ENERGY STRATEGIES IN THE TROPICAL CONTEXT THE USE OF SIMULATION TOOLS IN INFORMING URBAN BIOCLIMATIC DESIGN IN A MALAYSIAN HIGHRISE DEVELOPMENT

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1 The 2005 World Sustainable Building Conference, ENERGY STRATEGIES IN THE TROPICAL CONTEXT THE USE OF SIMULATION TOOLS IN INFORMING URBAN BIOCLIMATIC DESIGN IN A MALAYSIAN HIGHRISE DEVELOPMENT Puteri Shireen Jahnkassim PhD 1 Abdul Razak Sapian PhD 2 Maisarah Ali PhD 1 1 Department of Building Technology and Engineering, Kulliyyah of Architecture and Environmental Design, International Islamic University Malaysia, Malaysia. puterishr@iiu.edu.my; maisarah@iiu.edu.my 2 Department of Architecture, Kulliyyah of Architecture and Environmental Design, International Islamic University Malaysia, Malaysia. arazaks@iiu.edu.my Keywords: bioclimatic design, high-rise, simulation tools, computer fluid dynamics, tropical. Summary Current growth in the urban context in Malaysia has seen an increase in high-rise housing particularly condominiums with adjacent public plazas. The drive for energy efficiency has increased the need to utilize daylight and natural ventilation as opposed to air conditioning as much as possible, in the public areas of these large-scale developments. The paper presents the results of an environmental performance analysis of a mixed development project which demonstrates the use of simulation tools in informing strategic design decisions in energy-conscious design. Naturally ventilated areas such as covered plazas and walkways and features such as sun-shading are analysed with the aim to provide an appropriate level of bioclimatic envelope under the Malaysian climate while acceptable comfort conditions. Urban forms are considered as three-dimensional structures that can be manipulated and enhanced to achieve better environmental performance and indoor conditions in tropical conditions. Simulation tools such as computational fluid dynamics (CFD) are used to assess the implications of design options and suggest improvements. The tools are used to gain insight into wind conditions and temperature distribution in semi-opened spaces and link findings to issues of thermal comfort in the tropics. From a range of vertical and horizontal profiles of wind, temperature and pressure distribution in the plaza and high-rises i.e. selected levels i.e. near ground level, at mid- level and at upper levels - improvements are tested to further enhance comfort and alleviate discomfort. The plaza are studied in terms of the three stacked thermal zones where air movement and thermal stratification are studied and design options tested. This include also air movement in the podium areas and walkways of apartments which can assist in improving ventilation and air change rate in internal spaces and voids in order to save energy while not sacrificing user comfort in the tropics. 1. Introduction Currently in the urban context in Malaysia, there is a rise of high-rise developments particular high-rise apartments and condominium with adjacent pedestrian spaces some of it which supports commercial activities such as outdoor bazaars and food-courts. The recent trend in covered plaza areas which function like external atriums - can be seen in various new developments. These act as commercial hubs where small businesses can run regardless of the weather in the tropics. Glass canopies are used as they admit daylight and can produce a bright atmosphere to enhance goods and services. Because such common spaces are an increasingly popular in large commercial buildings in tropical countries, it is therefore important to ensure that they do not commit to a lifetime of high energy consumption. Under tropical conditions - particularly with glazed structures - there are various problems due to high heat gains. The performance of a covered atria which admits daylight will also admit solar gain at the critical times of the day. These problems can be linked the following two natural phenomena in hot climates: Greenhouse effect: Short wave radiation from the sun passes through glazing to warm interior surfaces and spaces. The re-radiated heat in the form of long wave radiation is not able to pass back through the glass

