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The Applicability of the Bio-Climatic Facade in a Hot and Humid Climate Zone A Study of Geoffrey Bawa's Architectural Works

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The Applicability of the Bio-Climatic Facade in a Hot and Humid Climate Zone A Study of Geoffrey Bawa's Architectural Works
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    The Applicability of the Bio-Climatic Facade in a Hot and Humid Climate Zone  A Study of Geoffrey Bawa’s Architectural Works   MINGWEI SUN Department of Architecture and Built Environment, University of Nottingham,  Nottingham, UK, laxms10@nottingham.ac.uk BRIAN FORD Department of Architecture and Built Environment, University of Nottingham,  Nottingham, UK, Brian.Ford@nottingham.ac.uk BENSON LAU Department of Architecture and Built Environment, University of Nottingham,  Nottingham, UK, Benson.Lau@nottingham.ac.uk Achieving desirable comfort conditions in a place where the climate is hot and humid can be challenging. An increasing reliance on air-conditioning is the inconvenient truth of the building industry. This paper investigates the environmental performance of a number of buildings by Geoffrey Bawa. The first part of the paper reviews Bawa’s architectural works in a chronological order and studies his approach to facade design for controlling internal comfort conditions. The second part of the paper investigates the environmental performance of one of those bioclimatic facades, the ‘Monsoon Window’ , and explores its potential wider application in the hot and humid climate zone. A comparative study is presented that is to define the thermal performance of a testing model by using Monsoon Windows. In order to investigate the applicability of the facade with monsoon windows and whether it is able to achieve passive control for internal environment, dynamic computational studies were used to interrogate issues and provide convincing evidences. The limitation of the srcinal ‘Monsoon Window’ was identified through simulation with  parametric variations. The findings show that selective use of a well designed ‘Monsoon Window’ can enhance the indoor environment and substantially reduce the reliance on air conditioning in office buildings. Keywords: Bio-climatic facade, Hot and Humid region, Natural Ventilation   PLEA2013 - 29th Conference, Sustainable Architecture for a Renewable Future, Munich, Germany 10-12 September 2013 The Applicability of the Bio-Climatic Facade in a Hot and Humid Climate A Study of Geoffrey Bawa’s Architectural Works   MINGWEI SUN 1 , BRIAN FORD 2 , BENSON LAU 3 1to3 , Department of Architecture and Built Environment, University of Nottingham, Nottingham, UK  ABSTRACT: Achieving desirable comfort conditions in a place where the climate is hot and humid can be challenging. This paper investigates the environmental performance of a number of buildings by Geoffrey Bawa. The  first part of the paper reviews Bawa’s architectur  al works in a chronological order and studies his approach to  facade design for controlling internal comfort conditions., The second part of the paper investigates the environmental performance of the ‘Monsoon Window’ and explores its potential wider appli cation in the hot and humid climate zone. The limitation of the srcinal ‘Monsoon Window’ was identified through simulation with  parametric variations. The findings show that selective use of a well designed ‘Monsoon Window’ can enhance the indoor environment and substantially reduce the reliance on air conditioning in office buildings.  Keywords: Bio-climatic facade, Hot and Humid region, Monsoon Window, Natural Ventilation  INTRODUCTION Before sustainable architecture became an important issue, even before the energy crisis of the 1970s or the vogue for critical regionalism in architecture for the Asian context, Geoffrey Bawa (1919-2003) was developing a design approach which embraced these concepts. He learnt from and applied traditional techniques in his work, which were under-valued qualities in the discussion about architecture in the tropical Asian context. Banham suggested that the humid and tropical climate requires a ‘Selective’ approach to environmental design, employing structure not just to maintain desirable environmental conditions,  but to admit desirable conditions from outside [1]. The distinction between ‘selective’ and ‘exclusive’ modes has also been discussed by Hawkes [2]. A similar approach was adopted in Bawa’s design work, from low-rise residential buildings, such as Carmen Gunasekera House (1958), to high-rise non-domestic  buildings, such as the State Mortgage Bank (1978). In this study, five buildings have been selected to reveal the designer’s explor  ation of bioclimatic architecture under his own ‘Selective’ mode . THE BIOCLIMATIC FACADE A study of Bawa’s works reveals that even though they were functionally different, there was a common theme in the architectural language by which these buildings achieved their bioclimatic purposes. The five cases shown in this study were the most representative of this idea in Bawa’s work.  Figure 1: The evolution of Bawa’s bioclimatic  facade.     