due to the low

environmental impact attached. For that reason, an extensive literature review of straw-bale construction

(Section 2.2.1) has been done in the current project. In the literature review, it can be seen the numerous

advantages of straw-bale, especially in terms of thermal properties. However, straw bales lack high thermal

inertia, which could negatively influence the performance of the building. For this reason, the aim is to

identify whether this potential weakness is significant or, on the contrary, not an important factor in terms

of the energy efficiency of buildings. For this purpose, straw-bale construction has been compared with

rammed earth construction, which has higher thermal inertia but worse thermal characteristics. Earth is a

building material that has been deeply studied, and reliable information is available about it, in contrast to

straw. For this reason, the literature review about this construction technique (Section 2.2.2) is not as

extensive as in the case of straw bales.

Straw-bale construction and rammed earth construction are gaining increasing interest in European

countries [54], in addition to the growing publication of articles in the scientific community. Additionally,

these two materials are available almost anywhere in the world, making it very easy to carry out this type of

natural construction. For those reasons, apart from their physical properties and other aspects, straw and

earth have been chosen as the main focus of the current study.

2.2.1 Straw-bale construction

One solution that is emerging, is the construction of straw bales. Considering only the production and

construction phases, the embodied energy attached to a straw bale wall is about half of the value related to

a traditional wall and the CO2 equivalent emissions are smaller by more than 40% [55].

An example of an unfinished and finished straw-bale house can be seen in Figure 2.1.

Straw is a sustainable building material, what can be defined as a material that is harvested or produced, and

as a consequence, it can be used for construction not having such a negative impact on the environment as

it is a waste product of agriculture, that even allow the self-construction in determined cases [57]. As

indicated by the World Bank [58], more than 730,000,000 ha of cereals are cultivated worldwide, generating

1.5 kilograms of waste per kilogram of cereal, which are disposed or burned, usually, what could be used

for another purpose.

Straw as a material for construction has been used along with the human being history in a wide sort of

buildings, appearing in the 19th century with the invention of the baling machine [59]. Notwithstanding this,

in the mid-20th century, the straw bale construction was left behind due to the 2nd World War and the

expansion of Portland cement. Since the end of the 20th and the beginning of the 21st century, due to the

Figure 2.1 Example of an unfinished and finished straw-bale house [56].


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current environmental concern, straw bale (and other natural materials) buildings are reappearing in the

world as single-family homes, mainly [59], [57]. However, in the early stages of straw bale construction, most

of the constructions were self-built and not carried out by professionals as it was not very widespread at

that moment (the 1970s, oil crisis) [57].

It is remarkable the EU’s [60] relationship with this type of architecture with straw bales, as the Eco-

Innovation program has been created [61]. The EU contribution to this field could be seen in different

projects supported by this entity in which it is used straw as a construction material. For instance, in

Lithuania, Ecococon [62] is building houses with straw prefabricated panels [61]. Meanwhile, in Bradford

(England) it has been constructed a business park [63] with straw bales from Modcell [64] in concordance

with the Building Research Establishment Environmental Assessment Method [65]. The project in which

the EU is much more immersed is EUROCELL, providing half of the project budget (€1,611,096) [66].

This project falls back on Modcell [64] and the University of Bath [67].

Apart from those projects, the European Straw Building Association (ESBA) [68] is immersed in the

Interreg-Project UP Straw [69] which is an urban project with the main objective of up-scaling the use of

straw in construction for large-scale development of this natural material, for new construction buildings or

even for restoring edifications already built. The total budget of the project is about €6.3 million, but it is

granted by the EU with the 60% (€3.8 million) of the total amount of money needed, being the remaining

40% the percentage of the budget the quantity funded by other partners. The aim of this project is to reach

5% of the construction market in the year 2030, saving, in this way, 2 Mtons of CO2. Nowadays around

1,000 straw bale buildings are built every year along with the European territory, and the challenge for the

next years is to build 5,000 houses per year during the 2020s and around 50,000 every year during the 2030s.

In recent years, due to the growing interest in straw bale construction, different associations are emerging,

apart from ESBA, such as The Strawbale Building United Kingdom (SBUK) [70], the Fachverband

Strohballenbau Deutschland (FASBA) [71], the Réseau Français de la Construction Paille (RFCP) [72]. Also,

construction companies are appearing or are specialising in this kind of construction.

2.2.1.1 Construction techniques and requirements

Modern architecture use materials such as concrete or steel, that allow building with complex shapes, which

results in more difficulty with organic materials such as straw [59]. In addition, the physical properties of

straw bales present enormous variations depending on the composition of the straw, its orientation, and

disposition into the bale, the density, the content of water in it, etc (Table 2.1, Table 2.2 and Figure 2.2). So,

it is complicated to determine those properties and to construct a building without a standardized bale, from

the point of view of thermal analysis, structural calculations, and others.

Concerning the construction employing straw, there are different techniques in function on the structure

and support of the building. The bearing walls style is the traditional way of building dwellings with straw

bales, in which the straw is self-supporting [73]. Anyway, new technics are appearing such as “Post and

Beam” [74], GREB [75], modular cellulose [76], and mixed systems[74], [77], [78], in which the straw bales

are not self-supporting because other materials, like wood or steel, are employed. Those materials allow, in

this way, to build more sophisticated shapes and buildings with a higher number of floors. In addition, using

straw-wood modules allow penetration of this construction technique in the professional building industry

due to the potentially high level of standardization.

Additionally, straw bales can be used for the existing buildings' thermal envelope rehabilitation by means of

the Exterior Insulation Finishing System (EIFS) [79].

The usual dimensions of a straw bale are 37 x 47x 50-120 cm (High x Wide x Long) and the minimum

density is 80 kg/m3 and the maximum is generally over 150 kg/m3 in accordance with the capacities of the

new baling machines (nowadays, few buildings use bales with these high densities, for technical reasons)[80].

From a structural point of view, different studies have proved by means of stress tests that, straw bales for

construction must have a density between 90-130 kg/m3 [81]–[84].


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Concerning the fire resistance, considering the Standard Test Methods for Fire Tests of Building Construction

and Materials (ASTM E119-19) [85], straw bales resist combustion during 120 minutes [86]. Although it seems

counterintuitive, straw bales have adequate fire safety because, having a high density, the lack of air inside

them reduces largely combustion [87].

On the other hand, water is what should be taken into account, so straw must be protected from rain or

humidity, and, for that reason, the house must avoid water in its enclosures [59]. The water content could

lead to structural problems in the straw since, being an organic material, it degrades when the water

contained in the bale is high [88]. For this reason, it is recommended to perform a humidity test on the

straw bales before the construction phase. The water content must be below 18% in order to avoid this

problem since when it exceeds 25%, it starts to decompose [89].

2.2.1.2 Thermal properties

The behaviour of this type of materials in terms of their thermal properties was not deeply researched still

now. Even though there is reliable information about the thermal behaviour of insulating materials that are

used in modern architecture such as polystyrene (Extruded Polystyrene - XPS, Expanded Polystyrene -

EPS…) [90], information or data about straw bales thermal properties are not precise at all. This is due to

the fact that some variables influence the physical properties of straw as its origin, moisture, density, and

even the fiber and bale orientation once the house is built. Also, sometimes it is added plaster between bales,

and the presence of it in the bales changes the thermal properties, as well as the plaster type and thickness

[91]. Nevertheless, it is possible to find out articles related to the energy performance of the straw bales in

function of their characteristics (Table 2.1, Table 2.2, and Figure 2.2). The authors gathered in Table 2.1

have experimentally obtained some results. Also, they have tried to find a function to make a relation

between the thermal properties of straw and its density [57]. To get that information is essential to do an

energetic analysis, as it supposes an important factor in the energy performance of a building.

As thermal conductivity depends on several variables, it is hard to establish a correlation between it and the

straw bale density, but it is the most influential factor that affects the conductivity. For that reason, values

from different authors have been gathered in function of the density (Table 2.1, Table 2.2, and Figure 2.2).

In any case, it is verified that straw bales orientation on edge has better thermal properties from the point

of view of insulation than those placed on flat [57]. They got low conductivities, which are comparable to

the high-quality insulating materials that have been using today [90]. These good thermal properties make

the construction with sustainable materials take on more importance and interest because having insulating

characteristics it could be easier to build low-consuming houses, without using materials as XPS, EPS, etc.

which are not respectful with the environment since they come directly from oil [92].


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Table 2.1 Straw-bales properties in function of different characteristics [1]. 1/2.

Authors Origin of

Straw

Density

(kg/m³)

Thermal Conductivity (W/m·K)

Parallel Perpendicular Mean

Value

Munch-Andersen and

Andersen [93]

- 62 0.082 0.082

- 75 0.057 0.052 0.0545

- 81 - 0.057 0.057

- 90 0.06 0.056 0.058

- 90 0.05-0.06 0.05-0.06 0.055

- 100 - 0.038 0.038

- 150 0.06 0.048 0.054

A. Sabapathy [94] Rice 50-90 0.12-0.03 0.075

Lebed and Augaitis [95] - 80-190 0.00155+0.000357ρ+(3.381/ρ) 0.0748

Costes et al. [96] Wheat 68.1-122.7 0.0444+0.000272ρ 0.0703

Douzane et al. [97] - 80 0.067*(1+0.0078T) 0.046*(1+0.009T) 0.0682

Palumbo et al. [98] Barley

(81%) 107.5 0.037+0.019*%HR 0.0399

Vėjelienė [99] - 50-120 0.10312-

0.00036ρ+0.0000175ρ²

0.09637-

0.001460ρ+0.0000107ρ² 0.1243

Ashour [100] Wheat 82-138 0.0399-0.00023ρ+0.00269T 0.0819

Barley 68-98 0.0625-0.0005ρ+0.002237T 0.0769

ITeCons [101] Rice 78.7-83.3 - - 0.0409

McCabe [102] Wheat-

Rice 130 0.0605 0.0487 0.0546

Shea et al. [67] Wheat

90 0.06 0.056 0.058

63 - - 0.0594

76 - - 0.0621

85 - - 0.0619

107 - - 0.0642

114 - - 0.0642

123 - - 0.0636

Saini et al. [103] - 90-110 - - 0.045

Douzane et al. [97] - 80 0.072 0.051 0.0615

Conti [104] - 75 0.066 - 0.066

Grelat [105] - 77 0.066 - 0.066

Marques et al. [106] Rice 80 - - 0.0393

100 - - 0.0392


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Table 2.2 Straw-bales properties in function of different characteristics [1]. 2/2.

Authors Origin of

Straw

Density

(kg/m³)

Thermal Conductivity (W/m·K)

Parallel Perpendicular Mean

Value

Cascone et al. [107] Wheat 78 - - 0.0573

Cascone et al. [108] Wheat

200 - - 0.06

250 - - 0.07

300 - - 0.075

350 - - 0.08

Gallegos-Ortega et al.

[109] Wheat 115 - - 0.0939

Zhang et al. [110] Wheat - - - 0.074

D’Alessandro et al. [59] Wheat 80 - - 0.052

Wei et al. [111] Rice 250 0.051-0.053 0.052

Goodhew and Griffiths

[112] Rice 60-90 0.07-0.09 0.08

Buratti et al. [113] - 105.69 - - 0.065

Brzyski et al. [114] Rye 50.9 - - 0.0473

Evola [115] Wheat 75 - - 0.069

Drozd et al. [116] - - - - 0.08

Seitz et al. [117]

Barley

89.5 - 0.11-0.17 0.14

90.1 - 0.11-0.16 0.135

89.6 - 0.08-0.17 0.125

Spelt 131 - 0.14-0.17 0.155

Wheat

291 0.15-0.21 0.18

333 0.14-0.15 0.145

372 0.20-0.25 0.225

Figure 2.2. Thermal conductivity of straw bales in function of its origin and density [1].

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400

Co

nd

uct

ivit

y (

W/m

K)

Density (kg/m3)

Unknown

Wheat

Rice

Barley


-17-

As it could be seen in Figure 2.2, the higher it is the density of the straw, the higher it is the thermal

conductivity, ranging from 0.04 to 0.23 W/(m K). However, as said before, rarely, straw bales with a density

value over 150 kg/m3 are employed, so it is not possible to find buildings with large conductivities in the

straw bale walls, for thermal purposes, mainly.

To make a point, one disadvantage regarding the thermal properties is that straw bales are lightweight or, in

other words, it has low inertia, what could lead to overheating in the summer months [118].

Apart from the beneficial thermal properties, straw bales also have good acoustic properties, that could even

be improved by the utilization of mortars [119]. In comparison with conventional insulating material, such

as EPS, straw bales work better in terms of soundproofing [107].

2.2.1.3 Life cycle assessment (LCA)

From a life cycle perspective, using straw bales for construction, it is achieved high net carbon storage since

it is an agricultural waste that is rejoined to the cycle by integrating it into the building. In that way, it is

being substituted with other conventional materials, such as concrete, which have an important

environmental impact [30]. In addition, in some places, the straw is burned, as it is the easiest and cheapest

way of removing a large amount of straw, which has negative effects on the environment [120], [121].

Therefore, using it for construction, the problems associated with burning are avoided, as well.

Concerning the durability of these buildings, their expected lifetime could be more than 100 years. As a

reference, the oldest known straw bale house that still exists was built in 1903 in Nebraska (Burke house)

[74].

The standardized way to evaluate the life cycle environmental impacts of a product (in this case, the straw)

is a Life Cycle Assessment (LCA). This method considers all the aspects of the product use and

environmental releases from when it is produced to the disposal or recycling at the end of life [122]. When

straw bales are used to a greater or lesser extent in a dwelling, the building embodied energy is lower than

those that are built with only conventional materials [123].

A. Chaussinand [57] has researched the impacts of the construction of a straw bale building in Switzerland,

considering a life cycle of 60 years, obtaining a reduction of 50% in the environmental impact. A. González

[124] researched, in addition, about what is known as the embodied energy and carbon of straw in the

Andean Patagonia. In this study, they came up to the conclusion that it exists high non-renewable energy

inputs due to the farming and transports that make the sustainability of the straw-clay blocks worse than

what was supposed beforehand. Nevertheless, the energy attached to straw bales or straw-clay blocks to

build 1 m2 of the wall has been estimated to about 28 MJ and 40 MJ respectively [30]. This supposes a small

environmental impact if it is compared with buildings made up of bricks, in which the total energy required

to construct the same wall surface is about 488 MJ/m2, or concrete, whose embodied energy is

approximately 169 MJ/m2 [30]. Furthermore, the straw bales have, per unit, the primary energy content of

105 MJ, and greenhouse effect gases emissions of −50 kg CO2 equivalent [125]. Also, an LCA of different

buildings was made in order to analyse the consequences of making a combination between biomaterials

and technologies, and they concluded that straw bales insulation reduces the emission of 1,23 kg of CO2

equivalent each year [126].

Moreover, regarding carbon sequestration, straw absorbs CO2 during the growing process of the plant

thanks to photosynthesis. As it is studied, 1 kg of straw can sequester, during its growth, about 1.34 - 1.35

kg of CO2 [127].

2.2.2 Earthen construction

Especially in the last decade, the earth, as a building material, has received great attention from the scientific

community [128]. However, according to different authors [129]–[131], the earth started to be used for

construction from 9,000 to 14,000 years ago. There are several examples throughout history of earthen

constructions, such as extensive sections of the Great Wall of China, built 3000 years ago [128], the Huryuji


-18-

Temple in Japan (1300 years ago), rammed earth buildings in the Himalayan region constructed in XII

century [132], and the city of Shibam in Yemen, which has buildings up to 10 floors (100 years ago) [133],

among others. Nowadays, it is estimated that at least 30% of the world’s population lives in earth buildings

(including all types of construction techniques), with predominance in underdeveloped countries.

Different earth building techniques are well established in the construction sector, such as wattle and daub

[134], cob [135], rammed earth (including earth projection) [136], [137], earth bricks (adobe) [138] or

compressed earth blocks (CEB) [139]. An example of a rammed earth building can be seen in Figure 2.3.

Figure 2.3 Example of a rammed earth house [140].

Earth, like other natural building materials, has low embodied energy and low carbon dioxide emissions

[128]. The energy required to manufacture materials is an important aspect concerning the environmental

impact of a product [141]. Thus, choosing the correct building materials is key for an adequate life cycle of

the building. Earth is a material that can be found almost everywhere, so transport is not either a problem.

