1 Seasonal Thermal Energy Storage (STES) for EDUCATORS (Academic Staff, Higher Education, Public Administration in Charge of Energy, etc) Miguel Ramirez

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Seasonal Thermal Energy Storage (STES)for EDUCATORS

(Academic Staff, Higher Education, Public Administration in Charge of Energy, etc)

Miguel RamirezDr Shane ColcloughProf Neil J Hewitt

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Contents

What is Seasonal Thermal Energy Storage (STES)?

Why use STES?

History of STES

How does it work?

Ways to store thermal energy

How much energy can be stored?

Where is it best used?

How much does it cost?

Case Studies

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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Storing cold during winter for use in summer

Storing heat during summer for use in winter

WHAT IS STES?

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

WHY STES?

Energy use of buildings accounts for 30-40% of the total energy consumption in the EU

60-70% of it is consumed for heating by the residential buildings

Heating demand for space heating occurs mostly in wintertime when solar availability is lower

Store solar thermal energy in summer for use in winter months

Northern European countries have average ambient temperature of approx. 5°C and annual solar irradiation up to 1000 kWh/year m² (Stockholm)

Data source: SoDa-is.com

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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Ancient PersiaIn 400 B.C 60 feet tall brick domes (Yakhchals) with wind catchers were used to store ice and keep cooling in ambient temperatures of 40°C

Romans1st Century A.D. used wells and transported snow to keep their food and wine cold on hot days

Cold HousesIn the 18th-19th century river water or ponds used to maintain low temperatures inside these structures for preserving food (Middleton, England – Glen River, Northern Ireland)

HISTORY OF STES – Storing Cold

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Gri

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Colc

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aw

esc

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Germany post WWIFirst feasibility studies started in 1920 due to the country limited resources.

USAThe Keck “glass” house in 1933 and MIT house in 1939 both made with glass and high thermal capacity materials for thermal energy storage

Denmark, SwedenDuring the 70’s oil crisis forced governments to look for alternatives. Small and large scale thermal storage systems were built combined with district heating systems

HISTORY OF STES – Storing Heat

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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HOW DOES IT WORK - COMPONENTS

Heat Source Solar Biomass Industrial waste heat..

Thermal Storage High thermal capacity Large volume Low thermal losses

Auxiliary & Distribution system Boiler, Heat pump District Heating network

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ParallelHeat pump, solar collector and STES work independently to meet heat demand

In SeriesSolar collector or STES act as a source for heat pump or in addition to other sources

Serial/ParallelThe heat pump or collector provides heat to the building, dependently or independently

HOW DOES IT WORK - CONFIGURATIONS

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ParallelThe solar collectors are connected directly with the storage tank and charge it with thermal energy during high solar radiation periods. The STES delivers hot water for domestic hot water (DHW) and the space heating system during the heating period (winter).When the temperature of the STES is lower than the required, the heat pump delivers the necessary heat to both the DHW and the space heating system. The heat pump thermal source is external and it can be either air, ground or from waste heat recovery.


Solar Collectors

STESHeat Pump (Air/Ground source)

DHW

LOAD

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SeriesThe solar field, STES tank and heat pump are connected in series. Heat is stored during high solar radiation periods. The solar collector can directly act as a source for a heat pump or directly via heat storage. The heat pump must be a water-to-water unit and it can satisfy the hot water demand from both the DHW and the buildings. The storage tank temperature can be maintained within a lower range of temperature according to the operation range of the heat pump’s source. By having a lower STES tank temperature, it reduces the thermal losses from STES.


Solar Collectors

STES

Heat Pump

DHW

LOAD

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Series/ParallelThe STES tank is charged by the solar collectors and provides heat to the DHW and buildings. When the temperature within the STES tank is below the minimum required by the load the heat pump starts operating. The heat pump extracts the remaining heat in the store to deliver DHW and space heating to the buildings. In all three cases the heat pump can operate during low electricity cost periods to heat the DHW tank in a cost-effective way. Moreover, an auxiliary system (i.e. gas boiler) must be used to cover the heating demand that cannot be covered by the STES system.


