A Comparative Study of Passive Design Features/Elements in Malaysia and Passive House Criteria in the Tropics

In the Tropical climate, buildings gain solar heat and penetration through the building envelope and glazing which can cause overheating and thermal discomfort of occupants. Therefore, a conventional solution is by using electro-mechanical cooling system in buildings which raises energy demands dramatically, leading to ecological loading. In order to mitigate the cooling load energy consumption, natural ventilation and heat avoidance techniques have been researched and applied in Malaysia. Passive building design is a method to protect dwellers from the influence of external thermal discomfort. Likewise, this is in line with the characteristics of Malaysian vernacular architecture. Yet, previous studies on passive building design strategies have not been compared to the Passive House principles. Therefore, this paper reviews, accumulates and compares studies on passive design features/elements in Malaysia and Passive House criteria in the Tropics. Through this study, it is verified that the Passive House principles are applicable in the Tropical climate and similarities and/or differences in terms of achieving thermal comfort and energy reduction between a Passive House and other buildings with passive design features and strategies were identified.


INTRODUCTION
Passive cooling components were developed and applied in vernacular houses in the tropical region over centuries to capitalise prevailing winds and orientation to the sun. However, its avoidance or inappropriate applications in contemporary house designs is an important issue that needs addressing (Nedhal Ahmed M. Tantasavasdi, Srebric, & Chen, 2001). La Roche (2001) pointed out that climate responsive building design is significant as it provides thermal comfort and energy savings for occupants thus, sustaining precious resources. Regrettably, new building designs' development do not consider local climatic conditions and the need for energy conservation as they are mostly developed to rapidly fulfil the really high housing demands. These have resulted in overall poor thermal performance of new buildings and the need for mechanical ventilation and air conditioning that lead to high rate of energy consumption (N.A.M. Al-Tamimi, Syed Fadzil, & Wan Harun, 2011). Therefore, this paper reviews studies on passive design features/elements and compares it with Passive House criteria in the tropical climate

RESEARCH METHOD
A library research of journal papers, conference papers and other documents relating to passive design strategies in tropical climates, thermal comfort and vernacular elements/features was conducted. All existing strategies/features were grouped into 12 categories according to their function. This helped the researcher in building a literature review, as well as a way to compare these aspects with Passive House principles. Searches on Passipedia which is an international Passive House database were conducted, reviewed and summarised in this study. Overall, this paper discusses a comparison of climate responsive features and Passive House criteria in the tropics.

REVIEW OF STUDIES ON PASSIVE DESIGN FEATURES/STRATEGIES
Thermal comfort is defined as ''…that condition of mind which expresses satisfaction with the thermal environment" (ASHRAE & ANSI, 2004). Thermal comfort has a significant implication on health, psychology and productivity of the working population who form the foundation of a country's economy (Latha, Darshana, & Venugopal, 2015). In tropical climates, buildings gain solar heat and penetration through building envelope and glazing. Hence, they become overheated during the day (Rajapaksha, Nagai, & Okumiya, 2003 As a means to achieve thermal comfort, passive design techniques can be applied in buildings. This is to avoid or limit solar heat gain, optimise natural ventilation, engaging prevailing winds and to provide adequate daylight (Mohd Zaki, Nawawi, & Ahmad, 2007). As the most important passive design element, the building envelope is a separator from the external environment and a protective layer from climatic factors influencing the building directly (Givoni, 1976). Hence, blocking off radiation of the sun, less heat absorption and transmission can lead to natural cooling in buildings (Ali, 2012). These techniques can also be termed as heat avoidance which can be applied to buildings to increase thermal comfort (Aflaki, Mahyuddin, Mahmoud Awad, & Baharum, 2015). There are eight key designs in order to prevent the building exposure to the sun in the tropics are as follows:

BUILDING ORIENTATION
Several studies have proved that the key to thermal comfort and energy-efficient building design is choosing the best orientation for the building (Al-Najem, 2002;Çakir, 2006;Manioğlu & Yılmaz, 2006;Syed Fadzil & Sia, 2004). Thomas & Garnham (2007) declared that building orientation should be specified in terms of solar angle and dominant wind direction. A proposed affordable housing design by Abdul Rahman, Md, Al-Obaidi, Ismail & Mui (2013) presented in Fig.2 shows that the living areas can be orientated East to West with a 10 meter frontage and 6.7 meter depth as opposed to the existing narrower frontage of conventional houses in line with a study by La Roche (2001). A study in Singapore also shows the best orientation of the building is East to West with longer building façades facing North and South to avoid harsh morning and afternoon sun (Wong & Li, 2007).