As for the physical properties, earth construction is suitable for building. However, the soil must undergo a

stabilisation process to improve its physical properties. In this way, the plasticity of the soil is reduced and

its performance under compressive stress is improved. This stabilisation can be carried out by lime, cement

[142], cow-dung, and saw dust (adobe bricks) [143]. In some cases, to improve the thermal properties of the

soil, straw is added to the mixture, but this reduces its compressive strength [144]. Compacted soil is

considered suitable for construction when the compressive strength exceeds 2 MPa [142]. Unfortunately,

earth constructions alone are not suitable in regions with seismic movements, so the use of a reinforced

concrete structure is necessary [145], [146]. In addition, earth, as a building material, is less durable than

conventional materials. Thus, this construction with compacted earth has structural limitations and needs

high maintenance [147]. Apart from that, this type of construction needs high wall thickness, up to 40-50

cm. Concerning sound insulation, a 36-63 cm thick earth wall has a sound reduction index of 46 dB - 57

dB, which is a good value compared to other materials [148].

The air quality is another positive point of earth buildings. First, this type of construction is not associated

with the production of air volatile compounds (VOCs), which could damage the tenants’ health.

Additionally, the earth walls are capable of absorbing moisture from the air [149]–[151], controlling in that

way the humidity in the living spaces and, consequently, improving the comfort conditions inside the

building. Hence, the relative humidity of the building can be maintained between 40% and 60% [148], which


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ensures ideal air humidity conditions, which, together with a good temperature, provides perfect thermal

comfort.

Finally, according to some authors [152], [153], earth thermal properties are adequate for construction.

Notwithstanding, thermal insulation is not one of the most interesting features of earth, which has a

conductivity of around 1.5 W/(m·K). Therefore, the most interesting characteristic, from a thermal point

of view, is inertia, which is the capability to store the energy in the walls, delaying the heat wave. However,

further investigations about inertia and its advantages are still needed [154], [149].


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3 Building and Modelling

During this chapter, information about legislation considered and about the building characteristics is

shown. In addition, the entire modelling process is explained in detail, so that it can be perfectly reproduced

by anyone who wishes to do so.

3.1 Legislation

In the present project, the relevant European and national building regulations have to be complied with,

so that the buildings studied could be implemented at a more advanced stage of this project if desired.

Since the EPBD 2010/31/EU [12] came into force in May 2010, the definition of Nearly Zero Energy

Buildings (NZEB) was established, which are buildings with high energy efficiency, and whose demand has

to be met by renewable sources [155]. The EPBD established the NZEB requirement for all new buildings

by the end of 2020. Thus, from now on, all new buildings must comply with this regulation.

Concerning the national building regulations, each country has its own normative (based on the European

one), which sets out the requirements for buildings. In Spain, the Technical Building Code (CTE-2019)

[156] is the one that applies in the Spanish territory, being the Basic Document on Energy Saving (DB HE)

[157] which establishes the requirements in energy terms. In Sweden, Boverket’s Building Regulations (BBR-

2018)[158] is normative in force for buildings. Due to the discrepancies between the different national

regulations regarding NZEB, an alternative demand criterion has been used for the project. In this case,

Passive House [3] certification has been chosen as it is restrictive. Passive House is a certification created by

the Passive House Institute, which establishes the following criteria to be fulfilled:

- Maximum Cooling Demand: 15 kWh/(year·m2)

- Maximum Heating Demand: 15 kWh/(year·m2)

- Maximum Air Infiltrations (Pressure difference 50Pa): 0.6 ren/h

Since buildings in different climates must be comparable, the European standard EN 16798-1:2019 [159] is

employed in the current project to define the activity conditions (occupancy, lighting...) of the building.

3.2 Design

One of the characteristics that define the final design of the building is its location. However, the aim of

this project, Section 1.3, is to carry out the energy analysis of the same design in different climates.

For this reason, the Building archive of the IEA [160] for the validation tests is employed. This building file

contains the plans of 6 different building typologies, where buildings 1 and 2 correspond to single-family

dwellings and buildings 3, 4, 5, and 6 to multi-storey blocks of flats with independent dwellings. From an

energy transition perspective, urban areas result in the main influent, where multi-storey blocks predominate

over single-family dwellings. Thus, the two first typologies have been discarded.

Since the purpose is to model only one geometric model, it has been decided to select building 4, which is

five floors building. All the floors are simple and identical, and 2.7 m high each. In Figure 3.1, the plans

corresponding to the selected building are shown, where geometry and dimensions are detailed:


-21-

Figure 3.1: Floor plan of the building. Geometry and zoning [161].

As can be seen in Figure 3.1, the building under study has a total of 21 independent zones per floor. These

zones correspond to 4 independent dwellings and a common area (Corridor - E11). This layout is repeated

identically on all floors of the building. The dimensions of both the spaces and the glazed surfaces are

indicated in Figure 3.1. Finally, the orientation of the building is also indicated by means of an arrow.

Table 3.1 shows the zoning of the building with the calculation of surface area and volume, considering a

useful height of the spaces of approximately 2.5 meters. The total private surface amounts to 1113.25 m2.

Table 3.1: Space zoning of the building. Surface and volume calculation.

Zone code Zone name Surface (m2) Volume (m3)

E11 Corridor 26.88 67.2

E8 Lobby 4 10

E7 Single room 10.73 26.82

E2 Bathroom 3.42 8.55

E3 Double room 17.05 42.62

E1 Living-Dining-Kitchen 27.86 69.65

Total Surface (1 dwelling + Corridor) 63.06 157.65


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3.3 Technical and Constructive characteristics

The buildings have been modelled according to bioclimatic architecture and green building principles. On

the one hand, materials with good thermal properties, such as straw or earth, have been considered in order

to achieve low energy consumption and maximize comfort inside the building; on the other hand, the use

of such materials implies a responsible use of existing resources, favouring sustainability in construction. In

this section, the technical and constructive characteristics of both buildings (straw-bale and earth buildings)

are detailed. Both buildings share identical technical descriptions for the ground floor and the internal floor

slabs, but different materials are employed for the remaining enclosures. Windows are identical in both

buildings as well.

As for the technical characteristics, the floor would be executed with 80 mm thick wood fiberboards (Steico

floor [162]) supported on a structure of timber and oriented strand board (OSB) panels, in accordance with

the construction cooperative Okambuva [163]. In contact with the basement, the floor has a breathable

layer, to avoid condensation or humidity in the structure. And finally, it is finished with pine wood flooring

as the last layer.

The other enclosure shared by both buildings is the interior floor slab, which is made up of a framework of

beams at the structural level followed by a 2 cm pine boarding. In addition, a layer of expanded polystyrene

(EPS) is added as soundproofing. Wood fiber insulation is placed as an internal layer, followed by oriented

strand board (OSB), and finished with pine wood decking on top.

Finally, the windows are composed of a wooden frame with double glazing and an air chamber (U= 2.9

W/m2 K) [164], and a solar heat gain coefficient of 0.5. The heat transfer coefficient of the carpentry is 3.2

W/m2 K. The main door is made of solid pine wood.

From now on, a distinction is made between the enclosures that are different in the straw-bale building and

the rammed earth building:

• Straw-bale building

The vertical building envelope consists of 25 cm thick prefabricated modules of rice straw and wood placed

on the wall perpendicular to the heat flow. Straw is compressed with a relative humidity of <15%. In this

project, a density of 120 kg/m3 has been selected for the straw bales, therefore, taking the trend line as a

reference, the conductivity chosen is 0.067 W/(m K). The structural sawn timber of the prefabricated

modules has the mechanical classification C24 according to the European Standard UNE-EN14081 [165]

and its dimensions are 100x150 mm. The prefabricated modules are externally covered with 22 mm thick

multi-thermal wooden panels, placed on horizontal and vertical wooden supports. Walls are lightly

ventilated by means of an air chamber of 25 mm. In addition, the interior walls would be completely

plastered with clay.

Internal partitions are made up of a 10 cm straw layer and with OSB at both sides. This configuration

insulates each private dwelling to the common zones that are not air-conditioned.

The straw-bale building roof consists of a double roof system; the lower horizontal roof, supported on the

straw-bale modules. The roof insulation consists of 25 cm thick straw-bale, identical to those placed in the

external walls, supported by a timber beam framework and OSB panels. The upper roof is placed over an

air chamber where the beams are located. The external roof is executed by means of sand and gravel, over

an Ethylene Propylene Diene Monomer (EPDM) layer. However, to simplify the modelling, not all the roof

layers are going to be added, since some of them are not relevant, from an energy performance perspective,

such as the beams.

• Rammed earth building

The external wall of the rammed earth building is the most distinctive enclosure of the building. The vertical

envelope of the building is made of compacted earth only. For the construction of these walls, a framework

would be used to allow the compaction of the moist earth (rammed earth construction). Once compacted,


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the framework would be removed, leaving only the earth wall. Typically, in this type of earth construction,

a layer of insulation is added, either inside the wall or as an external thermal insulation composite system

(ETICS) 4-5 cm thick. However, since this project aims to compare natural materials on equal terms, no

extra insulation layer will be added to the initial building. The wall thickness is 45 cm, which is an average

value for this type of construction. As for the thermal characteristics of the compacted earth, it has a

conductivity of 1.5 W/(m·K), which is high compared to the conductivity of straw. However, it has a

density of 1,855 kg/(m3) and a specific heat of 2,085 J/(kg·K), which results in higher thermal inertia.

As for the internal partitions, compacted earth with identical characteristics is used, but this on this occasion

with a thickness of 15 cm. This simple configuration is used both for the separation between the different

areas of the house, as well as for the separation with other dwellings or common areas.

In keeping with the constructive characteristics of the rammed earth building, the roof of the building is a

green roof, which has the following technical characteristics. Firstly, an exposed truss of timber beams

serves as the roof structure, followed by a pine planking. As for the vegetated roof, it comprises two

geotextile protection sheets, a waterproof layer, drainage nodules layer, low-density earth layer (vegetable

substrate of 30 cm thick), and plants. As in the straw-bale building, in order to simplify the model, some

roof layers are discarded for the simulation, but only those that are not significant from a thermal point of

view.

3.4 Data acquisition

First of all, in order to develop a reliable model, all the necessary information must be obtained, as accurate

as possible to reality. To this end, different sources of information have been used depending on the data

required.

As regards the provenance of the building geometry, this has been specified in the previous Section 3.2,

being the Building archive of the IEA [160]. In this case, it has been obtained from the Ministry for

Ecological Transition and the Demographic Challenge, through the Secretary of State for Energy [166].

Regarding the materials used in the house, they are mainly based on the bioclimatic construction techniques

used by the cooperative Okambuva [163]. The constructive characteristics of the building are detailed

according to previous buildings made by the cooperative, mainly. In addition, the cross-sections of each of

the enclosures have been supervised by Okambuva architects for both, the earthen and the straw-bale

buildings.

Finally, concerning the weather files, it has been decided to use the ASHRAE International Weather for

Energy Calculation (IWEC) [167]. IWEC are “typical” weather files, available for different locations around

the world, which are suitable for building energy simulation programs as they are available in .epw (Energy

Plus Weather). The files are obtained from Integrated Surface Hourly (ISH) weather data, originally gathered

at the National Climatic Data Center [168]. Those files contain valuable information for the energy

calculation, as a result of at least 12 years of records up to 25 years.

The rest of the parameters, related to the modelling of the building, such as building activity, thermal bridges,

or other elements such as glazed openings, are detailed in section 3.5.

3.5 Building modelling

The first step, with the final purpose of doing an energy analysis, is to elaborate the house model in 3

dimensions with a specific software specialized in the calculation of thermal loads. Working outwards from

there, the execution of the model is needed to obtain a simulation of its performance and analyse the values

obtained. In this project, the software selected to carry out the energy simulations is Cypetherm EPlus [169].


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3.5.1 Software selection and description

Cypetherm EPlus is a simulation software used for the calculation of the energy performance of the

buildings based on the thermal loads by means of a building model created for the energy simulation, which

uses EnergyPlus [170] as the calculation engine.

There is a great quantity of Building Energy Software Tools (BESTs) [171] that allow this kind of

simulations, in an energetic way, of buildings’ performance such as the ones studied in this project. In

addition, different simulation applications use EnergyPlus as the simulation engine, although they use a

different interface and usability.

In this case, Cypetherm EPlus has been selected taking advantage that it is possible to obtain it for free by

means of the academic licence, and because of its intuitive operation and manageability. In comparison to

other applications, Cypetherm Eplus has the main advantage of working with Building Information

Modelling (BIM), which is explained in this section. Therefore, in case of further exploration in areas other

than energy at a later stage of the project, it is one of the few that would allow it. This application has been

chosen among other BESTs intended for the modelling of buildings and the simulation and calculation of

the thermal loads (DesignBuilder [172], Cypetherm HE Plus [173], IDA Indoor Climate and Energy (IDA

ICE) [174], etc.).

Figure 3.2 Open BIM workflow flowchart portrait [175].


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Cypetherm EPlus is integrated into the Open BIM workflow through the Industry Foundation Classes (IFC)

standard (Figure 3.2). Using Open BIM, it is possible to establish a collaborative, multidisciplinary workflow

(energy simulations, HVAC, MEP, structure, fire protection, plumbing, telecommunications, electricity,

acoustic simulations, etc.), which allows building projects to be carried out in an open, coordinated, and

simultaneous approach among the different professionals involved in such projects.

The main advantage of this technology is that it is based on open and public standard interchange formats

(IFC). For that reason, the information gathered in the BIM project is not linked to any of the applications

that take part in it. The IFC, defined by ISO 16739-1:2018 [176], are an open international standard for

Building Information Model (BIM) data sharing in the construction and facility management industries.

The stages in the workflow are the following, according to Figure 3.2:

- Beginning of the BIM project

- Use of the specialized application (in this case Cypetherm EPlus)

- BIM model update in Cypetherm EPlus

- Export of IFC file to BIM Project

- Consolidation of the BIM Project

- Results and export of technical documents.

To carry out the model process, firstly, it is necessary to draw the different enclosures, defining their

thickness, and define the type of precincts existing in the house in IFC Builder [177]. IFC Builder is the

application where the 3D model is created and the IFC file is imported to Cypetherm EPlus. However,

once the model has been imported to the simulation software, it can be updated anytime when any change

has occurred in IFC Builder, without losing the information added in Cypetherm EPlus, provided that the

changes are compatible with the previous model. On the other hand, this characteristic allows, thanks to

Open BIM, to share the project in order to work at the same time in different aspects of the project, if

needed, as the basic building is modelled only in IFC Builder, and it can be imported in each specialized

application. Then, in the specialized application, Cypetherm EPlus, the remaining data are defined, and the

simulation is performed.

3.5.2 Geometric modelling in IFC Builder

As mentioned above, it is necessary to define the shape of the building and the dimensions of all the

enclosures to generate the structural characteristics of the building to be exported to BIMServer, and finally

imported into Cypetherm EPlus.

Firstly, to extrude the building in the software, it is convenient to use a DXF file of the building plan (created

in AutoCAD [178]), which allows the building to be accurately drawn and extruded in IFC Builder. This

DXF file can be imported into IFC Builder as a template and can be assigned to the different floors as

required.

Once the template has been entered into the program, the enclosures can be precisely defined, but first, the

different floors must be determined. It is essential to know how the floors are set up in this programme, in

order to be able to define them all properly. Each floor includes the contents of the space between the top

of the floor and the top of the interior floor slab, which is shared with the next floor, or even the top of the

roof if the highest floor is the one being defined. Thus, while selecting the floor height, consideration should

be given to the fact that the thickness of the lower floor slab does not affect the air space, but the upper

inner floor slab does, since the floors are defined from floor to floor. Thus, the various floors have been

established as follows:


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Figure 3.3 Building floors definition in IFC Builder.

As it could be seen in Figure 3.3, floors from 1 to 4 have been defined jointly as they are identical, while the

roof and the ground floor have been created separately. Taking into account that the height of each floor is

2.7 meters, the total height of the building amounts to 13.5 meters.

Once the floors have been generated, the different enclosures and elements are geometrically created in IFC

Builder according to the plans imported. Other aspects, such as enclosures' thicknesses, orientation, and

shadows are defined here.

Figure 3.4 3D view of the building in IFC Builder.