Solar Collectors

STESHeat Pump

DHW

LOAD

EXAMPLE OF THE SERIAL/PARALLELSTES OPERATION MODES(EINSTEIN PLANTS CASE)

ChargingThe charging of a STES system starts when thermal energy from the source (solar) is available. Solar thermal energy can be collected during summer months and stored to the STES tank for later usage. It is also possible to store and deliver thermal energy only when the tank has independent circuits for charging and discharging.

HOW DOES IT WORK – Serial/Parallel

Direct Discharging The discharging of a STES system starts with the heating season. The tank delivers heat directly to the buildings through a district heating or direct pipeline. The temperature of the hot water outlet is regulated according to the heating curve of the load. Maximum STES outlet temperatures are typically 80°C, (with pressurized tanks >100°C is possible).

TSTES > 50°C


Heat pump operation The heat pump operates when the STES output temperature is lower than the temperature needed by the load to fully cover the heating demand. Water from STES delivers heat to the evaporation cycle of the heat pump and the condensing cycle provides hot water with sufficient temperature to overcome the load needs.

10°C < TSTES < 50°C


Auxiliary system – BoilerWhen the temperature of the water in the tank drops (10°C) to a level which is out of the efficient operation of the heat pump, the auxiliary system starts. The thermal energy from the STES tank has been completely discharged and the load depends totally on the auxiliary system.

TSTES < 10°C


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Auxiliary system – Boiler/Heat Pump

An auxiliary heat source is essential to cover peak load and for periods when the storage tank is discharged

Heat pumps typically are three/four times more efficient than conventional heaters for the same amount of heat

Water-to-water heat pumps have a low return temperature to the source side. That temperature difference helps the stratification in the storage tank.

Lower temperature at the bottom of the storage tank causes higher collector efficiency and decreases thermal losses through the ground


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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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Latent Heat

Chemical Heat

Sensible Heat

WAYS TO STORE THERMAL ENERGY

Latent Heat StorageThe most common material used to store latent heat are solid-liquid Phase Change Materials (PCM). Thermal energy can be absorbed by the PCM in both solid and liquid states. However, they absorb large amounts of heat during the conversion from solid to liquid (melting temperature). PCMs can store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry or rock. When thermal energy is absorbed from the PCM storage, it changes from liquid to solid phase releasing its stored latent heat.


Thermochemical StorageChemical and sorptive heat storage systems (thermochemical), are promising technology approaches with considerable benefits compared to both the sensible and the latent-heat storage systems. Storage densities can theoretically be up to 10 times above those of the medium water, reducing thus the construction volume. Due to the nature of its process and the low temperature of the stored materials it can almost eliminate thermal losses. The combination of both advantages facilitates the efficient time-based storage of thermal energy and its transport.


Sensible Heat StorageSensible heat is the thermal energy transferred to or from a substance which results in a change of temperature. It is the most common and direct way to store heat, however the main draw-backs are the large quantities of material/volumes needed and the heat losses when the store medium is surrounded by lower temperatures. The use of water tanks for thermal storage is a well known technology. Innovative solutions can minimize heat losses by ensuring optimal water stratification and high efficiency thermal insulation.


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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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Q= m.cp.ΔΤ Q: Thermal energy stored m: Mass of substance used for storing heat cp: Specific heating capacity of storing

substance ΔT: Temperature change of storage medium

before and after charging it

HOW MUCH ENERGY CAN BE STORED

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Example:Solar collectors heat 100 m3 of water from 25 to 50°C, which is stored in an insulated storage tank. How much energy is stored in the water?

Q = m.cp.ΔΤ

m = ρ.V = 1000kg/m3 x100m3 = 100000kg

cp = 4.18 kJ/kg.K)

ΔΤ= 25°KQ= 100000 x 4.18 x 25 = 10450 MJ = 2.9 MWh


Kies/Wasser-Wärm espeicher

Erdsonden-W ärmespeicher

Heißwasser-W ärm espeicher

Som m er W inter

W ärm edäm m ungAbdichtungSchutzvlies

Kies/Wasser-Wärm espeicher


Heißwasser-W ärm espeicher

Som m er W inter

W ärm edäm mungAbdichtungSchutzvlies

Hot Water tank thermal energy store (HW) Pit Thermal Energy Store (PTES)