2 Stack effect: The stack effect is the result of convection within an open space. The warmer, less dense, more buoyant air rises to the top of the space, and tries to exit. This results in a positive pressure at the top of space and a negative pressure at the bottom. If the air cannot exit, then this results in the stratification of air by temperature especially apparent in a tall closed volume. Under these conditions, external parameters such as outdoor temperatures, wind speed and solar radiation has to be filtered in order to improve comfort conditions while at the same time, saving energy. One of the focus of investigation is the wind penetration into internal spaces such as internal light-wells, walkways, gaps between buildings and covered plaza while another focus is to assess the comfort implications of a series of what if options with respect to building form and features under tropical conditions. In the past, bioclimatic issues are not given enough consideration in the practice of urban design largely due to the lack of appropriate tools. However predictive tools have gained usage and can assess the impact of urban structures based on the urban microclimate i.e. such as sun and wind factors. Hence the aim is to show how environmental techniques can be applied to energy-conscious urban design - while at the same time to demonstrate that sustainable design require a continuous collaboration within the various specializations in the design team. Thus the objectives of this study can be summarised as: 1. To analyse the impact of selected building elements in urban forms such as canopy and voids in high rises and plazas in terms of temperatures and air movement in the semi-outdoor environments. 2. To analyse the impact of selected built elements in terms of the thermal comfort of occupants. 3. To suggest improvements to the urban bioclimatic form in terms of design based on the simulation and visualization output. 4. To further analyse the incremental impact of these improvements. 2. Methodology The case study is a mixed-development project in a suburban area of Kuala Lumpur, Malaysia - which consists of a 21 (6D1 tower) and 26 ( 6D3 tower) storey high-rise apartment and two rows of units threestorey shop houses with a 2200 m 2 covered plaza. The sensitivity of various design parameters to the impact of climate are tested particularly in terms of wind and sunlight environment and concentration of these environmental forces in and around the buildings. This provides a platform for the applications of Computational Fluid dynamics (CFD) techniques and visualization where the environment around, within and over the urban forms are visualized - complex - including surface pressure distributions. In terms of wind analysis as well as thermal comfort, the computational fluid dynamics tool i.e. MICROFLO and zonal analysis tool MACROFLO provide the overall method of investigation. The simulations runs were done for the month of June which represent the hottest times of the year the parameters analysed include room air distribution, pressure regime analysis, and analysis of temperature profiles internally and externally. Successive simulation runs are undertaken and results in terms of occupant comfort, indoor temperature, vertical and horizontal distribution of airflow are studied. 2.1 Criteria for assessment The criteria for assessment in terms of neutral temperatures is partly based Abdul Shukor s (1993) study on thermal sensation and thermal comfort votes for Malaysians has found that the Malaysian neutral temperature was 28.3 C (based on 50% relative humidity). The thermal comfort interval of Malaysians was found to be 25 C to 31.4 C at 50% relative humidity. Wind levels on comfort is based on these where a level below 0.5 is considered as still air and uncomfortable while levels between 1.5 m/s and 2.0 m/s is considered as thermally acceptable. Overall, the criteria for the overall assessment are based on: The use of appropriate climatic strategies through filtering strategy of minimizing the negative impact from the surrounding climate while maximizing its positive impact; The use of strategies that are in line with the climatic approach; Achieving the above while maintaining an acceptable level of occupant thermal comfort. 2.2 The Plaza description and environmental study The 2005 World Sustainable Building Conference, The Plaza represents a covered court within the complex that has been designed for public use. The sunhken areas contain vegetation and landscaping termed as eco-cells. They provi de not only the visual and functional focus for the complex, but acts as a thermal modifier - creating a micro-climatic oasis within the complex. The glazed canopy designed for daylight admission - will cause elevation the internal air

3 MODEL IT 3D Model Creation MACROflo Simulation Boundary Boundary conditions conditions MICROflo Simulation Internal CFD External CFD Figure 1 Plaza and high-rise apartment model for simulation (shown here with 6D3 tower only) - the triangular plaza with glazed canopy and arms of plaza and surrounding shop houses. Figure 2 Simulation process showing the link between MACROFLO ( thermal analysis) and MICROFLO ( CFD) analysis and input data temperature within the plaza and large vertical temperature gradients. The initial proposal for overhead louvers acting as external shading could not proceed due to cost constraints. Therefore mechanical ventilation i.e. extract fans were designed to remove the excess heat. This causes upward displacement system due to the natural driving forces of stack and wind effects and enhance the air movement through inducing an updraft through the vertical cross section of the plaza Thermal stratification analysis (CFD Micro-flow) To predict the temperature stratification inside the plaza, the latter was split into four stacked thermal zones i.e. three floors and the roof zone. The degree pf mixing of the outside air with interior air in the lower parts of the atrium is a critical factor in determining the overall thermal comfort. The following assumptions were considered in the simulation: All interior adjoining spaces were held at constant temperature. The exhaust system of the plaza was considered in establishing the air flow pattern of the plaza space Wind analysis walkways and common areas Following the dominant winds for the location of Petaling Jaya Malaysia, the dominant winds are from North, South and Northwest. Based on the meteorological data, the CFD studies were undertaken for three sets of wind direction incident on the high-rise towers; Parallel. Perpendicular. Oblique (45 o ). Two models were drawn representing the two towers using Model-IT. Assumptions for the external CFD simulation are as follows: Parameter Table 1 Assumptions in CFD (MICROFLO) analysis Assumption Average wind flow 1.32 m/s ( average for 23 years i.e )* Wind exposure Suburb The 6D1 tower consists of apartments with public facilities such as swimming pool, gymnasium etc located at Level 4 i.e. at the podium level. The aim is to gain insight into wind conditions at these spaces i.e. the vertical profile of wind distribution and horizontal profile at three selected levels i.e. near ground level, at midlevel and at upper level. Th ree wind directions (0 o (parallel), 45 o (oblique) and 90 o (perpendicular) i.e. at right angles to both buildings) are tested.