According to the typology of each case, they evolved in three stages representing the development of his ‘Breathing Wall’ concept (Fig 1).  Bawa appreciated the role of the breathing wall as an environmental filter: ‘avoiding direct solar penetration, admitting currents for air and indirect light, excluding heavy rain and beating wind, allowing visual and spatial contact between inside and outside, excluding unwanted noise and providing security from intruder’ [3]. This interpretation of the development of the ‘Breathing Wall’ concept in Bawa’s works is the author’s view. This evolution occurred by trial and error, and at the time did not have the benefit of evidence-based analysis. The question therefore r  emains of ‘How well did it work  ?’ The air  -flow study described below, which focuses on the facade of the State Mortgage Building, investigated the environmental performance of this unique design and explored its potential wider application for the building in the hot and humid climate zone. THE STATE MORTGAGE BANK The State Mortgage Building still can be regarded as a good example of a ‘sustainable’ building by today’s standard because it meets most of the critical parameters for a ‘low carbon’ office for this climate [4]. This section investigates the ‘Selective’ mode, implemented  by applyin g the ‘Monsoon Window’ facade as a response to site and microclimate. Climate of Colombo The psychrometric chart for Colombo, Sri Lanka (Fig 2) with an adaptive comfort zone overlay shows a very small diurnal and seasonal temperature range. There is 93% of the year that the dry-bulb temperature varies from 24°C to 38°C, and the majority of the time is outside the comfort zone.  Figure 2: Psychrometric chart showing boundary of natural ventilation as a cooling approach for Colombo, Sri Lanka (Source: Climate Consultant 4)  By following Givoni’s boundaries definition [5] of climatic conditions with respect to the impact on indoor thermal comfort from natural ventilation, for the majority of the year, natural ventilation could be adopted to provide comfortable internal conditions. Design Principles Ken Yeang has suggested: ‘[The State Mortgage Bank] is probably the best example of a bioclimatically responsive tall building to be found anywhere in the world’ [6]. On an irregular shaped site, Bawa firs tly created a building that can harness the prevailing wind  because of its orientation and form (Fig 3), although this also makes it vulnerable to solar gain. Secondly, the big open working area with service cores on the perimeter of the building ensured good daylight and cross ventilation. Lastly, the terrace roof and the stilt structure of the ground floor acted as buffer spaces to the building mass. In detail, the building envelope was mainly covered by the ‘Monsoon Window’ facade: A clearstory protected   by an overhang above, a central pivot window in the middle and a retracted window sill with a horizontal air intake below. The ventilation slot on the window sill is the key element of this façade, allowing unimpeded airflow into the building regardless of the operation of the window pane. This type of façade provides the air changes required on rainy days when the windows have to be closed.  Figure 3: Site plan and floor plan with prevailing wind The design of the vent opening achieved not only the  path for airflow during rainy days, but also revealed its status (open or closed) to the occupants. This may be compared with an example from CIBSE AM10 [7] showing a concealed damper in the site-built enclosure  beneath the louvers of sills of French windows. It  presents a similar air vent path to the monsoon window,  but with a negative outcome, as it resulted in heat loss in winter due to its unclear indication of control status. The monsoon window, by contrast, set the opening in the height of the windowsill revealing a visible operational    status, which was more evident to occupants (Fig 4). Furthermore, the detailed design of the ‘monsoon window’ facade was very carefully considered with regard to its function. For instance, the central pivot window was easy to operate and maintain; the overhung eave with vertical baffle provided shading, and the sloping upper surface and the gutter help to drain off rainwater. The fenced high vents and monsoon windows also guaranteed the feasibility of night-time ventilation without risk to security.  Figure 4: The ‘Monsoon Window’  facade. MONSOON WINDOW In order to underline the importance of experiencing a  building, Bawa once said: ‘A building can only be under  stood by moving around and through it…’ [8] Unfortunately, the srcinal design of the State Mortgage Bank was altered due to the change of the ownership for several times, hence the srcinal design was lost and the computer simulation was required to evaluate  performance. There have been many studies based on computer and physical model testing for State Mortgage Building. Robson and Tan reported on a holistic environmental review of this building [4] and Tan et al finished a convincing study dealing with the ventilation  performance of the monsoon window [9]. In this paper, the thermal performance of the ‘monsoon window’ facade