Borehole Thermal Energy Store (BTES) Aquifer-Thermal Energy Store (ATES)

~70 kWh/m³ 1) ~55 kWh/m³ 2)

15-30 kWh/m³ 30-40 kWh/m³1) Jmax=90 °C, Jmin=30 °C without heat pump 2) Jmax=80 °C, Jmin=10 °C gravel-water TES with heat pump

Kies/Wasser-Wärmespeicher


Heißwasser-W ärmespeicher

Som m er W inter

W ärm edäm m ungAbdichtungSchutzvlies


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STORAGE LOSSES

Losses from STES tanks can be high

A: conventional insulation material: λ = 0,05 W/(m·K), insulation thickness s = 0,2 m

B: conventional insulation material : λ = 0,05 W/(m·K), insulation thickness s = 2 m

C: Vacuum insulation: λ = 0,005 W/(m·K), insulation thickness s = 0,2 m

Time in days

Cooling down curve of a hot water store with a net volume of 10 m3 (cylindric shape: Ø 2 m, height 3,18 m). Start temperature 80 °C, ambient temperature 5 °C

Due to lower surface to volume ratios, large tanks cool down more slowly and are therefore favouredThis has led to a focus on STES in combination with District Heating

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

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WHERE IS IT BEST USED?

Building type Single House Multi Unit Development New Built (preferred) Existing buildings

Climate Conditions High annual solar

radiation & moderate heat demand in winter is ideal

Heating type District heating Low temperature

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STES ground conditions Geological structure Land space for Storage Hydrogeological characteristics (aquifers)

Thermal energy source Sufficient area for solar collectors (land, roof) Industrial thermal waste sources (temperature

range, distance to the heat demand point and availability)

District heating grid availability Type of use

Single load – (stable run) Independent dwelling usage (complex controlling

system)

WHERE IS IT BEST USED? - Considerations

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WHERE IS IT BEST USED? – EINSTEIN resources

Location within the EUSpace heating energy demand in the EU vary significantly from country to country. The main factors depend on the building stock, the construction period, building density and the local climatic conditions.

The best potential for STES system application in Europe are highlighted in the report: “Classification of EU building stock according to energy demand requirements.”

Residential energy demand vs. average ambient temperature. (ACC4: Bulgaria, Romania, Turkey, Croatia; EFTA3: Iceland, Norway and Switzerland; NMS 10: new ten member states since May 2004.

(Source: ECPHEATCOOL).

https://www.einstein-project.eu/fitxategiak/EINSTEIN-%20D1_1%20-%20update-150223.pdf





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STES integrationGiven the recent energy performance regulations in EU countries it is anticipated that buildings will have lower energy demand (<50kWh/m²yr). In that case it is possible to use lower supply temperatures for space heating systems thereby decreasing thermal losses. That makes STES systems better suited to the integration of low-energy heating systems. Integration of STES with a number of types of heat generation technologies, such as gas boilers, heat pumps, Combined Heat and Power (CHP) and distribution systems are discussed in this document: “Technology assessment HVAC and DHW systems in existing buildings throughout the EU”

http://www.einstein-project.eu/fitxategiak/EINSTEIN_D1_2.pdf

http://www.einstein-project.eu/fitxategiak/EINSTEIN_D1_2.pdf

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Design STES systems and EINSTEIN plantsNumerous steps need to be taken to design a STES system. They consist mostly of technical challenges and decisions such as dimension of storage tanks, location, solar field size and heating system retrofitting, need to be studied. Having a transient system which is influenced mostly by weather conditions, makes it possible to predict and determine the behaviour by stationary calculations. A comprehensive guide for planning and designing a STES system can be found here: “Design guidelines for STES systems in Europe”.For an overview of the design and installation of the EINSTEIN demonstration plants please click here.

https://www.einstein-project.eu/fitxategiak/EINSTEIN-D55%20v0.pdf

http://www.einstein-project.eu/fitxategiak/EINSTEIN%20DEL%207.1%20v1.pdf

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Decision Support ToolTo analyse the best approach for the preliminary design and CAPEX/OPEX of seasonal thermal energy storage systems in existing buildings, a Decision Support Tool (DST) has been developed as part of the EINSTEIN project. The DST helps users to identify the best suitable technologies and their performance according to specific conditions.