In Figure 3.4 a three-dimensional view of the building could be observed. The finished geometrical model

must be exported for further use in Cypetherm EPlus.


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3.5.3 Energy modelling in Cypetherm EPlus

Once the project is imported in Cypetherm EPlus, the modelling referred to materials, activity (occupation,

equipment, lightning, ventilation…), location, climate conditions, thermal bridges, HVAC systems, and

others take place.

In order to compare the straw-bale building in different climates, several assumptions and simplifications

have been considered the same way in all of them. The assumptions and inputs are going to be categorized

by their nature.

3.5.3.1 Materials

In Section 3.3, the building constructive characteristics are detailed. However, concerning the model, some

simplifications have been considered in order to facilitate the modelling process without compromising the

quality of the results.

As for the windows, in the initial model, they have been established as old double-glazed with an air gap

between glass. The approximate heat transfer coefficient of this type of window is 2.9 W/(m ·K) [164]. The

solar heat gain coefficient set in the initial models, for the windows, is 0.5. Concerning the carpentry, it is

made up of wood, covering 13% of the opening. The heat transfer coefficient of the opaque material is 3.2

W/(m ·K) and absorptance of 0.6. No extra accessories or shading elements have been considered in the

initial model.

Regarding the opaque elements, firstly the enclosures shared by the straw-bale building and the earth

building (Slab-on-ground floor and Internal floor slab) will be detailed, and then the particular enclosures

of both buildings respectively. The different layers and their respective properties are detailed below (from

Table 3.2 to Table 3.9), and the U-Value of the different enclosures is presented in Table 3.10.

Table 3.2 Layers’ characteristics and thermal properties. Floor.

Layers Thickness

(cm) Conductivity (W/(m·K))

Thermal resistance ((m²·K)/W)

Density (kg/m³)

Specific heat (J/(kg·K))

Pine wood C24 2.2 0.13 0.17 420 1600

Waterproof & Breathable sheet

0.2 0.22 0.01 910 1800

Oriented strand board [OSB]

2.2 0.13 0.17 650 1700

Floor insulation 8 0.038 2.11 160 1000

Pine Wood C24 2.2 0.13 0.17 420 1600

Waterproof & Breathable sheet

0.2 0.22 0.01 910 1800

Table 3.3 Layers’ characteristics and thermal properties. Internal Floor Slab.

Layers Thickness



Density (kg/m³)


Pine Wood C24 2 0.13 0.15 420 1600


2.2 0.13 0.17 650 1700

Wood Fiber insulation

3 0.031 0.97 40 1000

Expanded polystyrene [EPS]

0.3 0.029 0.1 30 1000

Pine Wood C24 2 0.13 0.15 420 1600


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• Straw-bale building

Table 3.4 Layers’ characteristics and thermal properties. External wall. Straw-bale building.

Layers Thickness



Density (kg/m³)


Pine Wood C24 3 0.13 0.23 420 1600

Air Gap 2.5 0.278 0.09 1 1008

Wood fiber TOP220

2.5 0.05 0.5 220 2100

Straw bale 25 0.067 3.73 120 1000

Ecoclay 4 0.24 0.17 1820 1000

Table 3.5 Layers’ characteristics and thermal properties. Internal partition. Straw-bale building.

Layers Thickness



Density (kg/m³)



1.8 0.13 0.14 650 1700

Straw bale 10 0.067 1.49 120 1000


1.8 0.13 0.14 650 1700

Table 3.6 Layers’ characteristics and thermal properties. Roof. Straw-bale building.

Layers Thickness



Density (kg/m³)


Sand and Gravel 10 2 0.05 1950 1045

EPDM 0.2 0.25 0.01 1150 1000


2.2 0.13 0.17 650 1700

Air Gap 10 0.469 0.21 1 1008


2.2 0.13 0.17 650 1700

Straw bale 25 0.067 3.73 120 1000


2.2 0.13 0.17 650 1700


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• Rammed earth building

Table 3.7 Layers’ characteristics and thermal properties. External wall. Rammed earth building.

Layers Thickness (cm) Conductivity (W/(m·K))


Density (kg/m³)


Rammed Earth 45 1.5 0.3 1855 2085

Table 3.8 Layers’ characteristics and thermal properties. Internal partition. Rammed earth building.



Density (kg/m³)


Rammed Earth 15 1.5 0.1 1855 2085

Table 3.9 Layers’ characteristics and thermal properties. Green roof. Rammed earth building.



Density (kg/m³)

Specific heat

(J/(kg·K))

Vegetable substrate

30 0.3 1 800 1000

Geotextile (PP) 0.3 0.22 0.01 910 1800

Drainage nodules (PS)

2 0.16 0.13 1050 1300

Geotextile (PP) 0.3 0.22 0.01 910 1800

EPDM 0.2 0.25 0.01 1150 1000

Pine Wood C24 2 0.13 0.15 420 1600

From Table 3.2 to Table 3.9 enclosures characteristics of both buildings are detailed. However, in addition,

in Table 3.10 a comparison in terms of heat transfer coefficient between both buildings is shown. Logically,

both buildings have the same U-Value for Slab-on-ground floor and Internal floor slab, as their definition

is identical. However, looking at the other envelopes, it can be seen that in terms of U-value, the straw-bale

building is significantly better, as would be expected due to the thermal characteristics of the materials

employed. Above all, there is an important difference in the external walls, which have a heat transfer

coefficient of 0.20 W/(m2·K) for the straw-bale building and 2.13 W/(m2 ·K) for the rammed earth building,

respectively. In addition, the U-value in the case of the roof is 3 times higher in the earth building than in

the straw-bale building. This will mean, as will be seen in the results (Section 4.1), a worse performance of

the earth building, at least in the building without energy improvements. Nevertheless, one of the objectives

of the current study is to assess the influence of thermal inertia, which is higher in the earthen house

envelope, which is a strength in its favour.


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Table 3.10 Heat transfer coefficient (U-Value) of the different enclosures. Comparison.

Enclosure External Wall Partition Wall Slab-on-ground

floor Internal floor

slab Roof

Heat Transfer coefficient

[U] (W/(m²·K))

Straw-bale building

0.20 0.49 0.38 0.55 0.22

Rammed earth building

2.13 2.78 0.38 0.55 0.68

3.5.3.2 Activity

In this section, the characteristics relating to the activity of the building shall be indicated, including

occupancy, use of equipment, artificial lighting, and ventilation. All this, in order to select an official and

international reference, has been established by the European standard EN 16798-1:2019 [159].

• Occupation:

In accordance with the aforementioned standard, the following values have been introduced for building

occupancy (Table 3.11), differentiating between the private spaces (living area) and the common area

(corridor), in terms of schedule (from Figure 3.5 to Figure 3.8):

Table 3.11 Occupation inputs for the initial model of the building.

Parameter (Unit) Value

People (m2/person) 28.3

Activity level (W/person) 118.86

Sensible fraction 0.67

Radiant fraction 0.6

- Private:

Figure 3.5 Occupation schedule for weekdays in private spaces.


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Figure 3.6 Occupation schedule for weekends in private spaces.

- Common Zone:

Figure 3.7 Occupation schedule for weekdays in common zones.

Figure 3.8 Occupation schedule for weekends in the common zone.


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• Equipment:

As indicated in EN 16798-1:2019, the power and the usage schedule of the appliances are indicated below

(Figure 3.9 and Table 3.12). It has been assumed that no appliances are used in the common zone, only in

private dwellings. This equipment corresponds to television, fridge, washing machine, oven, and others. The

type of energy vector used in the appliances is electricity.

Table 3.12 Equipment inputs for the initial model of the building.


Design power (W/m2) 3


Latent fraction 0

Figure 3.9 Equipment schedule in private spaces.

• Lightning:

In the same line, lightning has been defined, but in this case, it has been determined in the same way for the

private and the common zones, without distinction. The values and schedule for lightning are presented in

Table 3.13 and Figure 3.10, respectively:

Table 3.13. Lightning inputs for the initial model of the building.


Installed light power (W/m2) 15


Space fraction 1


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Figure 3.10 Lightning schedule in private and common zones.

• Ventilation:

As regards the ventilation of the building, since this is a fundamental aspect in terms of the health of the

tenants, not only the value indicated by the selected standard must be determined, but also compliance with

the corresponding regulations in each of the countries where it is applied must be checked. In the initial

model, the building is ventilated naturally and, according to EN 16798-1:2019, the constant air flow is

established in 0.8 l/(s·m2) for the whole year. This is defined in Cypetherm EPlus as natural ventilation for

the initial models.

According to the Public Health Agency of Sweden FoHMFS 2014:18 [179], the minimum outdoor airflow

must be 0.35 l/(s·m2). However, considering that the minimum ventilation rate should not be less than 4

l/(s·person) and assuming that the building has a maximum of about 40 people, the ventilation flow

obtained is around 0.15 l/(s·m2), which is less than the minimum required. Therefore, the minimum required

(0.35 l/(s·m2)) is more restrictive, but still lower than the model value of 0.8 l/(s·m2), thus proving

compliance with the Swedish standard. No mechanical ventilation or heat recovery system is employed in

the initial model.

On the other hand, according to the DB HS [180] of the Spanish Technical Building Code [156], the

minimum ventilation flow for residential buildings depends on the zones, as indicated in Table 3.14.

Table 3.14 Minimum flow rates for constant flow ventilation in habitable rooms. DB HS [180].

Minimum ventilation flow (l/s)

Dwelling size Dry zones Wet zones

Double Bedroom

Remaining Bedrooms

Living/dining rooms

Minimum in total

Minimum by zone

0-1 Bedrooms 8 - 6 12 6

2 Bedrooms 8 4 8 24 7

3 or more Bedrooms 8 4 10 33 8


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Table 3.15 Ventilation flow calculation for one dwelling.

Ventilation flow (l/s)

Dry zones

Living-Dining 10

Lobby -

Double Room 8

Single Room 4

Total 22

Wet zones

Bathroom 7

Dining-Kitchen 7

Total 14

Total ventilation 24

In Table 3.15, the ventilation flow for one single dwelling is calculated according to DB HS. Since the

addition of the different zones is lower than the minimum in total (24 l/s), this is the one applied for the

dwelling ventilation, as specified in the normative. Considering that each dwelling has a floor area of 63.06

m2, the ventilation flow required in Spain is 0.38 l/(s·m2). Therefore, it has been verified that using 0.8

l/(s·m2) in the model is sufficient to comply with Spanish and Swedish health regulations.

• Thermal bridges, Infiltrations, Condensation, and Set-point temperatures:

Thermal bridges have been defined according to CTE DB-HE [157], in function of the typology of the

joint. In this case, it has been considered that there is continuity in the thermal insulation at all junctions.

Values of thermal lineal transmittance of the thermal bridges can be checked in Annex I.

Moreover, as far as infiltrations are concerned, the air permeability of the building envelope must be defined

per square meter of the enclosure, having selected the default values shown in Table 3.16. This air leakage

rate is set for a reference pressure difference of 100 Pa.

Table 3.16. Air permeability of the building for a reference pressure of 100 Pa.

Enclosure Air leakage (m3/h·m2)

External Wall 16

Roof 16

Doors 60

Openings 10

The analysis method employed for infiltrations calculation is based on the enhanced model (ASHRAE

[181]), with the data shown in Table 3.17.

Table 3.17 Analysis data in the enhanced model for infiltrations calculation

Coeff. Value

Stack coefficient 0.078

Pressure exponent 0.67

Wind coefficient 0.142

Shelter factor 0.5

Finally, since it is very important to avoid dampness in the cladding for structural reasons, it has been

decided to test the occurrence of dampness in strawbale construction. For this purpose, the simulation


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checks, in accordance with ISO 13788 [182], the existence of surface or superstitial condensation, which is

calculated by the simulation software.

Set-point temperatures have been established in 20ºC for heating and 26ºC for cooling as indicated in EN

16798-1:2019.

3.6 Energy simulation

Once the model is finished in Cypetherm EPlus, energy simulation must be done. But first, it is necessary

to define the location data (coordinates, weather, orientation…). As said before, Cypetherm EPlus is an

interface whose calculation engine is EnergyPlus. The results are shown directly in Cypetherm EPlus, but

for more detailed information, the file created can be simulated in EnergyPlus itself.

Simulations are divided in function of the material used as insulation, straw, or earth, and subdivided into

the different climates. First, weather analysis is done in order to evaluate the climate conditions in which

the buildings are located in the model. The simulations are performed in the following order, which

corresponds to each scenario:

- Straw-bale building in Stockholm.

- Straw-bale building in Valencia.

- Earth building in Stockholm.

- Earth building in Valencia.

Before the execution of the different simulations, a climate analysis of the two locations was carried out.

The aim is to estimate the results to be obtained after the simulation so that they make sense. In addition,

the climate analysis allows for better energy optimisation of the buildings (Section 4.2) according to the

climatic conditions.

3.6.1 Climate Analysis

In the current section climatic parameters will be analysed, related to temperature, radiation, solar position,

and thermal comfort. For this purpose, use has been made of the Climate Consultant tool [183], which

allows the import of climate files in EPW format (which is the one used directly in Cypetherm EPlus) and

displays statistically-based information on all the data contained in the file.

3.6.1.1 Stockholm

Figure 3.11Monthly temperature range in Stockholm (ºC).


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Stockholm, being a Nordic city, winters are long, freezing, cloudy, dry, and snowy. On the other hand,

summers have comfort temperatures and are partly cloudy, in general. Different graphs, plotted in Climate

Consultant from the IWEC files, have been generated and analysed in this section.

As for temperatures (Figure 3.11), they are generally low throughout the year, going below -10ºC in the

winter months (November - March) in the average low temperatures. Likewise, in these months, the

maximum temperature hardly exceeds 5ºC. These temperatures are far from the comfort temperatures

(20ºC-26ºC) established in the building, which translates into great efforts of the installed heating systems

to cover the demand in the case that passive strategies are not adopted to reduce the demand and therefore

the consumption of the equipment. The warmer months, however, always have temperatures above 0°C,

but the average temperature is still slightly below the indoor set-point temperature. Furthermore, the

temperature does not exceed 26°C at almost any point all around the year, therefore, with good building

design, there would be no need for high consumption of cooling systems.

Figure 3.12 Monthly radiation range in Stockholm (W/m2).

Figure 3.13 Monthly sky cover range in Stockholm (%).


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In reference to solar radiation (Figure 3.12), Stockholm, being a high latitude city (59.65º) has a low solar

height compared to other locations closer to the equator. This, together with the high percentage of clouds,

results in low solar radiation, and especially low direct normal irradiation (DNI). If the DNI is observed

with respect to the global horizontal irradiation (GHI), in most months the latter is higher than the direct

solar radiation, even considering that the DNI is measured perpendicular to the sun's rays. This is mainly

due to the fact that diffuse radiation is high in proportion. In any case, given the short daylight hours in the

winter months and the solar height throughout the year, the theoretical solar radiation is also not high. As

shown in Figure 3.12, in the winter months (October - March) the GHI rarely exceeds 300 W/m2, with an

average of around 100 W/m2 and in the summer months, the maximum is 600 W/m2, the average being

around 300 W/m2. This, on the one hand, has the favourable aspect that in summer, the cooling efforts

will be less than in other locations with higher solar radiation, and on the other hand, in the winter months,

it will not be possible to make much use of this radiation for the natural heating of the building.

Regarding the sky cover or cloud coverage (Figure 3.13), the average is substantially high, between 50% and

75% all around the year, which affects the solar radiation as was pointed previously.

Figure 3.14 Hourly sun position chart in Stockholm (º).

In the same line, concerning the sun position, in Figure 3.14, the hourly sun position chart from December

21 to June 21 (Winter-Spring) is shown, which has the same shape as the analogue chart from June 21 to

December 21. It can be observed that the altitude angle is low (in comparison to other southern locations).

In addition, the bearing angle range is narrow in winter months (-40º - 40º) and wide in summer months (-

130º - 130º). Due to the low temperatures in Stockholm and the position of the sun, placing windows in the

south could be interesting from an energy point of view in order to increase the solar gains through them.

However, the optimization criteria considered in the current project do not allow to change the geometry

of the building as a passive strategy (not even the windows), so windows are to be left as they are in the

original building.

In Figure 3.15, a psychrometric chart is shown, where a point cloud is plotted, representing the 8760 hours

of the year in function of the temperature and humidity in each moment. In addition, a comfort area is

represented, according to ASHRAE [184] (this is not the comfort area considered in the project, but similar).