BUILDING FORM/SHAPE OF ARCHITECTURAL PLAN
According to previous studies, rectangular building plans with lengths facing North and South is best at avoiding solar radiation and heat gain from the East and West (Halwatura & Jayasinghe, 2007;Konya, 1980;Tombazis & Preuss, 2001). In addition, a study based on modified ASHRAE thermal sensation scale was carried out in Putrajaya and UTM campus showed that buildings which are close to each other can self-protect by shading their East and West facades from the direct solar radiation and thus have lower ambient temperature (Md Din et al., 2014)

SHADING
In the tropics, providing shading for both glass and opaque surfaces on the facades will significantly improve thermal comfort inside buildings (Latha et al., 2015). This can be done by having shading elements on the upper part of openings on the East and West facades (Aflaki et al., 2015), or having features such as verandas and lattice screens as in vernacular Mughal architecture which provides cooler internal spaces (Ali, 2012). Toe & Kubota (2015) recommended constant low roof eaves alongside the window top and strategically locating broadleaf trees which are taller than building height to shade the building. A solar penetration analysis on the KOMTAR building in Penang showed the depth of horizontal shading device design should be based on the appropriate sun path. Considering shading device orientation at this building, planning and calculation is also noted by Syed Fadzil & Sia (2004) to be of utmost significance if an energy efficiency awareness and environment friendly design is targeted.

MATERIALS/COLOURS
Internal thermal comfort is also influenced by the ambient temperature and humidity which are dependent upon specified building materials (Hyde, 2013). Latha et al. (2015) particularly identified certain materials such as vacuum insulation panel, phase change materials, aerated autoclaved concrete/autoclaved cellular concrete, polymer skin with good thermal properties are potentially suitable to be incorporated into various components of the building envelope to enhance thermal comfort. Façades with light colours or reflective paints were also proven to reduce building heat gain by reflecting solar radiation year-round for buildings located in warm and temperate climatic conditions (Costanzo, Evola, Gagliano, Marletta, & Nocera, 2013

WINDOW CHARACTERISTIC
The energy performance of a building depends on the building envelop especially the window (Hee et al., 2015). Research findings of Bülow-Hübe (2001) as discussed by Lee, Jung, Park, Lee & Yoon (2013) state that the window is responsible for 20-40% of wasted energy in a building. Even though the existence of window is to allow daylights into the buildings, having a minimum size for windows will limit heat gain or heat loss. N.A.M.  found that window position, optimum glass size and application of natural ventilation should be appropriately specified to mitigate solar radiation and heat gain indoors. Besides these, glass thermal and optical properties, window sizing and orientation are window characteristics that need to be considered (N.A.M. . Window glazing can improve the penetration system through its optical and thermal characteristics, such as thickness, coat, colour and gap filler between panes which determine the glazing thermal performance and daylight aspects. They generalised that thermal comfort can be enhanced by natural ventilation application and window to wall ratio (

VEGETATION SURROUNDING / INSIDE BUILDING
Vegetation surrounding building, as a traditional time-tested and proven method and a significant heat avoidance technique should be encouraged in tropical climates to provide shading for buildings, roofs and the surrounding areas as indirect evaporative cooling by vegetation shows a promising performance in improving thermal comfort within building shown in Fig.3 ( Aflaki et al., 2015;Latha et al., 2015). Toe and Kubota (2015) noted the vegetation and unpaved ground surface in the adjacent area of vernacular house when applied at a terraced house can mitigate ambient air temperature and moderate the amount of urban heat island intensity of the surrounding area especially during night-time. Another technique that affects the adjacent rooms' thermal performance is an internal courtyard (Sadafi, Salleh, Haw, & Jaafar, 2011).