Climatic conditions Space requirements Equipment and integration requirements

(Solar collectors, STES, district heating, heat pumpand auxiliary system)

UsersCandidate users for the tool are Engineering and Construction companies with basic knowledge of HVAC systems who have no experience on STES system installation.For further information on the model please click here.

WHERE IS IT BEST USED? – STES Design Tool

http://www.einstein-project.eu/fitxategiak/EINSTEIN-D%202%201_def.pdf

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DST DescriptionThe Tool consists of three main parts:

Input data selection Calculations section Results section

Designing casesApart from a selection and evaluation tool of STES systems, the tool also allows users to analyse and compare different scenarios. Centralized systems as well as distributed configurations can be studied for each location and each level of heating demand for both existing or non existing buildings.

For access to the tool please click:DECISION SUPPORT

TOOL

WHERE IS IT BEST USED? – STES Design Tool

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WHERE IS IT BEST USED? – Combination of increased energy efficiency and use of renewables

Energy StrategyIn order for STES systems to be most effective, they need to be part of an overall energy strategy.This includes:

reducing the energy demand of the existing building by retrofitting energy efficiency measures

Integrating the use of renewables Integrating specialist solutions including STES

These decisions need to be optimised based on the variables applying for the specific case such as:

Climate Cost Building type

An Evaluation Tool has been developed to determineThe most cost effective combination of measures

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WHERE IS IT BEST USED? – Evaluation Tool

Configuration of the Evaluation tool

1.Definition of

study

building

• Selection of Climatic area • Selection of type of building• Surface of the building

2. Desired energy

reduction

• Select Range of savings

3. Calculat

e the

most cost effective solution

•Query to the database of results•- match with the optimal case (s) that meet the savings selected. •- identify the most cost effective combination of passive an active measures(including STES)

4. Results

• Best combination option selected• Primary energy savings. (-kWh/year)• Investment required (€)

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EVALUATION TOOL – The most Cost Effective Solution

Software Model for assessing the energy behavior of

existing buildings

Passive retrofitting strategiesSTES

contribution to cost

effectiveness

Evaluation Tool for most cost

effective frame work in

retrofitting

Decision tool for desgning and evaluation of

STES

MAIN GOAL“To develop a methodology evaluation tool for de most cost –effective global energy intervention framework for building retrofitting”

EVALUATION TOOL

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WHERE IS IT BEST USED? – Reference single family house

SFH: Single Family house

SFH 84,5 m2

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WHERE IS IT BEST USED? – Reference Multi family house

MFH: Multifamily house (block of flats)

0.00

2.00

4.00

6.00

8.00

10.0

0

12.0

0

14.0

0

16.0

0

18.0

0

20.0

0

22.0

0

24.0

0

0.00

50.00

100.00

DHW MFH

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MFH 676 m2

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WHERE IS IT BEST USED? – Sample outputs

0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.000 0.050 0.100 0.150 0.200 0.250 0.300

Ratio Total result per period/Primary energy consumed vs Primary energy

% Primary savings

€ s

avin

g/k

Wh c

onsum

ed

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%100%0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00Ratio Investment / Primary energy savings vs % Primary

energy reduction

best restults (Invest aproach)best results (20 y exploitation aproach)

% Primary savings

Curves of best ratios results (Pareto distribution)

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

HOW MUCH DOES IT COST?

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The costs and financial benefits of seasonal thermal energy storage vary widely.

Variables include: Size Climate (solar irradiation, outdoor temperature) Heating demand Type of STES District Heating integration Financial variables including inflation rate, fuel

inflation rate, internal rate of return, etc.

HOW MUCH DOES IT COST? – The STES tank

Examples of costs for STES tanksThere are different ways of analysing the financial performance of STES installations. The diagram shows the costs of a wide range of STES tank sizes used for large district heating systems. The cost of the investment decreases with size. The cost of the EINSTEIN STES tanks for both small and large scale scenarios is presented in the table.