This gives an idea of how difficult is to provide indoor comfort conditions. As it could be seen in Figure

3.15, the main part of the point cloud is located on the left side with respect to the comfort zone, which

corresponds to cold temperatures. The major number of points are located around 0ºC, finding points

below and over that temperature, but still so far from comfort conditions. This fact means that, if not an

adequate building design is adopted, the heating demand will be large. Additionally, if just the points inside


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the thermal zone are considered, only 4.7% of the time, outdoor conditions are satisfactory from a comfort

point of view. In Stockholm, taking as a reference the psychrometric diagram, only heating measures must

be applied, as almost any point is placed in the right part of the chart.

Figure 3.15 Psychrometric chart with comfort zone according to ASHRAE in Stockholm.

3.6.1.2 Valencia

In Valencia, in contrast to Stockholm, as a Mediterranean city, summers are hot, humid, and clear, and

winters are moderate, partly cloudy, and windy. From an energy perspective, Valencia is a favourable place

for buildings, as weather conditions are relatively adequate. Some graphs have been analysed in this section

as well for Valencia.

Figure 3.16 Monthly temperature range in Valencia (ºC).

Concerning dry temperatures in Valencia (Figure 3.16), values are moderate throughout the year. In winter,

temperatures rarely reach 0ºC, and the average temperature is above 10ºC with maximum temperatures of

around 20ºC, which are already comfort conditions, which means that the heating demand is not as high as

in other climates such as that of Stockholm. As for the summer months, the average temperature is within


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the comfort range, but the maximum temperatures are above 30ºC, which will require the use of cooling

systems to ensure an adequate temperature inside the house. This makes Valencia an adequate city for

sustainable building, as designing a highly efficient building (in terms of energy performance) is relatively

reasonable and affordable.

Figure 3.17 Monthly radiation range in Valencia (W/m2).

Solar irradiation in Valencia (Figure 3.17), due to the clear sky and the latitude (39.5º), is high in comparison

to other northern locations, such as Stockholm. It must be taken into account that the DNI is measured in

a perpendicular way to the sun position and the GHI is measured horizontally to the ground, for that reason,

in winter months, when the solar altitude angle is low, the DNI is higher than the GHI. The mean value of

irradiation (DNI and GHI) in cold months is between 200 W/m2 and 350 W/m2, going beyond 500 W/m2

in DNI. In addition, in the summer months, the average DNI and GHI are between 350W/m2 and 500

W/m2, reaching maximum values over 800 W/m2 in GHI. On the one hand, having high irradiation values

in the winter months, when temperatures are below 20ºC, is a feasible way to warm up the building by

means of solar gains through the windows, taking advantage of the greenhouse effect. On the other hand,

in summer, irradiation becomes a problem since the outdoor temperature is usually high, and sun rays hit

the building enclosures and, especially, pass through glazed openings increasing the indoor temperature.

Passive measures must avoid sun rays hitting windows by means of shadowing strategies.


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Figure 3.18 Monthly sky cover range in Valencia (%).

In relation to irradiation, sky cover by clouds gives a reference to how much direct irradiation will interfere

with the building performance. In Figure 3.18, it could be observed that the mean sky cover percentage is

between 30% and 50%, finding the lower values in summer months (June, July, and August).

Figure 3.19 Hourly sun position chart in Valencia (º).

In Figure 3.19, the hourly sun position “bell” chart is represented, and it could be seen that the sun altitude

angle in the summer months is close to the zenith angle. At noon, the sun altitude is around 75º (21st of

June). Additionally, concerning the bearing angle, in summer the sunrise occurs at -120º and the sunset at

120ºC. This has to be considered when designing the building, because, in the evening and the morning,

sun rays hit East and West façades (due to its altitude and bearing angles). For that reason, solar gains

through windows placed in those façades must be avoided in the summer months by shadowing or just not

placing much glazed surface there.


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In winter (21st of December), the altitude of the sun is much lower (~25º), but ever higher than in other

northern countries such as Sweden. In this chart, the period Winter - Spring is represented, but it is the

same chart as the Summer-Fall one. As mentioned before, solar irradiation can be used in winter to warm

up the building and, considering the sun position in these months, placing windows in the South façade is

an adequate solution to have solar gains through them. At the same time, in summer, the sun altitude in the

central hours of the day is high, so the solar rays are almost horizontal to that façade and they are easily

shadowed by awnings.

Figure 3.20 Psychrometric chart with comfort zone according to ASHRAE in Valencia.

As said before, in Figure 3.20, a psychrometric chart is shown, where a point cloud is plotted supplemented

by a comfort area according to ASHRAE [184], representing the 8760 hours of the year in function of the

temperature and humidity in each moment. In this case, the point cloud, in comparison to the chart for

Stockholm (Figure 3.15) in placed more to the right, which corresponds to a warmer climate. For that

reason, a greater number of points can be found inside the blue area (comfort area), resulting in 16.7% of

the total number of points. Therefore, that percentage means that in 1461 hours of a typical year, the

comfort conditions occur outdoors. If it is compared to Stockholm, in which only 412 hours were comfort

hours, it is possible to conclude that Valencia is a more suitable place to build a sustainable building as it is

easier to reduce the demand due to the climate conditions. Notwithstanding, a different design should be

developed in each of the climates to reduce the demand as much as possible from a technical and economical

approach. In Valencia, as a conclusion of the psychrometric chart, cooling and heating measures must be

applied.


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4 Results and Discussion

4.1 Energy simulation

Once the different energy simulations are carried out in Cypetherm EPlus, results for each scenario are

obtained. These simulations have been conducted as described in Chapter 3 according to the model created

for each material and climate. The results of the simulations as a function of the material used and the

building location are shown below.

4.1.1 Straw-bale building

4.1.1.1 Stockholm

As it could be seen in Figure 4.1, where demand in terms of energy and capacity is represented, heating

demand is large all around the year, in comparison to cooling demand. Especially in the winter months,

where outside temperatures are below 0°C, as can be seen in Section 3.6.1, the heating demand is far from

that of a highly efficient building. Moreover, the heating demand is not reduced in summer as the

temperature is below comfort conditions for a significant part of the time. Regarding the cooling demand,

it could be observed in Figure 4.1 that, in the summer months, some capacity is required at certain times,

but it is insignificant compared to the heating demand. These small peaks occur when the temperature inside

the building, as a consequence of the outside climatic conditions, is above the setpoint temperature of 26ºC.

Figure 4.1 Annual energy and capacity of the straw-bale building in Stockholm.

In annual terms, the following results for demand per unit of air-conditioned building area are obtained:

Heating demand = 140.00 kWh/(m2·year)

Cooling demand = 0.22 kWh/(m2·year)

Taking Passive House certification as a reference, the heating demand is almost 10 times higher than the

value established of 15 kWh/(m2·year) established by PHI. As a result, it will be necessary to incorporate

passive strategies in the building to reduce the heating demand, as indicated in Section 4.2. No action will

be needed on the cooling demand, as it is already at a minuscule value, not because of the design of the

building but because of the climate in which the building is located. Despite this, the optimisation will be

carried out to meet both heating and cooling demand, without neglecting the latter.


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Figure 4.2 Temperature evolution outdoor and in air-conditioned areas. Straw-bale building in Stockholm.

With reference to comfort, Figure 4.2 shows the evolution of the indoor temperature throughout the year

in the private residential areas (air-conditioned), and the evolution of the outdoor temperature is also shown.

The average outdoor temperature is practically always below the comfort temperature, which explains the

high heating demand. As for the indoor temperature, it is always in the range 20ºC and 26ºC, since these are

the setpoint temperatures that have been established and the air-conditioning systems have been defined as

Infinite Power Systems (IPS), which, as their name indicates, can cover the entire demand, however great it

may be.

Figure 4.3 Temperature evolution outdoor and in not air-conditioned areas. Straw-bale building in Stockholm.

Figure 4.3, on the contrary, shows the evolution of the temperature in the common areas (corridor, hallway,

etc.), which are not air-conditioned and therefore have not been assigned setpoint temperatures for heating

and cooling. In addition, this graph also shows the average daily outdoor temperature for comparison. The

temperature in the common areas is always higher than the outside temperature, which is due to heat transfer

through the interior partitions from the private areas, which are air-conditioned, and due to solar gains

through the windows and internal thermal loads (occupancy, equipment, kitchen, lighting...). In Figure 4.3

it can be seen that in the winter months 0ºC is reached at some point in the common areas and in the

summer, it reaches a maximum of 30ºC. In summer, this is not a problem, since it is a non-air-conditioned

area, it is consistent to have a temperature of 30ºC, which is only 4ºC above the comfort temperature (26ºC).

However, in winter, temperatures close to 0ºC are considered to be far from the comfort temperature

(20ºC), which is unacceptable even for a non-air-conditioned area. Therefore, the aim is not only to optimise

the dwelling in terms of energy but also to the comfort of the tenants.

Prior to the optimisation of the building, the weak points to be improved in the building have to be identified

by analysing the energy balance of the building, which reveals the most important heat flows that cause the

building to have such a high heating consumption throughout the year. This energy balance is represented

by means of a bar diagram in Figure 4.4.


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Figure 4.4 Annual energy balance of the straw-bale building in Stockholm.

The energy balance again illustrates the high heating demand (Qh) of the building and the low cooling

demand (Qc) of the building. These system demands compensate the other heat flows of the building until

zero balance is achieved. Regarding the sign criteria, positive values refer to the heat flow incoming to the

building and negative values to the heat flow outgoing from the building. Thus, it can be seen in Figure 4.4

that the most negatively influencing aspect is the heat lost through ventilation and infiltration of the building

(Qve+inf), which stands out above the rest. This must be considered in energy optimisation, without

neglecting the health criterion that requires a certain ventilation rate.

On another hand, the heat flow through the opaque cladding (Qop) is also of some importance, however,

the thermal transmittance coefficient of the cladding is already quite low. In addition, the straw and timber

modules used in the building have a specific thickness and, as indicated in section 4.2, no modification in

terms of building geometry is envisaged. In addition, the heat flow through the windows (Qw) has a high

influence in relation to the glazed surface. Windows in the initial building have a thermal transmittance

coefficient of 2.9 W/(m2·K), so they can be easily improved. There is a positive influence of the windows,

which is higher in the summer months that correspond to the solar gains through them. Notwithstanding,

as it is positive, no action must be taken to avoid this.

Concerning the internal thermal loads, they have a low but positive influence as they provide heat to the

building, which helps the heating system to compensate for the heat losses. These thermal loads correspond

to the occupation (Qocup), lightning (Qlight), and equipment (Qequip). They cannot be modified as they are

fixed, and no action can be taken to amplify their influence.

No vapour condensation occurs in any of the enclosures, avoiding degradation problems, as can be checked

in Annex II, as this one is the most critical scenario.

4.1.1.2 Valencia

In Figure 4.5, where the annual demanded for energy and power of the straw-bale building in Valencia are

represented, it could be seen that cooling and heating are balanced. Valencia, being a Mediterranean city,


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winters are moderate, and summers are hot and humid, as explained in Section 3.6.1.2. Therefore, this

equilibrium is logical as in summer temperature is higher and a cooling system is needed to meet the demand.

Obviously, in winter, due to the fact that the temperature is lower than 20ºC, a heating system is also needed.

However, considering the large building surface, the values observed in Figure 4.5 are low. This is thanks,

partly, to the good insulation properties of straw.

Figure 4.5 Annual energy and capacity of the straw-bale building in Valencia.

In annual terms, the following results for demand per unit of air-conditioned building area are obtained for

the straw-bale building located in Valencia:



The normalised values per unit area and year are closed to those defined by Passive House certification.

PHI defines a maximum demand for heating and cooling of 15 kWh/(m2·year). Being so close to that value,

few passive strategies are going to be needed to have a highly efficient building. This is due to the initial

insulating level the building initially has, thanks to straw-bales thermal properties.

In Section 4.2 optimization measures are explained, and then, in Section 4.3, those strategies are analysed.

Figure 4.6 Temperature evolution outdoor and in air-conditioned areas. Straw-bale building in Valencia.

Apart from the energy performance results, comfort conditions (20ºC-26ºC) are also analysed as it is

considered an important factor to consider. In this project, the comfort conditions have been defined as the

parameters to assess thermal comfort. In Figure 4.6 the temperature evolution in air-conditioned areas, as

well as the outdoor temperature, are represented. Logically, the indoor temperature in private dwellings is

all time between 20ºC and 26ºC, thanks to HVAC systems. The light blue line represents the mean daily


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outdoor temperature, which is very close to comfort conditions all around the year, especially, from May to

October.

Figure 4.7 Temperature evolution outdoor and in not air-conditioned areas. Straw-bale building in Valencia.

Concerning the indoor temperature in common areas (not air-conditioned) is also represented together with

the outdoor temperature in Figure 4.7. As there is no air-conditioning system, the temperature in the

common areas is often not comfortable. However, temperatures are rarely below 15ºC or above 30ºC, only

5ºC below and above the setpoint comfort temperatures (20ºC and 26ºC). This is therefore considered an

acceptable range and does not pose a problem in terms of tenant comfort. However, with the energy

upgrading of the building, these conditions will be further improved. Indoor temperature is always over the

outdoor temperature, due to solar radiation through the windows, heat flow coming from private areas,

internal thermal loads (occupation and lightning).

In order to see the building's weak points in this climate that could be improved, the energy balance of the

building, which is represented by means of a bar chart in Figure 4.8, is analysed.

Figure 4.8 Annual energy balance of the straw-bale building in Valencia.


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In Figure 4.8, the building energy balance is displayed, where negative values represent the heat flow towards

the outside of the building and the positive values towards the inside of the building. That way, it could be

seen the energy demanded by the heating (QH) and cooling (QC) systems, which are ideal. These energy

flows are intended to compensate for the rest of the heat flows. Due to the high ventilation rate (0.8 l/s/m2),

in winter months, it is the main weak point, at is suppose the major energy loss which must be covered

partially by the heating system. Nevertheless, in summer, when cooling is needed in the building, ventilation

can become advantageous when the outdoor temperature is lower than the indoor temperature, but it could

be also negative when ventilation occurs in the opposite situation.

Apart from that, heat exchanges occur through opaque enclosures (Qop) and glazed openings (Qw) in both

directions depending on the conditions of temperature or solar radiation in each case. These heat flows are

low in absolute value taking into account the excellent energy performance of the building. However, in

relation to the rest of the parameters, they are not negligible. As mentioned previously, the energy

performance optimization is carried out without modifying the geometry of the building, so the thickness

of straw modules (insulation) is not increased. However, in relation to windows, they could be improved in

order to reduce the heat transfer through them by conduction. In addition, as it could be seen in Figure 4.8,

in summer months, thermal gains through windows have a certain importance, due mainly to solar

irradiation, which, if necessary, could be avoided by placing shadowing elements or redistributing the

windows on the building façade.

As for the internal loads of occupancy (Qocup), lighting (Qlight), and equipment (Qequip), they are a relatively

important factor in the energy balance of the building as can be seen in Figure 4.8. However, as these have

been defined according to the regulations, no action can be taken on them in any case. These internal loads

provide heat to the interior of the building, which is beneficial in the winter months, thus reducing the

heating demand, but detrimental in the summer, which forces the cooling systems to have a higher

consumption to cover the demand.

4.1.2 Rammed earth building

4.1.2.1 Stockholm

In Figure 4.9, an annual evolution of the total energy demand, and capacity needed to cover is represented.

As it could be seen, no cooling capacity (blue line) is needed due to climate conditions and building

characteristics. However, a large amount of heating energy (red line) is demanded all around the year. This

is mainly because the climatic conditions are extreme in terms of temperature, solar radiation, and other

factors, as explained in Section 3.6.1. In addition, the rammed earth building, since no insulation material

has been included, has a high thermal transmittance, as indicated in Section 3.3, which makes the heat

transmission towards the outside of the building high, given the temperature difference. In the summer

months, as observed in Figure 4.9, heating demand is low, as the temperature is close to comfort conditions,

but in winter, when the temperature is below 0ºC, HVAC systems had to make big efforts to meet the

energy demanded.


