Classification of Natural Ventilation Strategies in Optimizing Energy Consumption in Malaysian Office Buildings

Procedia Engineering 20 (2011) 363 – 371

1877-7058 © 2011 Published by Elsevier Ltd.doi:10.1016/j.proeng.2011.11.178

Available online at www.sciencedirect.com

Procedia

Engineering Procedia Engineering 00 (2011) 000–000

www.elsevier.com/locate/procedia

____________ * Corresponding author. Tel: +6-06-758 7888; fax: 6-06-758 7599. E-mail address: [email protected]

The 2nd International Building Control Conference 2011

Classification of Natural Ventilation Strategies in Optimizing Energy Consumption in Malaysian Office

Buildings C. C. Siewa*, A.I.Che-Anib, N. M. Tawilb, N. A. G. Abdullahb, M. Mohd-Tahirb

aSchool of Quantity Surveying and Construction Management, Legenda Education Group, BUTL Batu 12, Mantin 71700, Malaysia bDepartment of Architecure, Faculty of Engineering & Built Environment,Universiti Kebangsaan Malaysia (UKM), Bangi 43600 ,

Malaysia

Abstract

Buildings have been defined as one of the major contributors to environmental problems in construction and operation stages. Intensive researches have been conducted to intensify green building designs by using alternative sustainable construction technologies and operation approaches in order to reduce energy use, and at the same time, to maximize the utility of natural resources. One of the strategies that are widely applied in the building operation recently is to optimize the potential usage of natural ventilation within an interior building space. This paper explores literally the conceptual approaches of classifying physical passive designs to optimize the application of natural ventilation within building zones. Through these findings, the categories of physical designs can be classified in five major groups, which are Air Wells, Façade Designs, Ventilation Openings, Corridors and Shadings, and Blockage and Partitions. © 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Universiti Teknologi MARA Perak and Institution of Surveyor Malaysia (ISM).

Keywords: Natural ventilation; Physical Passive Designs; Multiple Regression Analysis

1. Introduction

The construction sector intensifies the utility of resources, especially the energy consumption during the occupation stages. It is found that buildings consume about 40% of total world energy [1]. Among the distribution of energy usage in a building, ventilation and air-conditioning contribute to the highest percentage, especially in office buildings [2],[3].

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Generally, office buildings consume more energy if compared to other building types. The utility of

energy in office buildings is within the range of 100 to 1000 kWh per m2, depending on the location of the buildings, building dimensions, and the number and types of equipment used in the office buildings. For instance, in the United States of America, the average energy use intensity has achieved 300 kWh per m2, and there is about 79% contributes to lighting and ventilation alone. In United Kingdom, 72% of the total energy is used for these two elements. Besides that, the consumption of energy used is expected to grow tremendously within the coming 15 years, from 1,200 Mm2 to 2200 Mm2, an increase by 50% [4].

In the local context, in order to successfully overcome this issue, alternative energy sources have to be utilized [1], and thus, a number of green buildings have been built since 1990s. These include Mesiniaga Office Building was completed in 1992, Securities Commission Building in 1999, Menara Telekom Office Building in 2001, Low Energy Office Building in 2004, Pusat Tenaga Malaysia in 2007, and more recently, Diamond Building in 2010. Besides that, there are a number of new constructions which emphasize the issue of saving energy still in their design, planning and construction stages. According to GBI’s categories of green buildings, these are not only limited to office buildings, but also for commercial buildings and residential buildings for both existing and new construction [5].

Although most of the strategies applied in such buildings are more oriented either to promote the use of renewable and clean energy, or to reduce the energy usage. This indirectly provides the researchers a good opportunity to explore and study the effectiveness and efficiency of such innovative construction and building operation methods that have been applied so far.

Therefore, it can be concluded that if the application of natural ventilation in office buildings is feasible, it is not only helping the owners to reduce energy usage, but also decreasing the ventilation operation costs significantly [6], [7], [1]. However, how effective are these physical passive designs in order to achieve the targeted aim. How many types of natural ventilation can be classified these are two major questions that the researcher look forward to answer in this research.