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SiteSTES Size

{m3}Cost {€}

Cost/m3

{€}

Sweden

23 16225 705.4

Poland 800

Spain 180

Source: Solites

Passive House with solar DHW and space heating with STES

Quickest payback was for solar DHW and space heating system excl. STES (lowest cost option in year 16 & again in year 24 after refurbishment).

When the STES was added to the solar DHW & Space Heating system it represented the lowest cost option in year 33.

Note that the STES is required as an integral element of the system in order to avoid technical problems with stagnation.

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Source: Colclough & Griffiths, Applied Energy Journal 2016

HOW MUCH DOES IT COST? – Overall cost of heating

Example of a single dwelling STES installation

Costs presented include systems, operating costs and fuel and are adjusted for inflation and company discount factor (Net Present Value).

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Description Multiunit development

Number of units10 (4 commercial, 6

residential)

Total floor area {m2}381 plus 390 = 781

Total

Solar Array {m2} 50

Diurnal Store {m3} 3.3

STES Size {m3} 23

Space heating energy demand {kWh}

53,422

DHW energy demand {kWh}

7,417

Total NPV cost over 40 years {€}

405,415

Payback peiod {Years}

17

Saving compared with non Solar STES

27%

Building renovated to Passive House standard

Solar heating system with STES used

Payback achieved after 17 years


Example of a Small scale STES installation10 unit development with solar DHW and space heating with STES in Lysekil, Sweden

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The total cost of providing DHW and space heating is shown opposite. Costs include systems, operating costs and fuel and are adjusted for inflation and company discount factor (Net Present Value).

The costs of heating with District Heating (€514,492) exceeds that of using solar heating with STES with DH as backup (€405,415) over the 40 years considered

Full details of analysis available here (insert link to Del 7.5)


Example of a Small scale STES installation10 unit development with solar DHW and space heating with STES in Lysekil, Sweden

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Contents


Why use STES?

History of STES

How does it work?





Case Studies

Brennwert-KesselGas

H eizzentra leF lachkollektoren

W ärm enetz

So larne tzSaisona lerW ärm espeicher

W ärm eüber-gabestation

Central Heating

Plant

Solar Collectors

Seasonal Thermal Energy Store

Solar Network

Heat Distribution

Network

Heat Transfer Substation

CASE STUDIES

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STES Tanks under House 1st European 100% Solar House Oberburg, Switzerland In operation since January 1990

CASE STUDIES

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Oberburger Sonnenhaus First multi-family dwelling to be heated completely

with solar energy Oberburg, Switzerland 276m² of solar collectors 205m³ thermal storage tank

CASE STUDIES

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3.000 m² Flat plate coll. 4500 m³ Water tank

Hamburg (1996)

Friedrichshafen (1996)

Neckarsulm (1997) Steinfurt (1998)

Rostock (2000) Hannover (2000)

5.900 m² Flat plate coll. 63.300 m³ BTES

1.000 m² Solar-roof 20.000 m³ ATES

4.050 m² Flat plate coll. 12.000 m³ Water tank

510 m² Flat plate coll. 1.500 m³ Pit TES

(Gravel/Water)

1.350 m² Flat plate coll. 2.750 m³ Water Tank

Source: USTUTTCASE STUDIES

Chemnitz, 1. phase (2000)

Munich (2007)

Eggenstein (2008)

Attenkirchen (2002)

Crailsheim (2007)

540 m² Vacuum

tubes 8.000 m³ Pit TES

(Gravel/Water)

2.900 m² Flat plate coll. 5.700 m³ Water tank

1.600 m² Flat plate coll. 4.500 m³ Pit TES

(Gravel/Water)

800 m² Solar-Roof 9.850 m³ Water tank &

Boreholes

7.500 m² Flat plate coll. 37.500 m³ BTES

Source: USTUTTCASE STUDIES

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Seasonal Thermal Energy Storage (STES)for EDUCATORS

(Academic Staff, Higher Education, Public Administration in Charge of Energy, etc)

Miguel RamirezDr Shane ColcloughProf Neil J Hewitt

Documents

1 Seasonal Thermal Energy Storage (STES) for EDUCATORS (Academic Staff, Higher Education, Public Administration in Charge of Energy, etc) Miguel Ramirez