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Figure 4.9 Annual energy and capacity of the rammed earth building in Stockholm.


the rammed earth building located in Stockholm:



The normalized heating and cooling demand, per year and squared meter, give clear information about the

energy performance of the building. In this case, as foreseen, heating demand is extremely high in

comparison to Passive House criteria, where maximum heating demand is 15 kWh/(m2·year) (Section 3.1).

Figure 4.10 Temperature evolution outdoor and in air-conditioned areas. Rammed earth building in Stockholm.

In Figure 4.10, the indoor temperature evolution of the conditioned areas is represented together with the

outdoor temperature. As can be seen, the indoor temperature is always around 20ºC, which is the setpoint

temperature established in the heating systems, but in winter months temperature is below that value due

to the margin of operation of the systems. When the indoor temperature is above 20ºC, the heating systems

are switched off, as the outdoor conditions, together with the internal loads, are sufficient to achieve an

energy balance. However, this is only at specific and limited times of the year, as heating is required most of

the time.


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Figure 4.11 Temperature evolution outdoor and in not air-conditioned areas. Rammed earth building in Stockholm.

In Figure 4.11, the temperature of not air-conditioned zones (common zones) is represented, as well as the

outdoor temperature. For the rammed earth building located in Stockholm, as can be seen in the graph, the

temperature is in some points below 10ºC in common zones during winter, but the rest of the year, the

temperature is close to comfort conditions. This is due to the fact that internal partitions in this building

design do not have insulation either (Section 3.3). For that reason, since private areas are air-conditioned

(~20ºC), common areas are warmed up by means of heat transfer through these partitions. This supposes,

on the one hand, higher demand for the heating system, but, on the other hand, more favourable conditions

in common areas, from a comfort perspective, in comparison to the straw-bale house (Section 4.1.1).

Figure 4.12 Annual energy balance of the rammed earth building in Stockholm.

In Figure 4.12 the annual energy balance of the rammed earth building located in Stockholm city is

represented, where different heat flows are plotted through a bar chart. The heating demand analysed above

is intended to offset the other heat flows to achieve the net balance in the building. Since there is only this

demand, and there is no cooling demand, the only heat flows that are detrimental are those with a negative


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value, which are those that flow from the inside to the outside of the dwellings. The most negatively

influencing factor is the heat flow through opaque enclosures (Qop) (external walls, roof, and floor in contact

with the ground). In the rammed earth building, due to the lack of insulation, the thermal transmittance of

the thermal envelope is high, therefore, in a location as cold as Stockholm, heat transmission is significant.

Thermal inertia in such climates does not affect since the average temperature is not close to comfort

conditions. For this reason, the damping of the heat wave, and its consequent phase shift, do not provide

any benefit from an energy point of view in cold climates.

As in the straw-bale building at the same location, ventilation, and uncontrolled air infiltration (Qve+inf) have

a great influence on the thermal aspect. These factors negatively affect the heat balance of the building, due

to the low temperatures of the outside air, which enters the building untreated. The HVAC system takes

care of raising the air temperature to a comfortable thermal level. Improvement measures should be

implemented to reduce this influence, as indicated in Section 4.2.1.

The other aspect, which does not stand out as much as the previous ones in Figure 4.12, but which is also

important, is the heat transmission through the windows (Qw), which are originally double-glazed with an

air chamber, but with a U-value of 2.9 W/(m2·K) and carpentry with a U-value of 3.2 W/(m2·K). They

could be improved to reduce heat transfer.

Thermal internal gains, which are occupation (Qocup), lightning (Qlight), and equipment (Qequip), in relative

terms, are not important, and they hardly contribute to heating purposes.

One positive aspect that could be exploited is the solar gain through the windows (Qw), which has a positive

value on the heat balance of the building. However, in order to take advantage of this, the geometry of the

building would have to be modified by increasing the glazed area, mainly on the south façade.

4.1.2.2 Valencia

As in previous sections, the energy demanded by the building in terms of heating and cooling is represented

in an annual bar chart (Figure 4.13), as well as the capacity in Watts for each moment of the year. As

expected, due to the outdoor temperature evolution throughout the year and the climate conditions in

Valencia, the energy performance of the building is better than in Stockholm. Heating demand is

substantially higher than cooling demand. This is because, in summer, the average temperature is close to

the comfort temperature established, therefore, since the external walls have thermal inertia, although not

insulation, the heat wave is damped, and energy demand values are not very high. On the other hand, in

winter, the average daily temperature is far from the setpoint temperature of the HVAC equipment, so

thermal inertia is not a real benefit in terms of heating demand. Also, as the external envelopes lack an

insulation layer, the heat flow easily enters the building, placing a high demand on the heating system.

Figure 4.13 Annual energy and capacity of the rammed earth building in Valencia.


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the rammed earth building located in Valencia:



In terms of cooling demand, the building performs close to the Passive House criterion of 15 kWh/(m2·K)

Despite the lack of insulation in the envelope, a cooling demand very similar to that obtained in the building

constructed with straw bales is achieved, whose thermal transfer coefficient of the walls is 10 times lower.

This is due to the fact that outdoor temperature in summer is closer to set-point temperatures than in winter

and no insulation is required.

As for the heating demand, the weak point of this building can be observed once again, which is the lack of

insulation in the external enclosures. The energy demand, in this case, is over 60 kWh/m2/year, which is

three times higher than in the thatched house for the same climatic conditions.

Figure 4.14 Temperature evolution outdoor and in air-conditioned areas. Rammed earth building in Valencia.

In Figure 4.14, outdoor and indoor temperature (for air-conditioned areas) is represented for the rammed

earth building in Valencia. Thanks to the IPSs, the indoor temperature is always between the setpoint

temperatures (20ºC-26ºC). However, to achieve these conditions, energy consumption is required by the

heating and cooling systems.

Figure 4.15 Temperature evolution outdoor and in not air-conditioned areas. Rammed earth building in Valencia

In Figure 4.15, the outdoor and not air-conditioned zones temperature evolution is represented. Since those

areas are not air-conditioned, comfort temperatures are not achieved all time. Nevertheless, the minimum

temperature reached is 15ºC in winter months and the maximum temperature is 30ºC, which are acceptable

values for common areas since tenants are not spending much time there. This temperature is a consequence

of the outdoor temperature, and of the heat transfer from the private zones, which are in comfort conditions

thanks to HVAC systems.


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Figure 4.16 Annual energy balance of the rammed earth building in Stockholm.

As is done for each scenario, an analysis of the annual energy balance of the building is carried out to identify

the influencing factors and weaknesses to be improved. Firstly, once again, the heating and cooling demand

that compensates for the other heat flows are shown, which are analysed above in the current section.

The most important negative factor is the heat flow through opaque enclosures. This is mainly due to the

lack of insulation in the external walls. In winter, this is a major problem as the heating demand is high, but

in summer, thanks to the temperature evolution and the thermal inertia of the compacted earth, the heat

flow through the walls is balanced and negligible.

Secondly, mainly ventilation, but also infiltration, is an influential factor from the point of view of heat loss

from the building, contributing negatively to a worsening of the thermal performance of the building in the

winter months, when heating is required. However, it also has a positive side, and that is that in summer,

this ventilation can be used to further reduce the energy consumption of the cooling systems.

As for the windows, they could be slightly improved to reduce the heat flow through them, as they represent

a large part of the façade surface in the building and have a poor thermal transmittance. The heat flow

through the windows is partially eclipsed by the heat flow through the walls, but this does not mean that it

should be disregarded. Another heat flow that brings heat into the building is solar radiation through glazed

openings, which can be used in winter but should be avoided in summer.

Finally, concerning the internal thermal loads, which are occupancy, lighting, and equipment, they bring

heat into the building.


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4.2 Energy performance optimization – Measures

Once the initial building simulations are carried out in the different climates, results are obtained and

analysed. Based on those analyses, which can be found in the present thesis document in Section 4.1, an

energy performance optimization is carried out for each scenario in this section. Optimization can be

performed including different passive measures, but it is not allowed to change the geometry of the building

or the glazed surface distribution. Changes in insulation thickness, ventilation, materials, infiltrations,

shadowing, and others can be done to reduce energy demand.

4.2.1 Straw-bale Building

4.2.1.1 Stockholm

Based on the results obtained (Section 4.1.1), and taking into account the climate conditions in Stockholm

(Section 3.6.1.1) and the improvement opportunities detected, the straw-bale building model has been

modified including the following measures, which reduce the energy performance and comfort:

• Heat Recovery Ventilation (HRV) (Eff. 85%)

As can be seen from the results (Section 4.1.1), the most influential factor in the high heating demand is

ventilation, together with air infiltration. This is mainly due to the fact that the outdoor temperature is

extremely low and, this air enters the building during natural ventilation. At the same time, already heated

air is expelled from the building. Therefore, the heating system must at all times raise the outside air

temperature to comfort conditions, which requires a great amount of energy. For this reason, since

ventilation cannot be avoided for health reasons, an HRV and a mechanical ventilation system have been

adopted as a measure to increase the fresh air temperature at the building inlet. The nominal efficiency of

HRV is usually between 50% and 90% [185]. Thus, given the requirements, a highly efficient enthalpic HRV

has been selected, with an efficiency of 85% both for sensible and latent heat. The enthalpy HRV allows

not only heat exchange but also humidity exchange, achieving optimal comfort conditions inside the

building.

Figure 4.17 Enthalpy heat recovery ventilator working principle [186].

HRV working principle can be observed in Figure 4.17. In summer, cooling and dehumidification of the

outdoor air are carried out and, in winter, heating and humidification are carried out.

These HRV characteristics have been defined in Cypetherm EPlus, assigned to private and common zones,

substituting natural ventilation (established in the initial model). The system is always working as it cannot

be defined in another way in Cypetherm EPlus, which can suppose a worse energy performance in summer

where natural ventilation could cool down the building in certain moments.


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• Air permeability improvement

As explained in Section 4.1.1, infiltration, as well as the ventilation airflow, has a negative effect on the

heating demand, as very low-temperature air from outside is brought into the building. This air is heated by

the heating systems to comfort conditions that consume large amounts of energy.

Infiltrations are not-controlled and not-desired air leakages through enclosures, doors, windows. For that

reason, it is not possible to install an HRV as in mechanic ventilation. In this case, the only solution is to

reduce them by means of a better design or better construction practices.

Therefore, according to the Passive House criterion about air leakages, infiltrations have been reduced in

Cypetherm EPlus until 0.6 renovations/hour for a pressure difference of 50 Pa are reached. This has been

done by an iterative process. The resulting infiltrations are the following (Table 4.1), where the air

infiltrations are defined for a reference pressure difference of 100 Pa, which is the one used in the software:

Table 4.1 Improved Air permeability of the building for a reference pressure of 100 Pa.

Enclosure Air leakage (m3/h·m2)

External Wall 4

Roof 4

Doors 15

Openings 7.5

• Triple glazed windows – Argon gas

Windows have been identified in Section 4.1.1 as a weak point to improve. Initially, as indicated in Section

3.3, windows were defined as old double-glazed with an air gap between glass, which corresponded to a

heat transfer coefficient of 2.9 W/(m2·K). These windows are going to be replaced by others with triple

glazing and a double argon gas chamber, reducing the heat transfer coefficient to 0.9 W/(m2·K) [164].

The window frames have also been upgraded, so that the new model is fitted with wooden frames with a

U-value of 2 W/(m2·K), according to an article that deals with a heat transfer analysis of timber windows

[187]. Windows are supposed to be coupled with these frames and placed in the building envelope carrying

out good construction practices, having a low air leakage rate (7.5 m3/h·m2) as indicated before in this

section.

• Insulation improvement study – not applied

Opaque enclosures also play an important role in the thermal balance of the building, as observed in Section

4.1.1. However, as no modification of the straw-bale thickness is allowed in this project, it has been decided

to carry out a parametric study to see the influence of insulation thickness in the different enclosures. Roof

and external walls use the same insulation material (straw-bales) so they are studied together. The floor uses

a different material, and it is in contact with the ground, so it is treated separately.

In addition, the heat transfer coefficient of external walls and roof, which have straw as insulation material,

is 0.2 W/(m2·K) and 0.22 W/(m2·K), while the U-Value of the slab-on-ground floor is 0.38 W/(m2·K), as

indicated in Section 3.5.3.

In any case, a parametric study has been carried out to check the effectiveness of this measure. However,

Cypetherm EPlus does not have any parametric tool.

The parametric study has been done through the Parametric Preprocessor of EnergyPlus. First, EnergyPlus

must be able to read the exported file from Cypetherm EPlus, and then different parametric objects must

be used to perform the study.


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The main parametric object is Parametric:SetValueForRun which sets the value of the parameters to

different values depending on the run being simulated. The name of the IDF files that are created for each

run and the output files for each run is based on the file name plus a “suffix”. Suffixes can be defined using

the Parametric:FileNameSuffix object or if the object is not present, the default run number will be used.

In this case, suffixes have been defined for easier identification of the values entered.

Once the parametric functions have been defined within the text file via EnergyPlus, and the model has

been simulated for each of the values defined in the corresponding aspect, independent CSV files are

generated with the corresponding name for each of them.

Since this information is displayed hourly and separated by commas, it is not feasible to treat each file

independently. For this reason, it has been decided to create a code in Spyder (The Scientific Python

Development Environment) [188] through Anaconda [189].

The parametric study can be checked in more detail in Annex III.

First, in Figure 4.18, the results obtained from the parametric study on the thickness of the straw bale in

both façade and roof are shown. As it can be observed, since the total surface area of the building in terms

of external walls and roof is high, the demand in the first section of the graph, from 5 cm to 25 cm thickness,

drops drastically, softening as the thickness increases. Logically, the thicker the insulation, the better the

performance of the building. However, after 25 cm thickness, the ratio ΔTotal demand/ΔThickness is minor

and it does not make sense to increase it further for technical and economic reasons.

Figure 4.18 Straw bale thickness optimisation. Parametric study.

A similar parametric study has been carried out for the thickness of the floor insulation. The result is shown

in Figure 4.19. In this case, the variation of the insulation thickness hardly affects the performance of the

building. This is mainly due to two reasons: 1) the floor, relatively speaking, does not represent as large a

surface as the external walls or the roof, and 2) the ground temperature is more constant throughout the

year, so the heat flow in the cold months is not as high through this enclosure.


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Figure 4.19 Floor insulation thickness optimisation. Parametric study.

In a conclusion, in this case, it would be ineffective to apply this measure for the improvement of the

building, since it already has a high level of insulation, and upgrading any of the enclosures would not make

sense from an economic and energy perspective. Therefore, this measure is not applied in the optimisation

process of the straw-bale building located in Stockholm.

4.2.1.2 Valencia

The initial model simulation results (Section 4.1.1) indicate that no large efforts are needed to achieve Passive

House requirements since the starting point is close to it already. However, as there is room for

improvement, some measures are adopted to reduce even more the energy demand. To do this, results,

climate conditions and the identification of weak points have been considered to develop the following

strategies:

• Double-glazed windows – Argon gas

One of the negatively influencing factors identified in the results (Section 4.1.1) is windows. Initially, in the

building, as indicated in the construction characteristics (Section 3.3), old double-glazed windows with air

chamber have been selected, which correspond to a U-value of 2.9 W/(m2·K). Since the climate in Valencia

is not as extreme as in Stockholm, triple-glazed windows will not be necessary. However, it has been decided

to select a double-glazed window with an argon gas-tight chamber, which has better thermal properties than

air. This type of window has a thermal transmittance coefficient of 1.2 W/(m2·K) [164].

Apart from the glazed surface, frames have been also improved, since in the initial model they had 3.2

W/(m2·K). The frames selected are the same as for the building located in Stockholm; wooden frames with

a U-value of 2 W/(m2·K).


The results (Section 4.1.1) show that the influence of infiltration is high. This is due to the fact that outside

air, which is at a different temperature than the comfort temperature, enters the building in an uncontrolled

way. To achieve thermal comfort, HVAC systems consume energy to increase or decrease the air

temperature, depending on the operating mode.


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Thus, as an improvement measure, air infiltration has been reduced through an iterative process of

simulations in Cypetherm EPlus. In this way, the aim is to meet the Passive House requirements for the air

permeability of the building. Passive House Institute defines that the infiltrations must be, as maximum, 0.6

renovations per hour. After the iterative process, the improved infiltrations for each building element are

gathered in Table 4.1, while the initial ones are indicated in Table 3.16.