INSULATION
Installing insulation in external walls is a significant heat avoidance technique. In order to achieve a low heat conductivity and a longer time duration, thick walls consisting of low thermal conductivity materials were proposed (Halwatura & Jayasinghe, 2007;Sadineni, Madala, & Boehm, 2011;Yıldız & Arsan, 2011). Another study by Abaza (2002) declared the importance of thermal insulation in conjunction with other building elements' impact on outdoor air flow to clarify the building thermal performance. Therefore, using thicker construction on external walls alongside East and West façades can prevent the larger solar heat gain (Wong & Li, 2007). Apart from the walls, Toe & Kubota (2015) stated that thermally insulated roof/ceiling can moderate the large solar heat gain due to the solar altitude at noon in the tropics and low-rise building form.

DAYLIGHTING
As Abdul Rahman et al. (2013) stated that by designing longer façade on the North-South side of the buildings, the dependence of artificial lighting will be mitigated. Mettanant & Chaiwiwatworakul (2014) also declared that natural daylighting via broad windows maintains the required indoor illuminance for buildings in the tropics and this can save energy from reduced usage of artificial lighting. Alternatively, Munaaim, Al-Obaidi,  considered fibre optic daylighting system as an innovative, sustainable, and green technology that provides interior lighting applied in tropical climates. However, it is shown that the fibre optic daylighting system has no significant effect in relative humidity even possibly increases the internal room temperature by 2C (M.A.C. Munaaim, Al-Obaidi, Ismail, & Abdul Rahman, 2015). During the review of several skylight roofing systems, these systems were found to be inappropriate for direct application in Malaysia

PASSIVE COOLING TECHNIQUES
Mohd Zaki et al. (2012) stated that passive cooling was an innovative architectural way of building design to attain climate responsiveness in the region, so that it maintains sustainable indoor thermal comfort conditions naturally. Cook (1989) clearly referred passive cooling to any architectural technique which prevents external heat, and simultaneously shifts indoor heat to natural heat sink. He categorised them into, five main methods of passive cooling which are radiative cooling, evaporative cooling, heat avoidance, earth coupling and ventilative cooling which are agreed by many recent studies by Aflaki et al.
Besides this, stack ventilation or vertical air flow is also useful as cool air is heated by human activities and the operation of home appliances/devices and this warm air escalates through the vertical architectural element/s and released from the building through openings at high level, as illustrated in Fig.5. Nonetheless, stack ventilation, essentially depends on the aperture height variations and also the difference between indoor and outdoor ambient temperature of the building. Sanusi, Shao & Ibrahim (2012) investigated passive ground cooling technology in hot and humid countries, where the ground can be used to absorb heat from the building in order to produce cooler indoor air. They found that the greatest temperature reduction was within the pipe buried at 1 meter depth underground. According to Labs & Cook (1989), in an earthcoupled building by sabotaging the building slabs' conduction and convection, the indoor spaces can be thermally unified with the subsoil. In moderate climates where the Earth temperature meets the comfort zone standard, this system is applicable (Aflaki et al., 2012).

