Monday, October 22, 2012

The Establishment of 'Air House' Standard in Tropical Countries : Part 8

The Establishment of ‘Air House’ Standard in Malaysia

From Passivhaus to ‘Air House’

In Europe, Passivhaus (Passive House) standard has been established to achieve the most suitable thermal comfort condition in a building during winter and summer. According to Audenaert, et al. (2008), ‘passive house is a type of low-energy building; design is oriented to make maximum exploitation of passive technologies, assuring a comfortable indoor climate during summer and winter without needing any conventional heating or cooling system’. The passive house concept focuses on airtight insulation that can prevent air infiltration and retain heat in the building. Its aim is to achieve 10 times less heat energy than the same standard designed building (Feist, et al., 2005). Table 33 shows the Passivhaus standard that has to be achieved in order to claim Passivhaus certification in the United Kingdom.

Table 34 shows the common construction criteria for Passivhaus standard, which involves a high level of insulation on the walls, floors and roofs; a continuous air tightness layer on the window frames; high thermal mass materials and thermal bridge-free construction; and a mechanical ventilation system with a high efficiency heat recovery. The Passivhaus standard can help to reduce 80% of carbon reductions as a legislative target for the UK Government (Passivhaus Trust, 2012).

Inspired by the Passivhaus concept, there is a need for a design standard to be established in Malaysia (or perhaps in the tropical region) for designing a building that can achieve a balanced thermal comfort by using natural resources such as solar and wind without dependence on mechanical equipment.

In a tropical country, air temperature, relative humidity and air movement are all vital factors in achieving a good level of comfort. With high temperatures day and night, and high humidity throughout the year, a building design that can channel the heat out is very important. Air movement through large opening areas is the key element in achieving thermal comfort in Malaysia.

The air movement is suggested to be between 0.15 to 5.4 m/s, which can be defined as a standard. Moreover, low thermal mass materials (lightweight) are the best option for this kind of climate condition as they do not retain heat and release it readily. The house that has met this standard could be called ‘Air House’.

Initial Concept of ‘Air House’

In order to reduce carbon emission and energy consumption of a building, especially in social housing, the use of natural resources such as solar radiation and wind is particularly valuable. A wise use of natural resources has been adopted in the design of a Malay house with balanced temperatures day and night, preferable humidity and large volumes of air movement in and out.

Thus, the theoretical model that has been developed and tested has achieved the Air House standard equivalent to a traditional Malay house. This Air House standard produces cross ventilation by allowing a suitable amount of air movement inside the building through some percentage of external opening area. This standard should be defined, and the thermal comfort results from the Malay houses and TM cases in Tables 35, 36, 37, 38 and 39 are the most suitable and valid parameters to be used as the Air House standard.

The main findings from the results are:

• The mean air temperature in Malay houses and TM ranges from 25.2 0C to 27.2 0C (Table 35). This range can be considered the best air temperature in a naturally ventilated building in Malaysia.

• The minimum relative humidity in Malay houses and TM ranges from 30% to 60% (Table 36). This range is achievable and therefore can be considered the preferred humidity range in a naturally ventilated building.

• The mean internal ventilation in Malay houses and TM cases (except the dapur and serambi) ranges from 0.15 to 0.4 m/s (150.0 to 400.0 l/s) (Table 37). Meanwhile, the external ventilation in Malay houses and TM (except the dapur) ranges from 0.30 to 1.45 m/s (300.0 to 1450.0 l/s) (Table 38). Thus, the preferred range of air ventilation in a naturally ventilated building is 0.30 to 1.50 m/s.

• The external opening area in a Malay house is 15% to 20% (table 39), while in TM, the opening areas on the walls facing outside (open space) is 25% and the wall facing inside (corridor) is about 50%. These percentages could be the best configuration of opening percentage in a naturally ventilated building.

• The best carbon emission for a naturally ventilated building is 2571 kgC02/year, and the energy consumption should not be more than 5.1963 MWh/year.

The findings listed above are the initial parameters than can be used as the first Air House standard in Malaysia.

‘Air House’ Standard for Naturally Ventilated Building in Malaysia

Based on all the results defined in Malay houses and theoretical models, the proposed Air House design standard is listed in Table 40. The air temperature ranges from 250C to 270C. The relative humidity for ‘Air House’ is 30% to 60%. Meanwhile, the air movement is between 0.30 to 1.50 m/s. The total energy consumption for Air House standard is less than 5.0 MWh/year and less than 2500 kgC02/year for carbon emission.

Table 41 shows the design parameters for a naturally ventilated building in Malaysia. 15% to 25% of an opening area is recommended for an external wall that faces an open space, while for a wall covered by shade or facing another block, 25% to 50% of an opening area is recommended. As higher altitude provides higher velocity, the units located on the eleventh floor and above should have a smaller opening area than units on the first to tenth floors. Furthermore, to promote air movement and cross ventilation, the four components of opening in Air House that should be implemented are bottom louvers, windows, top louvers and high louvers. The proportionate rule of these openings is 2x : 2x : 1x : 1x relatively, as shown in Figure 65.

Moreover, the unit plan layout should be in proportion of 1.5x for walls parallel to the corridor, and 1x for walls perpendicular to the corridor (Figure 65). To provide shade from sun radiation and rainfall, the minimum overhang recommended is 0.6 metres, while to promote better air circulation around the building, breaks between units are recommended. In terms of material selection, Air House standard uses prefabricated, lightweight and low thermal mass materials for the walls, floor and roof components.

Researched and written by Mohd Firrdhaus Mohd Sahabuddin; co-founder of 'Air House' and this article was a part of his dissertation which titled 'Traditional Values and Their Adaptation in Social Housing Design: Towards A New Typology and Establishment of ‘Air House’ Standard in Malaysia' for MSc. Advanced Sustainable Design in The University of Edinburgh. Copyright 2012. 

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