2. Natural Ventilation Operation in Buildings

Basically, air movement is the main component in the overall ventilation process, and it is quite necessary to be considered in the process of integrating the building forms, openings and building orientation [8]. The data to be collected under air movement includes air velocity, temperature, relative humidity and pollutant air flow pattern. These data are important to determine, evaluate and simulate the thermal comfort and the indoor air quality that can be provided by the building under study or in the planning and design stage [9]. However, the conditions of outdoor air movement will also influence the performance of indoor air movement by the difference of air pressure applied onto a building facade through by relevant passive designs and openings [10], [11].

Generally, the natural ventilation in buildings can be summarized into two types, which consists of air pressure ventilation or known as wind force, and stack effect ventilation or thermal force [12].

Air pressure ventilation can be summarized as the horizontal air movement where the air flows into the building due to the differences of air pressure between the outdoor and indoor environment. The cool air will flow through the window and door openings or the building claddings into the rooms, as the air temperature indoor is much warmer. The patterns of air flow through openings can be classified into

365C.C. Siew et al. / Procedia Engineering 20 (2011) 363 – 371C. C. Siew, A.I.Che-Ani, N. M. Tawil, N. A. G. Abdullah, M. Mohd-Tahir/ Procedia Engineering 00 (2011) 000–000

single sided ventilation (where the air flow in and out at the same openings on the same facade), and cross or double side ventilation (where the air flow in and out at different openings on different facades).

However, stack effect ventilation is the condition of vertical air movement when the cool air has been warmed up by human activities and operations of indoor machinery, and the warm air move vertically and is discharged out from the buildings through chimney and air well.

These concepts of ventilation operation are shown in the passive design elements in the conventional non-air conditioned buildings before the green buildings are constructed in Malaysia. Such figures can be found in most of the traditional Malay houses [13] and some shop houses in the cities and towns.

3. Strategies of Natural Ventilation

Passive-based ventilation systems are implemented in traditional buildings long before the air-conditioning system comes into place. Yet, some of the elements can still be found and widely applied in the existing and new construction. For certain green buildings, the principles of design and operation of these passive designs are absorbed into their construction practices. Overall, the elements that ensure sufficient air changes and ventilation rates in buildings can be classified into two major categories.

3.1. Physical elements

The elements classified under these categories are the construction components that are physically observed, measured, analyzed and evaluated objectively. The elements classified under this category are the elements which play the functions of converting the direction of air flow or wind blow into or out from particular regions or zone of a building. These include: 3.1.1 Air well design This design strategy helps to circulate the air flow vertically to replace the used hot air with cool fresh air through the stack effect process. Air well design or also known as an air tower or wind catcher in some arid region is one of the most ancient passive designs that existed in the human construction history [14]. It ventilates by taking in the fresh air through the openings on the building facades, and discharging the polluted air or warm air through the vertical duct or opening in the buildings from the basement up to the roof level. Through this stack effect, the polluted indoor air can be filtered and disposed effectively and efficiently, especially during the day time [15], [16]. However, the ventilation design faces a few limitations in application. These limitations include: the possibilities of insect and dirt from outdoor, uncontrollable air flow and limited use in areas where the air velocity is low [17]. Chimneys and stack air duct are the alternatives of small sized ventilation structure to serve specific building zones.

Besides that, for larger air well or known as atrium, it plays a part in providing stack effect ventilation within a building space. As taller the buildings are, the space of atrium will be increased to ensure that there is sufficient space for air circulation. However, atrium design needs to suit the local air flow conditions, and thus, the effectiveness of its application is quiet limited [18]. Passive cooling effect can further be enhanced by adding man-made fountain or evaporative cooling systems to provide cooled air stream into the buildings [12].

3.1.2 Façade design


Building façade also plays the function of introducing the outdoor fresh air into the building zones by creating ‘rough’ surfaces in order to create the turbulent effects. The building façade consists of roof, walls and other openings, such as doors and windows. These components play the functions of controlling the air inflow and outflow, and they provide one of the alternatives to ensure the indoor environment can be maintained through the mixing of indoor air with fresh outdoor air. The optimum façade design can therefore reduce the cooling load significantly, and further, minimize the size of mechanical components [19]. These include double skin façade designs which reduce the transmission of heat into the building through the protection of reflective glass wall and air barrier [12], [20].