4 3. RESULTS AND DISCUSSION 3.1 PLAZA CONCOURSE AREA The vertical temperature profile display the effect of thermal stratification with an average of up to 4 o C of temperature difference between the floor and the apex of the plaza. The MACROFLO zonal tool is used to analyse the impact of infiltration and natural ventilation on temperature gradients and thermal comfort.the tool uses a zonal air-flow model to calculate bulk air movement in and through the building, driven by wind and buoyancy induced pressures. Overall, the conditions in the plaza closely resemble a typical naturallyventilated space in the tropical context. The results (Fig. 4) are fed to into internal CFD analysis for further visualization output. As seen from Figure 5 to 11, with the correct improvements, comfort conditions inside the plaza will remain at an acceptable level of 28 C 31 C even without the exhaust fan operating. Exhaust fans further helped to remove excessive heat by aiding the driving natural forces of stack and wind effect. It should be noted in terms of strategy, the reduction of the heat gain into the plaza during the day should be balanced with the need to quickly release heat to the cool air outside at night that accumulate from interior mass, people and lights. Comfort conditions in the enclosed plaza greatly depend on the extent to which solar heat gain can be minimized and excess heat removed i.e. through the following strategies: 1. The use of selective glazing on the glass canopy at the roof level will greatly enhance the performance of the canopy. 2. The provision of heightened openings at the apex of the plaza. These allow removal of excess heat by cross ventilation which is trapped on the upper parts of the plaza. It is predicted that the wind-generated suction at the inlet above the roof level can be increased by increasing the height of the glass canopy above the exhaust fans. More plants and landscaping can be placed at the arms of the plaza particularly on the western arm can also help since it reduces heat gain through wind movement. An example of the impact on the temperature at body level across the plaza can be seen in Figure 3. Temperature (C) :00 06:00 12:00 18:00 00:00 Date: Mon 12/Jun Air temperature: eco (de le te.aps) Dry-bulb temperature: (de le te.aps) Air temperature: plaza (de le te.aps) Figure 3 Temperature variations at body level at plaza concourse and eco-cell location without extractor-fan

5 Figure 4 PLAZA (internal CFD - section through concourse and eco-cell) Vertical distributions of variations in air velocity at 2 pm- acceleration of airflow can be observed at arms of plaza 3.2. HIGHRISE APARTMENTS - RESULTS (EXTERNAL CFD) The walkway represents an open air space and hence the internal conditions closely follow the external conditions. Under such conditions, improving comfort depends on higher indoor air speeds. The flow of outdoor air through a building extends the upper limit of the comfort zone beyond the limit for still air conditions and this provide a direct physiological cooling effect. The most noticeable findings are that in general when the winds are parallel to the 6D1 tower, the central walkway is efficiently cross-ventilated, compared to the 90 deg and 45 deg wind directions. At an average of 1.32 m/s, wind speeds at 1.55 and 1.73 m/s can be experienced within the walkways at lower levels. Winds at higher speeds can be experienced at higher levels. The wind speed increases as one moves from one level to another Comfort Zone Figure 5 External winds on 6D1 tower (external CFD) - Northerly winds effect on 6D1 in general at 1.36m/sec

6 Comfort Zone Figure 6 Cross section through podium and apartments showing scooping of northerly winds from below into the voids in walkways - vertical distribution through voids shows wind speed up at 0.8 to 1.54m/s Upper wind scoop Podium scoop Enhanced analysis model Profiled canopy Figure 7 Several of enhanced features to improve ventilation of voids in tower 6D1