• Natural ventilation for cooling

In order to reduce the demand for cooling in the summer months, which is required due to the climatic

conditions in Valencia, it has been decided to implement what is known as natural cooling. Natural cooling

is based on the use of outside air during the summer nights, which is at a low temperature. In this way, using

this air as night ventilation, a cooling of the cooling demand is consequently achieved, improving the

building performance.

In Figure 4.20, the hourly temperature evolution in Valencia in the summer months could be observed. As

it can be seen, the lowest temperature each day, which is achieved during the night and early morning,

usually corresponds to comfort conditions (20ºC-26ºC). Given this outdoor temperature, it is interesting to

increase the ventilation rate in order to reduce the cooling demand this way.

Figure 4.20 Hourly dry temperature evolution in Valencia in summer months.

By means of an iterative process, it has been defined a maximum natural ventilation (windows opening) rate

of 4 l/(s·m2). Thus, the ventilation profile is the one represented in Figure 4.21, where maximum ventilation

occurs from 0 to 8 hours, which corresponds to night. After 8, natural ventilation is reduced until the usual

level, 0.8 l/(s·m2), which was the ventilation rate in the initial model to comply with legislation. In this case,

“summer” comprises from June to September, both included, in which this schedule (Figure 4.21) is applied.

Those months have been chosen according to the results obtained in the initial simulation (Section 4.1.1),

as these were the months when there was a demand for cooling. The rest of the months keep the original

constant ventilation rate of 0.8 l/(s·m2).


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Figure 4.21 Improved ventilation schedule for summer months. Natural cooling.


4.2.2.1 Stockholm

The initial rammed earth building located in Stockholm is not energy efficient as is shown in the results

(Section 4.1.2). For that reason, once results are analysed and weak points are identified, the following

improvement measures have been selected to be applied:

• Cork insulation (ETICS)

The rammed earth building, although external walls have high thermal inertia that could be useful in warmer

climates, do not have any insulation, so the conduction losses through the walls are significant. In addition,

as indicated in Section 3.3, in this type of construction technique, ETICS or an insulation layer inside the

wall is added in order to reduce the U-value of the enclosure.

In this case, to be consistent with bioconstruction principles and the use of natural building materials, a 10

cm cork panel is included as ETICS. The conductivity of this panel is 0.038 W/(m·K).

Figure 4.22 ETICS configuration for cork. Layers. [190]


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Figure 2 shows the layout of how the ETICS would be executed on the compacted earth wall. The layers

correspond to the following:

1. Support (Compacted earth)

2. Bonding mortar

3. Cork thermal Panel

4. Mechanical fixing

5. Regularisation mortar

6. Reinforcement mesh

7. Finishing mortar

8. Silicate paint

Notwithstanding, in Cypetherm EPlus, simplifications are made, since not all the layers have influence from

a thermal point of view. Thus, the external walls have been defined in the simulation software as follows

(Table 4.2 and Figure 4.23):

Table 4.2 Layers’ characteristics and thermal properties. Improved external wall. Rammed earth building in Stockholm.

Layers Thickness



Density (kg/m³)


Finishing mortar 2 0.8 0.03 1525 1000

Cork panel 10 0.038 2.63 400 1500

Bonding mortar 1 0.41 0.02 1000 1000

Compacted earth 45 1.5 0.3 1855 2085

Figure 4.23 Layer’s configuration and thermal properties. Improved external wall. Rammed earth building in Stockholm.


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The thickness optimization has been carried out through a parametric study as explained in Section 4.2.1.

The optimization results are the following (Figure 4.24):

Figure 4.24 Cork panel thickness optimisation. Parametric study in Stockholm.

Logically, the greater the insulation, the better the performance of the building and the lower the heating

demand, as can be seen in Figure 4.24. However, above a certain insulation thickness, the reduction in

demand in relation to the increase in thickness is not cost-effective. Without a full technical and economic

study, it is difficult to determine the ideal value. However, a thickness of 10 cm of cork panel has been

determined, since, from that point on, the slope of the curve is close to 0.


Ventilation has been identified as one of the weaknesses of the rammed earth building in Stockholm, as

explained in Section 4.1.2. For that reason, a highly efficient (85%) latent HRV without outdoor bypass has

been determined as a solution not to lose such a great amount of energy. The HRV characteristics are

defined and explained in more detail in Section 4.2.1.


Air infiltrations suppose high heat losses in the building due to climate conditions in Stockholm. Outdoor

temperature is low, so these uncontrolled infiltrations are negative since there is only heating demand in this

scenario.

Therefore, the building air tightness is improved according to Passive House criteria through a simulation

iterative process, obtaining the results shown in Table 4.1 in Section 4.2.1.

• Triple-glazed windows – Argon gas

Initially, windows were double-glazed windows with air chamber, as detailed in Section 3.3. In order to

improve them, they are substituted by triple-glazed windows with argon gas chamber, which have a heat

transfer coefficient of 0.9 W/(m2·K). Windows carpentry is also improved by using wooden frames with 2

W/(m2·K). For more details, Section 4.2.1.


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4.2.2.2 Valencia

As explained in results (Section 4.1.2), the rammed earth building’s performance in Valencia in the winter

months is not as good as the straw-bale building. But, in summer, energy demand is low. Therefore, the

improvement measures shown below are, most of them, oriented towards the reduction of heating demand:

• Cork insulation (ETICS)

The weakest point of the earth building is the insulation, as the exterior walls lack insulating material.

Valencia is a city with moderate temperatures, so it will not need as much insulation as in Stockholm. In

order to be in line with the use of natural materials, it has been decided to use 4 cm cork panels (k=0.038

W/m/K) as ETICS. For more information about constructive characteristics of ETICS with cork panels

and about this measure, Section 4.1.2.1.

Therefore, the external walls have been defined in Cypetherm EPlus as indicated in Table 4.3 and Figure

4.25.

Table 4.3 Layers’ characteristics and thermal properties. Improved external wall. Rammed earth building in Valencia.

Layers Thickness



Density (kg/m³)


Finishing mortar 2 0.8 0.03 1525 1000

Cork panel 4 0.038 2.63 400 1500

Bonding mortar 1 0.41 0.02 1000 1000

Compacted earth 45 1.5 0.3 1855 2085

Figure 4.25 Layer’s configuration and thermal properties. Improved external wall. Rammed earth building in Valencia.


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The thickness of the cork panel has been determined by means of a parametric study by means of the

Parametric Preprocessor of EnergyPlus, which is explained in Section 4.2.1. The thickness has been

modified from 2 cm to 20 cm, with 2 cm step simulations. The results obtained are represented in Figure

4.26:

Figure 4.26 Cork panel thickness optimisation. Parametric study in Valencia.

As it could be seen in Figure 4.26, the higher the thickness, the lower the total demand. However, increasing

thickness until a certain point could be not cost-effective, as this improvement measure is material

demanding. In addition, the initial building, as it is in Valencia (warm climate), resulted to have an acceptable

energy performance (Section 4.1.2) that can be reduced applying different measures. For that reason,

through an iterative simulation process carried out together with the other measures, a 4 cm thick cork panel

has been selected for the optimized model in the rammed earth building located in Valencia.


The ventilation initially defined in the building according to the standard is a problem in the winter months

as cold air from outside enters into the dwellings. However, the outdoor air temperature in Valencia is not

as low as in Stockholm. For this reason, it has been decided to incorporate a latent HRV in the building,

but with low efficiency (60%) in this case.

Cypetherm EPlus does not allow to have mechanical and natural ventilation at the same time. Since natural

ventilation for cooling is going to be applied, a solution to the software limitation has been adopted. An

outdoor bypass has been incorporated to be able to carry out natural ventilation at night in the summer

months so that the air does not pass through the HRV and can impair the performance of the building.

This outdoor bypass is activated when the temperature is between 18 ºC and 26ºC. These setpoint

temperatures have been defined by means of an iterative process. In this way, it is possible to avoid the

problem arising from the limitation of Cypetherm EPlus, since it interprets that in this temperature range,

the airflow has the same response as natural ventilation.

More information about the working principle of the HRV is detailed in Section 4.2.1.



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Air infiltrations are substantial from an energy point of view. For that reason, it has been decided to reduce

them until the Passive House value of 0.6 renovations per hour by means of an iterative process. Results

are shown in Table 4.1 in Section 4.2.1.

• Natural ventilation for cooling

In summer, natural ventilation (windows opening) could be positive when the outdoor temperature is close

to comfort conditions. For that reason, natural cooling through ventilation has been selected as an

improvement measure to include in the rammed earth building model. In this case, since HRV is also in

operation, an outdoor bypass (18ºC-26ºC) is included to allow it (This is the only way to define it in

Cypetherm EPlus, as explained before).

More detailed information about natural cooling through ventilation can be found in Section 4.2.1.

• Double-glazed windows – Argon gas

Windows are also placed for the rammed earth building in Valencia, by double-glazed windows with argon

gas chamber with a U-value of 1.2 W/(m2·K). Carpentry is substituted by wooden frames with 2 W/(m2·K).

More detailed information about windows substitution is in Section 4.2.1.

4.3 Energy performance optimization - Results

Building models have been optimized according to improvement measures applied, as indicated in Section

4.2. In the following sections, results about the energy performance of optimized buildings are shown and

analysed. The optimisation has been carried out with the aim, if possible, of achieving the Passive House

criteria of 15 kWh/(m2·K) for heating and cooling, respectively. However, this should be achieved without

changing the shape of the building and/or the distribution of the glazed surface, which has not been possible

in all scenarios.

4.3.1 Straw-bale building

4.3.1.1 Stockholm

Once the appropriate improvement measures have been applied to the straw bale building model at the

Stockholm location, the annual energy and power demand results are as shown in Figure 4.27.

Figure 4.27 Annual energy and capacity of the improved straw-bale building in Stockholm.


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the improved straw-bale building located in Stockholm:



As can be seen, despite having implemented all the improvement measures specified in Section 2, the target

of 15 kWh/(m2·K) for heating and cooling has not been achieved. Given the climatic conditions in

Stockholm, it is not trivial to reduce the energy demand to such demanding values. Therefore, in order to

further reduce the demand, geometrical modifications (building shape, glazing surface, etc.) would be

needed.

Nonetheless, heating demand has been reduced by 118.29 kWh/(m2·K), while cooling demand has been

consequently increased by 9.22 kWh/(m2·K). This results in a total demand reduction of 77.8% thanks to

the improvement measures implementation.

In Figure 4.28, the annual energy balance of the improved straw-bale building located in Stockholm is

represented. Heat flow related to opaque enclosures and ventilation and infiltrations is still significant.

Nevertheless, insulation in walls, roof, or floors could be hardly improved since thicknesses of straw-bales

and floor insulation are already optimized. On the other hand, concerning ventilation, a highly efficient

HRV has been implemented, and not much more can be done in this respect since ventilation is compulsory

from a health perspective. Infiltrations have been highly minimized, until Passive House air renovations per

hour requirement.

Apart from that, cooling demand could be reduced by implementing shadowing in windows or through

natural ventilation in the summer months. However, since cooling demand is already low, it has been

reconsidered not to apply those passive measures in this scenario.

Figure 4.28 Annual energy balance of the improved straw-bale building in Stockholm.


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4.3.1.2 Valencia

Once the improvement measures have been applied to the straw-bale building model of Valencia, simulation

can be carried out. The results related to demanded energy and capacity are obtained, as shown in Figure

4.29.

Figure 4.29 Annual energy and capacity of the improved straw-bale building in Valencia.


the improved straw-bale building located in Valencia:



As predicted, given the results of the energy simulation of the initial model and given the climatic conditions

of the Spanish city, the values required by Passive House in terms of heating and cooling demand have been

achieved. Efforts in terms of passive measures, to reduce the demand to this level, have been limited,

considering the starting point of the initial building performance. This indicates that further reductions in

demand could be achieved if desired through the application of other passive strategies.

Notwithstanding, heating and cooling demand have been reduced by 6.06 kWh/(m2·year) and by 7.38

kWh/(m2·year), respectively. This results in a total demand reduction of 36.3% after applying the different

improvement measures.

Figure 4.30 shows the thermal balance obtained after the simulation of the improved model. Despite the

reduction of air infiltration in the building, ventilation is still important in terms of energy balance. To

further improve the model, an HRV could be incorporated to operate in the winter months, thereby

reducing the heating demand. In summer, natural ventilation is already taking place at night, so the HRV

could be switched off during these times as the ventilation ratio would already be met non-mechanically.

As for the cooling demand, shading of the windows during the critical hours of the summer months would

be chosen in this case to further reduce consumption. Figure 4.30 shows the importance of heat flow

through the windows, which could be avoided if desired by means of blinds, awnings, overhangs, or other

shadowing elements.


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Figure 4.30 Annual energy balance of the improved straw-bale building in Valencia.


4.3.2.1 Stockholm

After several optimization measures included in the initial model of the rammed earth building in

Stockholm, the results concerning energy and power demand throughout the year are represented in the

graphs in Figure 4.31. At first glance, it can be seen that the demand for heating and cooling is unbalanced,

with the former being much higher, comprising the period from October to April. There is no demand for

air conditioning in May, June, and September, which is one of the big differences with respect to the straw-

bale building, being the thermal transmittance of the walls higher in the earthen house. Therefore, the earth

building, with its higher inertia, would perform much better in climates with an average temperature close

to comfort conditions.


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Figure 4.31 Annual energy and capacity of the improved rammed earth building in Stockholm.


the improved rammed earth building located in Stockholm:



However, looking at the normalized annual values, it can be observed that, in spite of applying several

improvement strategies, the Passive House requirements, which are 15 kWh/(m2·year) for cooling and

heating, have not been achieved. This could be probably solved by changing the whole design of the building

in terms of geometry and window distribution, but it is not allowed in this study, as already explained.

Nevertheless, despite not having achieved the demand reduction target, the demand has been reduced to a

large extent, as initially, the heating demand was more than 300 kWh/(m2·year). Thus, the heating demand

has been reduced by 263 kWh/(m2·year), with a slight increase in cooling demand, which was initially zero.

This translates into a reduction of the total demand of the HVAC systems by 86.3% compared to the initial

model.

Analysing the annual energy balance of the rammed earth building in Stockholm (Figure 4.32), it can be

concluded that the heat flow released by conduction through opaque enclosures is still high. However, the

insulation thickness has been optimized and further improvement does not make sense from a techno-

economic perspective. The main reason why this heat flow is so high is the temperature difference between

indoor and outdoor the building, which is in certain moments over 30ºC.

The most important possible improvement measures for the reduction of heating demand have been

considered, analysed and, if necessary, applied to the model, but even so, it has not been possible to further

reduce consumption. Therefore, it can be concluded that, for a climate like Stockholm, in order to have a

building that meets the Passive House criteria and has the current constructive characteristics, it must have

a geometry that favours solar gain through the glazed surfaces in the winter months, and also have a high

level of thermal insulation in the envelope.


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Figure 4.32 Annual energy balance of the improved rammed earth building in Stockholm.

4.3.2.2 Valencia

Once applied the improvement strategies in the initial model of the rammed earth building in Valencia,

simulations are carried out in Cypetherm EPlus. Results, as in previous sections, are shown in terms of

demanded energy and capacity in Figure 4.33. As in the earth house in Stockholm, there are certain months

when there is no demand for heating and cooling, again showing that in the months when the temperature

is neither high nor low, thermal inertia has an appreciable advantage. However, if temperatures are not ideal

during the rest of the year, insulation is required to ensure a good performance of the building in terms of

comfort and demand.

Figure 4.33 Annual energy and capacity of the improved rammed earth building in Valencia


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the improved rammed earth building located in Valencia:



The normalized values show that after applying some measures (more than in the straw-bale house in

Valencia), the Passive House criteria referred to as energy demand is achieved. The heating and cooling

demand have been reduced by 55.6 kWh/(m2·year) and by 2.56 kWh/(m2·year), respectively. As regards the

total demand, by applying the passive strategies, it has been reduced by 73.9%.

In this case, the main heat flow, as could be seen in Figure 4.34, corresponds to the heat released through

the opaque enclosures, but it does not suppose any problem since the highest demand is for cooling. For

that reason, a further improvement that has not been implemented is the windows shadowing in summer

when solar gains through them result in an important heat flow in the energy balance. This could be done

either by blinds, overhangs, or similar solutions.