Wing walls are the alternative façade design solutions to direct the external air flow into the

building by projecting portions of the walls perpendicularly from the windows. However, these need to depend on the local wind direction, air velocity and the aesthetic values preferred by the owners. 3.1.3 Ventilation openings

Ventilation Openings play a major function by directing the entry of fresh air (when the openings are designed as windward) and discharging the used air (when the openings are designed as leeward) through the effects of air pressure difference between indoor and outdoor areas. The success rate of ventilation implementation in a building is also determined by the number of openings of windows, doors and other elements on the building façade, and these elements should be planned and designed properly during the design phase [18]. Window openings can be considered as one of the main components to control the access of both daylight and ventilation and help to save artificial daylight and ventilation [21].

Besides the openings sizes, the placement and orientation of the windows will also determine the

distribution pattern of air flow within a building zone [22], [14]. Vents and louvers are other openings for natural ventilation of which the location depends onto the indoor activities and also the architectural designs’ requirements [14].

Basically, single side ventilation openings can reduce the cooling requirement by 30%, whereas

the night ventilation can achieve the same result as the single sided day time ventilation. If these two ventilation designs are applied at the same building zone, the total reduction of cooling requirement will reach the target at about 40% [23]. 3.1.4 Corridors and shading

Generally, building corridors and balcony help to channel and deliver the air flow to the required building zones. These elements can be described as the connectors between the open space outdoor and isolated internal building spaces. According to Mohamed et al (2008) [24], the efforts to integrate the application of corridors in buildings is one of the strategies to design a building in response to the local climate. This means that corridors can play the function of transferring the air from outdoor and channelling it into the required building zones. However, the effectiveness of these passive elements will be limited due to the strength of air flow and the draught levels. If the buildings are ventilated by air-conditioning system, this will cause the air-leakage and heat transfer from the gaps of openings. Thus, this will reduce the effectiveness of the HVAC operation and consumes more energy for operation.

However, these shortcomings can be minimized by providing more green space around the

corridors and isolate the corridors from the polluting sources. For the corridors that surround the building facades, they will provide an air pressure zone for outdoor air to transfer into the indoor environment, through detailed design and integration with other passive elements, the level of air pressure amplification


can be achieved, and thus, the requirement of air change per hour within particular building zone can be realized.

The optimization of ventilation to cool down the indoor environment of an office building can also be enhanced through the process of reducing the absorption of external heat, such as solar heat, into the building. These include the installation of thermal insulation materials in the walls, tinted glasses and passive solar shading elements [12],[25],[26]. 3.1.5 Blockage and partitions

Besides all the positive design parameters that amplify the process of air flow circulation in buildings, the parameters that reduce the effectiveness of airflow may also need to be considered, such as partitions and walls [27], [28]. However, these elements are needed due to basic requirement of human activities, such as privacy and storage. Therefore, an optimum proportion is designed to achieve a balanced for both ventilation effectiveness and space utility efficiency. The categories of the physical passive designs can be illustrated as shown in Figure 1.

Figure 1. Categories of Physical Passive Natural Ventilation Design Components

3.2 Non-physical elements

Besides physical elements which impose direct impacts onto the air flow distribution, non-physical elements include the policies, cultures of practices and even habits and strategies applied also play a part to minimize the energy usage while the suitable indoor comfort is maintained during the time of occupation. These include: 3.2.1 Night ventilation

Night ventilation can improve the cooling effect of the indoor environment by delaying the time to switch on the air-conditioning system and using less energy to cool down the office spaces at night due to less heat loss and higher ventilation rate[12].

Building Facade

Ventilation Opening

Air Well Corridor &

Shading

Blockage &

Partitions


3.2.2 Adjustments made by occupants

This is provided that the occupants are free to adjust themselves, including the types of clothes, and the environment, such as opening a window or switching on a fan, to maintain their comfort level. Thus, the actual comfortable thermal level actually varies from person to person.