has been studied, to provide a further assessment of this type of facade design. The simulation tool adopted here is TAS [10]. Model Setup The model was restricted to a ‘shoe -  box’ form to minimise the influences of other variables such as the irregular shape of the building or the position of service cores. The basic dimensions of this model were 14.4m deep, 3.6m high and 45m wide, which followed certain environmental principles to guarantee that the internal space can be lit and ventilated naturally. The model faced the prevailing wind direction of Colombo as for the State Mortgage Bank building (south-west). The terrace roof and stilt structure were also represented; additionally, the two main facades of this linear model were equipped with the ‘Monsoon Window’ façade which complies with the srcinal details including 1.2m overhangs, high vents, windows and monsoon window slots. Test Cases In order to characterise the thermal performance of the  building reflected in this model, three office spaces on different level were selected (Fig 6). The locations are: A. The first floor (from 3.6m) B. The fourth floor (from 14.4m) C. The seventh floor (from 25.2m) Four scenarios for simulation To understand how the facade design performs, the efficacy of each element on this facade needed to be defined. Four conditions were tested and they are: 1. All windows are open. 2.   Only high vents are open, main windows and monsoon windows are closed. 3.   Only monsoon windows are open, main windows and high vents are closed. 4.   monsoon windows and high vents are open, main windows are closed (Fig 5)  Figure 5: The test scenarios of ‘Monsoon Window’  facade   Result The model tested four scenarios using TAS software. The thermal performance in May (the hottest month) is selected here for the following interpretation.    Comparative analysis of the scenarios With the simulation from TAS, the thermal performance of three selected spaces in four conditions, with same internal heat gain, are represented. The results for May indicate: 1. Scenario 1 showed internal temperatures only 1-2 degrees above the external temperatures, and only 20% of the time were they above 32°C. Compared with the other scenarios, this scenario provides the best results, since it possessed the biggest opening areas for ventilation (Fig 6.1). 2. In the cases where only high vents or monsoon windows are open respectively, the issue of overheating appeared due to the limited   opening area for removing internal heat gains. Internal temperatures were above 33°C for more than 35-45% of the time (Fig 6.2 and Fig 6.3). 3. By opening high vents and monsoon windows, the thermal performance revealed the second-best outcome which decreased the overheating problem remarkably and 60% of the time was under 32°C (Fig 6.4). 4. In each scenario, the space on the higher level showed slightly better thermal performance.  Figure 6: The frequency of dry-bulb temperature in May of the  selected spaces in different cases.    Comparative analysis with literature Compared to the study from Tan et al, the results of this study largely support their findings regarding the ventilation effect of the ‘Monsoon Window’ facade. The outcomes showed that the main window is the primary source of ventilation and the high vent or monsoon windows was unable to supply thermal comfort individually. However, there was a difference between the two studies. Fig 7 showed that, in Tan’s et al study,  by only opening the monsoon window, the wind velocity in the tested space is better than the case that the high vents and the monsoon windows were both open, which was described by Tan et al as a type of ‘dilution’ [9]. It contradicted Fig 6.4 in which the related thermal result was the best after scenario 1. The reason for such difference is potentially derived from the different configuration of the model tested in the two studies. As can be seen from the acrylic model in the study by Tan et al, in order to get the explicit results, the ‘Monsoon Window’ facade had only been equipped on the windward side whereas the leeward side was a wall with high-level slots representing a separate office. However, in Bawa’s srcinal design, it was an open working area with similar facade design on the  perimeter. The study by Tan et al represented the high vents on the leeward side (which played the role of the outlet enhanced by buoyancy effect) but there were more advantages embedded in the srcinal design: Firstly, the coupled facade design also showed an advanced air flow mode when the windward and leeward had switched. Secondly, the reason that high vents had been valued by Bawa in his design was  because the opening on the higher level could help the upper structure to remove heat, which was very useful for the roof structure of low-rise buildings and also high-rise buildings with internal floors (Fig 8). These two reasons may explain why having high vents opened when the monsoon window was operating is important thermally. This is supported by the outcome shown in Fig6.4.  Figure 7: Result from study by Tan et al (Source: [9]) Fig 6.1 Fig 6.2    Fig 6.3   Fig 6.4  
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