7 Velocity pick up Still air = 5 levels Velocity pick up Half-way climb Figure 8 Section through 6D1 high-rise apartment (external CFD analysis) showing impact of northerly winds ( with Y deflector or scoop) Figure 9 Section showing northerly winds impact (with alternative profile of the wind scoop) -ve pressure Figure 10 General outlook of the effect of Southerly winds on 6D1 tower with the enhanced features ( vertical wind distribution - initial value at 1.36m/sec) Figure 11 General outlook of pressure contours due to the impact of northern winds with an alternative wind-scoop feature 4.0. CONCLUSIONS AND FURTHER STUDIES The study describes a case study within which a variety of simulation tools were integrated in the architectural design process to minimize the expenditure of energy while providing acceptable thermal comfort under the tropical climate. A number of strategies were developed to exploit natural energy of daylight and winds under the tropics. Recommendations include the use of sun-shading in the apartment units on critical orientations (east and west), a heightened ventilation stack in the plaza to further induce an

8 up-draft of air to 'cool the plaza and wind-scoop features to induce a higher air change rate in internal voids of the high-rises. Under naturally-ventilated conditions, comfort conditions for users and occupants can be enhanced through both passive - i.e. enhancement of certain design features and mechanical means. Basically under the Malaysian conditions, comfort is difficult to achieve - particular in the daytime under semi-external conditions this requires higher airspeeds through inducing cross ventilation and enhanced air change rate while reducing solar gain and heat gain from all potential sources. The overall goal is to achieve acceptable comfort conditions to users without incurring high energy expenditure throughout the year. In terms of performance of the plaza, the results show that comfort conditions depends on : 1. The extent to which solar heat gain can be minimized and excess heat removed; 2. The enhancement of air movement within the concourse area and reducing heat gain from potential external sources. The internal walkways in the high-rise apartment represent naturally ventilated areas which contain all mechanically-ventilated spaces in the apartments such as toilets and kitchens. Voids were integrated into the design to increase air change rate i.e. reduce the potential accumulation of heat, humidity and odors in these areas A higher level of airflow can significantly aid in the constant removal of heat and odor while at the same time introducing continuous fresh air to the occupants. In the tropics, the effectiveness of natural ventilation strategies however has to be balanced with the need to protect the spaces from heavy rain. It was found that air flow through the current proposed podium layout can be enhanced through minimizing obstruction in the walkways. The use of a wind scoop from the bottom and top of the towers can further catch and enhance the wind according to prevailing directions. Results of the vertical wind distribution through voids in the high-rises show that with selected features, airflow can be enhanced by the scooping of wind particularly from certain directions throughout the year.. Further studies are necessary to determine the level of obstruction in the walkways and impact on airflow and areas of still air or wind shadows in the voids. The innovative features such as wind scoop above the towers represent both aesthetic and environmentally features that will be the focus of further research and investigation. It is anticipated that through the completion of the building, involving the installation of the canopy, and a wind capture mechanism in the tower, these features should provide an platform for field investigations to further validate the simulation results and further develop such features as part of energy-conscious design under the Malaysian climate References FANGER, P. O Thermal comfort Analysis and Applications in Environmental Engineering, London : Mcgraw Hill Book Company. GIVONI, BARUCH, Climatic considerations in Building and Urban design : Van Nostrand Reinhold. ABDUL SHUKOR, A., Human Thermal Comfort in a tropical climate. PhD thesis, London: University of London. LIM, BILL, Natural ventilation and air movement in tropical highrise buildings, Environmental Design Criteria of tall buildings, Lehigh University, Bethlehem: Pennsylvania USA; POTVIN, ANDRE, Assessing the microclimate of urban transitional spaces, Proceedings of Architecture, City and Environment, Proceedings of PLEA 2000, Cambridge, UK July 2000 pp ; STEEMERS, KOEN AND RATTI, CARLO, Informing Urban Bioclimatic Design. in Proceedings of the 17th EAAE International Conference, The Teaching of Architecture as a multi-disclipinary practice University of Plymouth 1999; LAM, K.P., WONG, N.H. AND CHANDRA, S., The use of multiple Building performance simulation tools during the design process a case study in Singapore, Proceedings of the Seventh International IBPSA Conference, Rio de Janeiro, Brazil, August 13-15, SAPIAN A.R., MADROS, N.H., AND AHMAD, M.H. (2002). Computer Simulation: An Alternative Method in Studying Natural Ventilation at High-Rise Building Due to Urban Wind Condition. Integrated Energy Building Design Seminar. Organized by Centre for Education, Universiti Teknologi Malaysia. JAHNKASSIM, P.S., IP, KENNETH, "Environmental and architectural impacts of bioclimatic highrises in a tropical climate" ; Proceedings of the Sustainable Building 2000 International conference October 2000, Maastricht, Netherlands.