4. Effects on Outdoor Spaces onto Natural Ventilation Performance in Buildings

The effect of outdoor spaces should not be excluded in this study as the performance of natural ventilation in building zones is very much depended on onto the characteristics of the surrounding site environment. The factors of wind direction, topography and open areas may affect the volume of air circulation the building spaces. Thus, these give impacts onto the physical design of the building, such as follows:

4.1. Building Orientation

Integration of building orientation with natural ventilation is a challenging task as the designers needs to study the impact of the wind pattern, wind directions and building exposure areas in order to obtain the most optimum ventilation effects [6]. Details of site feasibility study needs to be carried out to ensure the strategy of cooling can be implemented [29], [17]. Certain standards have been suggested to optimize the ventilation effect due to building orientation. For instance, Anselm (2006) [29] further suggested that the optimum ratio between the length and width of an office building in hot and humid climate zone should be 1:1.7, and the building should orient to north or south to avoid exposure to the major opening to the sunlight.

4.2. Building Shape

The building shape influences the effectiveness of ventilation from the perspective of height, stack effect and issues regarding to the air velocity and air flow directions. The effectiveness of ventilation can be further improved by upgrading some advances in openings design onto the building façade [17]. Besides that, the existence of the nearby buildings and their impacts onto the building itself will also affect the air pressure onto the buildings, and hence, further improve the ventilation performance [23].

5. Model of Analysis

The model used to analyze the implication of thermal comfort implication between the passive ventilation design and the overall enclosure of building space for both the conventional non-air conditioned buildings and the new green buildings is based on Multiple Regression Analysis, which operates in Excel format.

According to Allison [30], this model framework is very useful to analyse the relationship of influence of the parameters onto a particular scope of studies, and the coefficient of each parameter are applicable to indicate the predicted value for the output simulated. Thus, it is quite useful for the researchers and designers when they need to optimize or test the feasibility of their ventilation design during the planning


stage in the future. The results evaluated and predicted are more reliable as the model is developed based on the local site characteristics and actual feedback from the building participants.

6. Expected Findings

Based on the concept of the research, there are two major stages to be applied in order to operate this research model to achieve the best design option for the occupants:

6.1 Stage One:

The respondents are requested to provide feedback onto the HVAC usage level of the building zones that they occupy. A list of scales is given for evaluation: scale 1 is for the lowest rating, up to 9 which is the highest.

6.2 Stage Two:

Under this stage, the percentage of coverage of each passive design element studied is measured, studied, co-related and evaluated with the overall building zone façade. The inputs of each passive design element will be treated as the regressor in the multiple regression formula, and thus, the final output of the most optimum passive design proportion of particular building design can be identified.

Hence, through the integration of these two major stages, the final output of the main indicator can be identified based on the multiple regression analysis process onto the regressors. The feasibility value of the particular design will be determined in co-relation with the proportion of passive design elements of overall building facades. Based on this model approach, a number of alternative building designs can be testified and a final building design can then be justified as the most optimum ventilation design to maximize both the application of natural ventilation and the thermal comfort levels. For situations which cannot meet both these requirements, mechanical ventilation may be necessary. The illustration of the model can be simplified as shown in figure 2.

Physical Components

123456789

Enclosed Buillding Zone under studied

HVAC Usage

Ranking

Averaged Value

Multi Regression Analysis

Air Well

Façade Design

Ventilation Openings

Corridors & Shading

Blockage & Partitions

Non-physical Design Figure 2. Operation Procedure of Multi Regression Analysis for Natural Ventilation Components


7. Conclusion

Therefore, it is clear that the main function of this multi regression analysis model is to evaluate the effect of passive designs of natural ventilation onto the energy usage for maintaining particular comfort level within a particular building zone. With the integration of these parameters in the overall design of a building, the most optimum ventilation design can be identified, and thus, the effectiveness and efficiency of each passive design elements studied can be further evaluated. Through this process, the particular percentage score in the design layout will be the blue print or major reference for the designers, especially for passive ventilation designs, in future. References

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Classification of Natural Ventilation Strategies in Optimizing Energy Consumption in Malaysian Office Buildings