Figure 4.34 Annual energy balance of the improved rammed earth building in Valencia.

4.4 Results Comparison

Throughout Chapter 4, the results obtained from the energy simulations of the different models have been

shown and analysed. In total, the results of 8 different simulations have been analysed: 4 simulations of the

initial models of both the straw-bale and rammed earth buildings, for the two selected climates, Stockholm

and Valencia, and 4 simulations corresponding to the optimizations of the initial models. The summary of

the results obtained for each of the scenarios, in terms of energy demand (heating and cooling) and demand

reduction once the improvement measures have been applied, is presented in Table 4.4.


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Table 4.4. Energy demand summary. Initial and optimized models.

Scenario Straw-bale Building Rammed earth building

Stockholm Valencia Stockholm Valencia

Initial Model

Heating demand (kWh/(m2·year))

140.00 20.10 301.82 61.59

Cooling demand (kWh/(m2·year))

0.22 16.95 0.00 17.07

Total demand (kWh/(m2·year))

140.22 37.05 301.82 78.66

Optimized Model

Heating demand (kWh/(m2·year))

21.71 14.04 38.15 5.99

Cooling demand (kWh/(m2·year))

9.42 9.57 3.22 14.51

Total demand (kWh/(m2·year))

31.13 23.61 41.37 20.5

Total Demand Reduction 77.8% 36.3% 86.3% 73.9%

Overall, as can be seen in Table 4.4, the straw bale building is more efficient than the earth building in both

climates. In the winter months, when the outside temperature is below the comfort temperature, the straw

bale building, which is more insulated than the earth building, performs substantially better. In fact, the

heating demand in the earth building is 2 times higher than that of the thatched building in both Stockholm

and Valencia, as can be seen in row 1 of Table 4.4.

On the other hand, as for the cooling demand of the initial models, it is almost identical for the two

buildings. In the case of Stockholm, since temperatures are low throughout the year, there is hardly any

need for the operation of the cooling equipment throughout the year. If one looks, in contrast, at the

buildings located in Valencia, it can be seen that the demand is very similar, which leads to the conclusion

that the insulation of the building envelope does not play such an important role as it does in winter. The

total demand of the two buildings clearly shows the predominance of the thatched building over the earth

building in terms of thermal behaviour in both climates.

Regarding the energy optimization of the scenarios, the results that have been obtained, in the case of

Stockholm, do not meet the Passive House criteria in the heating demand department, both for the straw-

bale building and the earth building, the latter being further away from the target of 15 kWh/(m2·year).

Further reduction in demand has not been achieved, due to the restrictions imposed on the modification of

the building geometry and windows to maintain consistency with the initial building. On the other hand,

the models of both buildings, simulated in Valencia, once optimized, comply with the requirements

established by Passive House in terms of energy demand, with just over 20 kWh/(m2·year) of total demand.

In any case, the efforts made in the earth building have been much greater, from the point of view of

optimisation. In the earthen models, a larger number of passive measures have been applied to achieve the

energy reduction that can be seen in Table 4.4. This factor must be taken into account in the comparison

of the results.

Apart from that, after the application of the improvement measures explained in Section 4.2, a large

reduction of the total demand has been achieved for all models. The reduction of the total demand is above

70% in all scenarios except for the straw-bale building located in Valencia. The reason why this reduction

in consumption is only 36.3% is that the starting point was favourable, and it was not necessary to reduce


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the demand very much to reach the demanding values imposed by Passive House. However, greater efforts

could have been made to reduce demand even further if this had been desired.

Regardless of whether the Passive House criteria have been met, it can be concluded that these buildings,

modelled and simulated with the use of natural materials, are highly efficient from a thermal and energy

point of view, with the correct application of improvement measures depending on the constructive

characteristics of the buildings and the climatic conditions.

But the analysis must go beyond the annual demand values. Since one of the objectives of this project is the

evaluation of the thermal inertia as a decisive parameter for the thermal aspect and the functioning of the

building, its influence needs to be assessed. It has already been shown that, in annual terms, the earth

building (high inertia) performs worse than the straw building (low inertia). However, by analysing the

evolution of the energy demand in all scenarios (Section 4.1 and Section 4.3) a pattern can be observed in

the spring and autumn months (warm temperature), especially in the optimised models, where the heating

and cooling consumption is zero for the high inertia building and not for the low inertia building. Through

an iterative process of simulations, acting on the density and specific heat of the earth, increasing and

decreasing the thermal inertia, it has been seen to have an influence in those months when the average

temperature is close to comfort conditions. Thermal inertia in these months is beneficial as the walls absorb

the heat by retaining it and dampening the heatwave due to the daily temperature change. However, at least

in the simulated climates, it does not make a big change to the overall performance of the building. The

results of the inertia study show that only a change of at most 5 kWh/(m2·year) is experienced, for the

climates studied. Nevertheless, the potential of thermal inertia has been observed, and its study in other

climates, where the temperature is constant throughout the year, and varying daily temperatures averaging

around comfort temperatures, could be of great interest. However, a more in-depth study should be carried

out given the complexity of this thermal property of materials. Thermal inertia can be defined in different

ways [191], but thermal effusivity is the one adopted in the current research.

4.4.1 Environmental and Economic assessment

In addition to the results related to energy demand, the environmental and economic aspect has also been

assessed, in terms of GHG emissions in ton CO2 and energy costs in €, respectively on an annual basis.

The price of electricity in Sweden and Spain are 0.1718 €/kWh and 0.2298 €/kWh, respectively, according

to the European Commission [192], as represented in Figure 4.35. Also, according to the IEA [160], the

GHG emissions attached to the Spanish energy mix is 1.9 ton CO2/toe (Figure 4.36), and in Sweden, it is

0.7 ton CO2/toe (Figure 4.37).

Figure 4.35. Electricity prices (including taxes) for household consumers in different countries. Second half 2020 [192].


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Figure 4.36 CO2 intensity of energy mix in Spain 1990-2019 [160].

Figure 4.37 CO2 intensity of energy mix in Sweden 1990-2019 [160].

Taking into account the total demand values obtained above, which are listed in Table 4.4, as well as the

economic and environmental factors, the following annual energy cost and GHG emission values have been

obtained for each of the buildings, on an absolute non-normalised basis (Table 4.5). Also, the HVAC system

technology considered is a heat pump with an annual coefficient of performance (COP1) of 3 for heating

and COP2 of 2 for cooling, respectively:

Table 4.5 Total energy cost and GHG emissions of the buildings and reduction after optimization.

Scenario Straw-bale Building Rammed earth building

Stockholm Valencia Stockholm Valencia

Initial Model

Total Energy Cost (€/year)

8,946 3,882 19,241 7,435

GHG Emissions (ton CO2/ year)

3.13 2.76 6.74 5.29

Optimized Model

Total Energy Cost (€/year)

2,284 2,421 2,740 2,366

GHG Emissions (ton CO2/ year)

0.80 1.72 0.96 1.68

Energy Cost Reduction (€/year) 6,661 1,460 16,501 5,068

GHG Emissions Reduction (ton CO2/ year)

2.33 1.04 5.78 3.60


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Electricity prices and emissions attached to electricity in Sweden are lower than in Spain. Notwithstanding,

Energy demand in Stockholm is higher. Therefore, in the initial models, where the difference in energy

demand between both countries is larger, the economic and environmental performances of the buildings

located in Stockholm are worse. However, after optimization is applied, for the straw-bale building, the

economic expense is higher in Valencia than in Stockholm. In regard to GHG emissions, in the optimized

models, the buildings located in Stockholm are less emitting than the ones located in Valencia since the

energy mix in Sweden is more environmentally responsible.

Energy cost reduction is also calculated for all the scenarios. The greatest reduction in energy costs and

emissions was achieved in the rammed earth building in Stockholm, which was, after all, the scenario where

the greatest reduction in total demand was obtained.


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5 Conclusions

The purpose of the current project is to provide information on construction with natural materials and to

demonstrate their suitability for the construction sector, as a solution in line with the long-term strategy of

the EU 2050. Thus, the research aims to conduct a literature review on sustainable construction with natural

materials and to evaluate individual case studies. These case studies correspond to two buildings, using straw

bales and compacted earth, respectively, as main materials, which are simulated in Stockholm and Valencia.

The reason why these two materials have been selected is that they have been identified as suitable for

construction due to their technical characteristics and their resource availability over a large part of the

Earth's surface. On the other hand, straw and earth have different thermal properties that are intended to

be evaluated from an energy point of view, since straw has low conductivity and thermal inertia, while earth

has high conductivity and thermal inertia. Therefore, through the current study, the influence of thermal

inertia on the thermal performance of buildings in the studied climates is evaluated. Valencia and Stockholm

have been selected because the aim is to demonstrate how high energy efficiency can be achieved by using

these natural materials in different climates through the optimisation of buildings.

This has been done by means of extensive state of the art study on energy efficiency and natural materials,

gathering valuable information from other studies, and identifying research gaps. The assessment of the

energy performance of the buildings has been carried out for each of the four scenarios, corresponding to

the buildings with the different materials and the two climates (deeply analysed), using Cypetherm EPlus.

Additionally, these models have been energy optimised by implementing improvement measures, taking the

Passive House criteria as a reference, depending on their initial construction characteristics and climatic

conditions. In the process of optimising the buildings, the imperative need for the use of heat recovery

ventilation, as well as the use of a high level of insulation in opaque enclosures, has been identified in

Stockholm. In Valencia, the use of insulation is necessary, at a lower level, but the use of a heat recovery

unit for ventilation is not.

Total energy demand to maintain thermal comfort inside the building has been obtained for the straw-bale

building of 140.22 kWh/(m2·year) in the case of Stockholm and 37.05 kWh/(m2·year) in the case of

Valencia. On the other hand, for the earth building, a total demand of 301.82 kWh/(m2·year) has been

obtained in Stockholm and 78.66 kWh/(m2·year) in Valencia. Clearly, the buildings located in Valencia have

a better thermal performance than those in Stockholm. This is mainly due to the climatic conditions of both

locations, as Valencia has more moderate temperatures. Furthermore, the straw bale building, having a lower

heat transfer coefficient in the building envelope, performs better in both climates, especially in terms of

cooling demand. Once improvement measures are applied, a reduction in demand for the straw bale building

of 77.8% and 36.3% has been achieved for Stockholm and Valencia, respectively. In the earth building, after

the application of the improvement measures, the demand has been reduced by 86.3% in Stockholm and

73.9% in Valencia. Other improvement measures, not involving modification of the building geometry, such

as improving the permeability of the building, replacement of windows, or night ventilation for cooling,

have been applied in the models according to their needs.

In Stockholm, despite the application of appropriate passive measures and the energy efficiency achieved,

the demand values required by Passive House have not been met. It has been concluded that in order to

achieve these values, a different geometrical design of the building should be adopted, as well as an optimised

distribution of the windows. However, the national legislation from Sweden and Spain has not been

assessed, whose criteria may be accomplished.

Apart from that, better performance of the straw bale building compared to the rammed earth building has

been observed, due to the low conductivity of the straw. This partly demonstrates that in the climates

studied, the influence of thermal inertia is not important from an energy efficiency point of view. This has

also been demonstrated by iterative simulations, modifying the thermal inertia, and observing its slight

influence on the overall demand of the buildings in the climates studied. However, a variation in the thermal

behaviour of the building has been observed from month to month, showing that inertia could be interesting


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in climates with a more constant annual temperature and varying daily temperatures close to comfort

conditions.

This study proves that, from an energy perspective, natural materials can be used in high-efficiency buildings

in different climates. In order to do this, buildings must be designed adapting to the environment in

accordance with the corresponding climatic conditions and with the natural materials used and their

characteristics.

5.1 Future work

Apart from the present energy study, an environmental impact study (such as an LCA) of buildings

constructed with these natural materials would have been of great interest. In this way, not only the great

thermal characteristics of these materials would have been demonstrated, but also the environmental

impacts, in terms of GHG or other pollutants emissions, over the whole life of the building would have

been assessed. This, if it were included in the thesis, would show how environmentally beneficial the use of

natural materials would be compared to conventional materials. However, to carry out this study, a wealth

of information would be needed, such as the location of the raw materials, the amount of each material, the

lifetime of the building, the end of life of the building, construction practices, and energy used on it…

In accordance with this, a Life Cycle Cost (LCC) could be included in a further stage of the project, detailing

the price of each stage of the project, including the construction and the materials. Notwithstanding, this

would require information about the production process which was not possible to obtain in this master

thesis.

In addition, a larger number of climates could be simulated with the two building typologies. Furthermore,

a more in-depth study on the thermal inertia of the earth could be the subject of a future study, where its

influence could be seen in a climate with more constant temperatures throughout the year. Better

performance of the rammed earth building is expected despite the lack of insulation.


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6 Bibliography

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[2] V. Reverte, X. Masip, C. Prades-Gil, P. Carnero-Melero, F. Barceló-Ruescas, and J. R. Clausell, “Calibration with real measurements of a straw-bale passive building model,” CYTEF 2020 − X Congr. Ibérico | VIII Congr. Iberoam. las Ciencias y Técnicas del Frío, pp. 1–3, 2020.

[3] “Passivhaus Institut.” [Online]. Available: https://passivehouse.com/. [Accessed: 23-Jan-2020].

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Description of the linear thermal bridges

EN ISO 14683

EN ISO 10211

FreeText

Annex I

Private

Length(m)

Y(W/(m·K))

TFi [E]ground floor-[E]ground floor(180)-[C]Partition(90)

Frentes de forjado con continuidad del aislamiento de fachada205.049 0.04

LFi [E]ground floor-[B]External wall(90)

Suelos en contacto con el terreno con continuidad entre el aislamiento de fachada yde solera

77.407 0.21

TW [C]Partition-[C]Partition(90)-[C]Partition(180)


TW [B]External wall-[B]External wall(180)-[C]Partition(90)


LWi [B]External wall-[B]External wall(90)

Esquinas entrantes (al interior)51.264 -0.07

TW [C]Partition-[B]External wall(90)-[B]External wall(180)


LWi [C]Partition-[C]Partition(90)

Esquinas salientes (al exterior)153.792 0.05



CFs [F]Internal floor-[C]Partition(90)-[F]Internal floor(90)-[C]Partition(90)


TFms [F]Internal floor-[B]External wall(90)-[B]External wall(180)


Wi [K]2.4x1.5-[B]External wall

Alfeizares con continuidad entre el aislamiento de fachada y la carpintería48.000 0.08

Ws [K]2.4x1.5-[B]External wall

Dinteles con continuidad entre el aislamiento de fachada y la carpintería48.000 0.13

Wl [K]2.4x1.5-[B]External wall

Jambas con continuidad entre el aislamiento de fachada y la carpintería30.000 -0.01



LWo [C]Partition-[C]Partition(90)


CW [C]Partition-[C]Partition(90)-[C]Partition(90)-[C]Partition(90)


Wi [K]1x1.2-[B]External wall


Ws [K]1x1.2-[B]External wall


Wl [K]1x1.2-[B]External wall


LWo [B]External wall-[B]External wall(90)


TFmi [F]Internal floor-[B]External wall(90)-[B]External wall(180)


Page 2 - 4

Length(m)

Y(W/(m·K))

CFi [F]Internal floor-[C]Partition(90)-[F]Internal floor(90)-[C]Partition(90)


GF2

Cubiertas planas con continuidad entre el aislamiento de fachada y el de cubierta77.407 0.23

TFs [G]Flat roof-[G]Flat roof(180)-[C]Partition(90)


Page 3 - 4

corridor

Length(m)

Y(W/(m·K))























5.328 0.21



GF2




Page 4 - 4

Private

Length(m)

Y(W/(m·K))





77.407 0.21





LWi [B]External wall-[B]External wall(90)

Esquinas entrantes (al interior)51.264 -0.07



LWi [C]Partition-[C]Partition(90)








Wi [K]2.4x1.5-[B]External wall


Ws [K]2.4x1.5-[B]External wall


Wl [K]2.4x1.5-[B]External wall




LWo [C]Partition-[C]Partition(90)


CW [C]Partition-[C]Partition(90)-[C]Partition(90)-[C]Partition(90)








LWo [B]External wall-[B]External wall(90)




Page 2 - 4

Length(m)

Y(W/(m·K))



GF2




Page 3 - 4

corridor

Length(m)

Y(W/(m·K))























5.328 0.21



GF2




Page 4 - 4

Condensation

UNE EN ISO 13788

FreeText

Annex II

INDEX

1. PRIVATE....................................................................................................................... 3

1.1. External wall...................................................................................................... 3

1.1.1. Condensation analysis results........................................................................ 3

1.1.2. Hygrothermal design conditions..................................................................... 3

1.1.3. Description of the construction element.......................................................... 4

1.1.4. Calculation of the internal surface temperature required to avoid the criticalsurface humidity.......................................................................................... 4

1.1.5. Interstitial condensation calculation............................................................... 5

1.1.6. Graphical representation of the foreseen interstitial condensation...................... 6

1.2. Flat roof.............................................................................................................. 6







1.3. ground floor........................................................................................................ 10







PRIVATE

1.1. External wall

1.1.1. Condensation analysis results

1.1.1.1. Surface condensation

fRsi = 0.946 ≥ fRsi,min = 0.338The construction element does not show any signs of surface condensation.

where:

fRsi: Internal surface resistance factor, calculated as (1 - U·Rsi), where U = 0.214 W/m²·K and Rsi = 0.25 m²·K/W.

fRsi,min: Minimum internal surface resistance factor, required to avoid the critical surface humidity, calculated using a value of φsi,cr ≤0.8.