ELEMENTS AND TECHNIQUES ON APPLICATION OF NATURAL VENTILATION
Natural ventilation as defined by N.A.M. Al-Tamimi (2011), is intended current of outdoor air through apertures that can mitigate the heat and remove relevant humidity by taking the wind and thermal pressure into account in the tropical climate. Latha et al. (2015) stated that the application of natural ventilation in buildings has become a phenomenon due to energy requirement, indoor air quality and environmental concerns associated with mechanically ventilated buildings. The usage of building space plays a major role in thermal comfort and the energy usage of the building. Aflaki, Mahyuddin, Mahmoud Awad et al. (2014) noted that the amount of air flow into the building is subject to the design of architectural features/elements. Their review of former researches shows that the most essential architectural features regarding natural ventilation are building orientation and layout, windows and apertures orientation and size among others. Besides these, various louver shapes and angles in openings, window-wall ratio (WWR) and window-floor ratio (WFR), openings' different forms for optimum pressure discrepancy are the most effective components and strategies on application of natural ventilation (Aflaki, Mahyuddin, Mahmoud Awad et al., 2014;Fung & Lee, 2015). Furthermore, air wells also allow stack effect process to take place and encourage air flow into the building so that existing indoor hot air will be exchanged with fresh and cool air. It works by taking in fresh air through openings in the building façade, discharging the warm air through the air well from the basement up to the roof level in buildings (Jafarian, Jaafarian, Haseli, & Taheri, 2010;Khanal & Lei, 2011). Alternatively, small-scale buildings can utilize chimneys and stack air ducts while large-scale buildings apply the atrium (larger air well) to pledge ample wind flow and velocity to achieve thermal comfort standards (Aflaki et al., 2012;Aflaki, Mahyuddin, Manteghi, & Baharum, 2014;Latha et al., 2015;Moosavi, Mahyuddin, Ab Ghafar, & Ismail, 2014). Double skin façade and double-skin roof are effective passive design strategies to curb heat gain into buildings by mitigating the reflective glass walls' conduction via protection (Aflaki et al., 2012;Allard & Ghiaus, 2012;Zingre, Wan, Wong, Toh, & Lee, 2015). Fig.7 Secondary roof system construction, source: Wong & Li (2007) In addition, to achieve natural ventilation at night time, proper location and accurate sizes of windows is needed. Replacing fixed-glass windows with operable or adjustable louvered windows, application of full-height windows or upper ventilating apertures to optimize its function in both ways can reduce cooling load in buildings (Aflaki, Mahyuddin, Manteghi et al., 2014;Schulze & Eicker, 2013). Studies by Kubota, Chyee &Ahmad (2009) andJamaludin, Hussein, Ariffin &Keumala (2014) in Malaysia showed that night-time ventilation is the best strategy to cool down buildings as compared to day-time and full-time ventilation. Building corridors can significantly direct and transfer air flow through some parts of buildings. Transferring the outdoor wind to indoor environment by corridors is another strategy to ensure maximum ventilation in building (Aflaki et al., 2012;Mohamed, Prasad, & Tahir, 2008). To invite more air flow into the building, narrow-width floor layout is more effective (Tombazis & Preuss, 2001). Furthermore, Aflaki, Mahyuddin, Manteghi et al. (2014) demonstrated that the speed of indoor wind velocity at a 13 th floor unit is higher than another unit on the 3 rd floor. It can be declared that building height affects the indoor air temperature and wind velocity directly.

PASSIVE HOUSE IN THE TROPICS
Passive House is defined by Passive House Institute (established in Germany) as providing thermal comfort in a building entirely by fresh air post-heating or post-cooling to achieve good indoor air quality requirement without the additional usage of recirculated air (Feist, 2007). Passive House standard in the tropical climate was determined by the Passive House Institute with a case study set in Singapore. Various aspects of Passive House standards in tropical climate were investigated including compactness (different ratios of exterior surface to enclosed volume from values typical for high-rise buildings to those typical for small single-family homes), insulation for wall, roof and floor, air infiltration through cracks and leakages, heat and humidity recovery from ventilation, glazing type, window area and orientation, absorption coefficient of exterior surfaces, and heat capacity. The tropical Passive House standard features include a sealed building envelope, average thermal insulation of 10-15 cm in thickness, reflective light colours on the building envelope with additional thermal insulation, windows with fixed shading elements, low-emissivity doubleglazed windows, and mechanical ventilation with energy recovery ("Passive Houses in tropical climates," 2014). Few of these principles, including interior insulation, although have been applied in cold climates, are applicable in the tropics ("Passive Houses in tropical climates," 2014). In order to optimize the energy efficiency and thermal comfort in the tropical regions, a cooling and dehumidification system should adopt sensible heat ratio to the respective requirements. Unnecessary energy consumption will be the result of utilizing a regular air-handling unit at an approximate air temperature of 15°C with an individual dehumidifier ("Passive Houses in tropical climates," 2014).

DISCUSSION
Prior studies have repetitively noted the importance of heat avoidance techniques and passive cooling in the tropical climate of Malaysia. Each can have a significant impact on energy reduction. This paper found that some passive features and strategies are applicable in certain buildings, for instance, solar chimney, stack air duct, double skin façade and double skin roof. Whereas, Passive House has a solid guideline that can be followed in order to mitigate energy consumption on cooling demand, while meeting the occupants' thermal comfort. Result from the comparison suggest that Passive House's principles can be applied in the tropics to render significant cooling load reduction. This is because the amount of solar radiation heat gain is reduced by wall and roof insulation and by double-glazed windows. Window shading that plays a great role in heat avoidance is also considered as a Passive House principle. Table 1 below presents the similarities and differences of both groups.