1.1.1.2. Interstitial condensation

The construction element does not show any sign of interstitial condensation.

1.1.2. Hygrothermal design conditions

The internal and external hygrothermal conditions used to carry out the condensation calculations are thefollowing:

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0

Relative humidity, φe (%) 50 50 50 50 50 50 50 50 50 50 50 50

Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0

Relative humidity, φi (%) 60 60 60 60 60 60 60 60 60 60 60 60

The psychrometric diagram associated with the location, with a height above sea level of 0 m, is displayedbelow. Represented using straight line segments are the transitions from each external design condition toits corresponding internal condition.

Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24

Condensation

Page 3 - 14

1.1.3. Description of the construction element

Below is the section diagram of the composition of the construction element:

1 2 3 4 5

Exte

rnal

Inte

rnal

The thermal properties and water vapour diffusion properties of the homogenous layers of the parallel sidesmaking up the design model of the construction element are as follows:

External wall e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.04

1 Pine Wood C24 3.0 0.130 0.23077 20 0.6

2 Air gap 2.5 0.09000 0.01

3 Wood Fiber TOP220 2.5 0.050 0.50000 20 0.5

4 Straw bale 25.0 0.071 3.51124 1 0.25

5 Ecoclay 4.0 0.240 0.16667 10 0.4

Rsi 0.13where:

e: Thickness, cm.

λ: Thermal conductivity of the material, W/(m·K).

R: Thermal resistance of the material, m²·K/W.

μ: Water vapour diffusion resistance factor of the material.

Sd: Equivalent air thickness against the water vapour diffusion, m.

Rse: External surface thermal resistance of the element, m²·K/W.

Rsi: Internal surface thermal resistance of the element, m²·K/W.

The design information regarding the hygrothermal parameters of the complete element, derived from thehomogenous layer model, is the following:

Magnitude Units Value

Total thickness of the element, eT cm 37.0

Total thermal resistance, RT m²·K/W 4.6687

Total equivalent air thickness, Sd,T m 1.76

Thermal transmittance, U W/(m²·K) 0.214

Internal surface resistance factor, fRsi -- 0.946where:

ET: Total thickness of the element, cm.

RT: Total thermal resistance of the element, sum of the thermal resistance of each layer, including surface resistances Rse and Rsi,m²·K/W.

SdT: Total equivalent air thickness, sum of the equivalent thickness of each layer of the element, m.

U: Thermal transmittance of the element, calculated as the inverse of the total thermal resistance, W/(m²·K).


1.1.4. Calculation of the internal surface temperature required to avoid the critical surfacehumidity

With the aim to prevent the adverse affects of the critical surface humidity, the maximum relative humidityon the internal surface has been limited to a value of φsi,cr ≤ 0.8.

Condensation

Page 4 - 14

Given the external and internal hygrothermal conditions, fRsi,min is calculated as follows:

θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:

θe: External air temperature, °C.

φe: Relative humidity of the external air, %.

θi: Internal air temperature, °C.

φi: Relative humidity of the internal air, increased by a safety coefficient 5%, %.

Pi: Vapour pressure in the internal air, Pa.

Psat(θsi): Minimum acceptable water vapour saturation pressure for the internal surface, Pa.

θsi,min: Minimum acceptable internal surface temperature, calculated based on the minimum acceptable saturation pressure, °C.

fRsi,min: Minimum internal surface resistance factor.

Given that fRsi = 0.946 > fRsi,min = 0.338, no surface condensation occurs in the construction element.

1.1.5. Interstitial condensation calculation

Displayed below are the results obtained in the analysis of the temperatures and pressures at eachinterface of the homogenous layers making up the design model of the construction element.

Calculation of the interstitial condensation in the month of January.

External wall θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0

External surface 15.04 1709.113 852.204 49.9 -- --

Interface 1-2 15.29 1736.487 1039.692 59.9 -- --

Interface 2-3 15.39 1747.267 1042.817 59.7 -- --

Interface 3-4 15.92 1808.229 1199.058 66.3 -- --

Interface 4-5 19.68 2291.384 1277.178 55.7 -- --

Internal surface 19.86 2316.887 1402.171 60.5 -- --

Internal air 20.00 2336.951 1402.171 60.0where:

θ: Temperature, °C.

Psat: Water vapour saturation pressure, Pa.

Pn: Water vapour pressure, Pa.

φ: Relative humidity, %.

gc: Condensation flow density, g/(m²·month).

Ma: Accumulated humidity content per unit area, g/m².>> Graphical representation (January)

Condensation

Page 5 - 14

1.1.6. Graphical representation of the foreseen interstitial condensation

January

1 2 3 4 5-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22

Pressure (Pa) Temperature (°C)

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Thickness (m)Theoretical vapour pressure Real vapour pressure

Saturation pressure Temperature

1.2. Flat roof




where:







Condensation

Page 6 - 14


External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0


Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0



Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24



1 23 4 5 6 7

Exte

rnal

Inte

rnal


Condensation

Page 7 - 14

Flat roof e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.04

1 Sand and Gravel 10.0 2.000 0.05000 50 5

2 Ethylene Propylene Diene M-class [EPDM] 0.2 0.250 0.00800 6000 12

3 Oriented Strand Board [OSB] 2.2 0.130 0.16923 30 0.66

4 Air gap 10.0 0.21320 0.01


6 Straw bale 25.0 0.071 3.51124 1 0.25


Rsi 0.10where:

e: Thickness, cm.






















θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

Condensation

Page 8 - 14

θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:













Flat roof θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0


Interface 1-2 15.10 1715.585 995.126 58.0 -- --

Interface 2-3 15.11 1716.581 1338.141 78.0 -- --

Interface 3-4 15.30 1737.784 1357.007 78.1 -- --

Interface 4-5 15.54 1764.822 1357.293 76.9 -- --

Interface 5-6 15.73 1786.545 1376.159 77.0 -- --

Interface 6-7 19.70 2293.355 1383.305 60.3 -- --









Condensation

Page 9 - 14


January

1 23 4 5 6 7-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22


-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6



1.3. ground floor




where:







Condensation

Page 10 - 14


External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0


Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0



Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24



1 2 3 4 5 6

Exte

rnal

Inte

rnal


Condensation

Page 11 - 14

ground floor e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.00

1 Polipropilene [PP] 0.2 0.220 0.00909 10000 20

2 Pine Wood C24 2.2 0.130 0.16923 20 0.44

3 Floor insulation 8.0 0.038 2.10526 1 0.08



6 Pine Wood C24 2.2 0.130 0.16923 20 0.44

Rsi 0.17where:

e: Thickness, cm.






















θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

Condensation

Page 12 - 14

θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:













ground floor θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0


Interface 1-2 15.02 1706.189 1116.484 65.4 -- --

Interface 2-3 15.32 1739.648 1122.298 64.5 -- --

Interface 3-4 19.08 2206.609 1123.355 50.9 -- --

Interface 4-5 19.38 2248.511 1132.076 50.3 -- --

Interface 5-6 19.39 2250.781 1396.357 62.0 -- --









Condensation

Page 13 - 14


January

1 2 3 4 5 6-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22


-0.05 0.00 0.05 0.10 0.15 0.20



Condensation

Page 14 - 14

INDEX

1. PRIVATE....................................................................................................................... 3

1.1. External wall...................................................................................................... 3







1.2. Flat roof.............................................................................................................. 6







1.3. ground floor........................................................................................................ 10







PRIVATE

1.1. External wall




where:








External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0


Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0



Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24

Condensation

Page 3 - 14



1 2 3 4 5

Exte

rnal

Inte

rnal


External wall e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.04

1 Pine Wood C24 3.0 0.130 0.23077 20 0.6

2 Air gap 2.5 0.09000 0.01

3 Wood Fiber TOP220 2.5 0.050 0.50000 20 0.5

4 Straw bale 25.0 0.071 3.51124 1 0.25

5 Ecoclay 4.0 0.240 0.16667 10 0.4

Rsi 0.13where:

e: Thickness, cm.





















Condensation

Page 4 - 14


θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:













External wall θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0


Interface 1-2 15.29 1736.487 1039.692 59.9 -- --

Interface 2-3 15.39 1747.267 1042.817 59.7 -- --

Interface 3-4 15.92 1808.229 1199.058 66.3 -- --

Interface 4-5 19.68 2291.384 1277.178 55.7 -- --









Condensation

Page 5 - 14


January

1 2 3 4 5-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22


-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45



1.2. Flat roof




where:







Condensation

Page 6 - 14


External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0


Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0



Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24



1 23 4 5 6 7

Exte

rnal

Inte

rnal


Condensation

Page 7 - 14

Flat roof e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.04

1 Sand and Gravel 10.0 2.000 0.05000 50 5

2 Ethylene Propylene Diene M-class [EPDM] 0.2 0.250 0.00800 6000 12


4 Air gap 10.0 0.21320 0.01


6 Straw bale 25.0 0.071 3.51124 1 0.25


Rsi 0.10where:

e: Thickness, cm.






















θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

Condensation

Page 8 - 14

θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:













Flat roof θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0


Interface 1-2 15.10 1715.585 995.126 58.0 -- --

Interface 2-3 15.11 1716.581 1338.141 78.0 -- --

Interface 3-4 15.30 1737.784 1357.007 78.1 -- --

Interface 4-5 15.54 1764.822 1357.293 76.9 -- --

Interface 5-6 15.73 1786.545 1376.159 77.0 -- --

Interface 6-7 19.70 2293.355 1383.305 60.3 -- --









Condensation

Page 9 - 14


January

1 23 4 5 6 7-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22


-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6



1.3. ground floor




where:







Condensation

Page 10 - 14


External conditions

Temperature, θe (°C) 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0


Internal conditions

Temperature, θi (°C) 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0



Hum

idity

ratio

, w(g

/kg)

Temperature, T(°C)

-15 -10 -5 0 5 10 15 20 25 30 35 40 450

2

4

6

8

10

12

14

16

18

20

22

24



1 2 3 4 5 6

Exte

rnal

Inte

rnal


Condensation

Page 11 - 14

ground floor e(cm)

λ(W/m·K)

R(m²·K/W)

μ Sd

(m)

Rse 0.00


2 Pine Wood C24 2.2 0.130 0.16923 20 0.44

3 Floor insulation 8.0 0.038 2.10526 1 0.08



6 Pine Wood C24 2.2 0.130 0.16923 20 0.44

Rsi 0.17where:

e: Thickness, cm.






















θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

January 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

February 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

March 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

April 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

May 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

June 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

July 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

August 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

September 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

October 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

November 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338

Condensation

Page 12 - 14

θe

(°C)φe

(%)θi

(°C)φi

(%)Pi

(Pa)Psat (θsi)

(Pa)θsi,min

(°C)fRsi,min

December 15.0 50.0 20.0 65.0 1519.02 1898.77 16.7 0.338where:













ground floor θ(°C)

Psat

(Pa)Pn

(Pa)φ

(%)gc

(g/(m²·month))Ma

(g/m²)

External air 15.00 1704.407 852.204 50.0


Interface 1-2 15.02 1706.189 1116.484 65.4 -- --

Interface 2-3 15.32 1739.648 1122.298 64.5 -- --

Interface 3-4 19.08 2206.609 1123.355 50.9 -- --

Interface 4-5 19.38 2248.511 1132.076 50.3 -- --

Interface 5-6 19.39 2250.781 1396.357 62.0 -- --









Condensation

Page 13 - 14


January

1 2 3 4 5 6-200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-2

0

2

4

6

8

10

12

14

16

18

20

22


-0.05 0.00 0.05 0.10 0.15 0.20



Condensation

Page 14 - 14

Condensation

UNE EN ISO 13788

FreeText

Annex III

Rectangle

FreeText

Parametric study. Parametric Preprocessor and Python.

Rectangle

2

• Straw bale thickness:

By means of the EnergyPlus Parametric Preprocessor the following code has been added to the text file:

Parametric:FileNameSuffix, Names, !- Name E_straw_0.05, !- Suffix for File Name in Run 1 E_straw_0.10, !- Suffix for File Name in Run 2 E_straw_0.15, !- Suffix for File Name in Run 3 E_straw_0.20, !- Suffix for File Name in Run 4 E_straw_0.25, !- Suffix for File Name in Run 5 E_straw_0.30, !- Suffix for File Name in Run 6 E_straw_0.35, !- Suffix for File Name in Run 7 E_straw_0.40, !- Suffix for File Name in Run 8 E_straw_0.45, !- Suffix for File Name in Run 9 E_straw_0.50; !- Suffix for File Name in Run 10 Parametric:SetValueForRun, $e_straw, !- Name 0.05, !- Value for Run 1 0.10, !- Value for Run 2 0.15, !- Value for Run 3 0.20, !- Value for Run 4 0.25, !- Value for Run 5 0.30, !- Value for Run 6 0.35, !- Value for Run 7 0.40, !- Value for Run 8 0.45, !- Value for Run 9 0.50; !- Value for Run 10 Material, M15_Straw_bale (250mm), !- Name Rough, !- Roughness =$e_straw, !- Thickness {m} 0.0712, !- Conductivity {W/m-K} 130, !- Density {kg/m3} 1000, !- Specific Heat {J/kg-K} 0.9, !- Thermal Absorptance 0, !- Solar Absorptance 0.6; !- Visible Absorptance

3

• Floor insulation thickness:

For the floor insulation parametric study, the following code has been added to the file text of the model

in EnergyPlus Parametric Preprocessor:

Parametric:FileNameSuffix,

Names, !- Name

E_floor_ins_0.02, !- Suffix for File Name in Run 1









E_floor_ins_0.20; !- Suffix for File Name in Run 10

Parametric:SetValueForRun,

$e_floor_ins, !- Name

0.02, !- Value for Run 1









0.20; !- Value for Run 10

Material,

M07_Floor_insulation (80mm), !- Name

Rough, !- Roughness

=$e_floor_ins, !- Thickness {m}

0.038, !- Conductivity {W/m-K}

160, !- Density {kg/m3}

1000, !- Specific Heat {J/kg-K}

0.9, !- Thermal Absorptance

0, !- Solar Absorptance

0.6; !- Visible Absorptance

4

• Cork panel thickness:

For the cork panel thickness study in the rammed earth building, the following code has been added:

Parametric:FileNameSuffix,

Names, !- Name

E_cork_0.02, !- Suffix for File Name in Run 1









E_cork_0.20; !- Suffix for File Name in Run 10

Parametric:SetValueForRun,

$e_cork, !- Name










0.20; !- Value for Run 10

Material,

M07_Corkulation (80mm), !- Name

Rough, !- Roughness

=$e_cork, !- Thickness {m}

0.038, !- Conductivity {W/m-K}

160, !- Density {kg/m3}

1000, !- Specific Heat {J/kg-K}

0.9, !- Thermal Absorptance

0, !- Solar Absorptance

0.6; !- Visible Absorptance

TRITA TRITA-ITM-EX 2021:299

www.kth.se

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Evaluation of natural materials in Sustainable Buildings: A …1587579/... · 2021. 8. 25. · DB HE Documento Básico de Ahorro de Energía (CTE) DB HS Documento Básico de Salubridad