Friday, October 19, 2012

The Establishment of 'Air House' Standard in Tropical Countries : Part 5

Case Studies Analysis

The Selection of the Case Studies

Three case studies have been selected, two of which are traditional Malay houses, and the other a social house from the People’s Housing Project Scheme (PHP 2000). The Malay houses selected are the house of Datuk Baginda Tan Mas Mohar and the house of Andak Endah. The houses are located in two different areas; the house of Datuk Baginda Tan Mas Mohar in the Negeri Sembilan state (southern region) and the house of Andak Endah in Perak state (northern region).

The house of Datuk Baginda Tan Mas Mohar, built in 1850, and the house of Andak Endah, built in 1920, have been chosen as typology houses and represent two different forms. The house of Datuk Baginda Tan Mas Mohar has a basic twelve column structure, while Andak Endah has an expanded twelve-column structure. Social housing in Malaysia has been standardized, so using the People’s Housing Project (PHP) as the third case study is quite reasonable.

Table 15 shows the total external wall area and its opening areas percentage. The Datuk Baginda Tan Mas Mohar house has 16.5% opening areas and the house of Andak Endah has 17.9% opening areas. Meanwhile, PHP 2000 has only 8.9% opening areas. The size and location of opening areas are two key factors that can allow air to enter the building sufficiently. The two cases of Malay houses have larger opening areas compared to PHP 2000.

Simulation’s Design Settings

The selection of the 6.4 version of the Integrated Environmental Solutions Software (also known as (IES ) is due to its suitability towards the aims of the study, which is to simulate air temperature, relative humidity and air flow rate. For natural ventilation, MacroFlo, integrated into the IES simulation, is used to simulate airflow driven by wind pressure and buoyancy forces through elements such as windows, doors and openings. The simulation of MacroFlo runs from within Apache, which also simulates the indoor air temperature and relative humidity based on the ASHRAE design weather database. Meanwhile, MicroFlo uses a Computational Fluid Dynamic (CFD) to measure fluid flow and heat transfer processes around building spaces, which include the effects of climate (IES, 2012).

In this study, the simulation’s location database is Kuala Lumpur/Subang weather with the latitude 30 12’ North and longitude 1010 55’ East. The sea level height is 8 metres with the mean dry-bulb temperature 36.4 0C and wet-bulb temperature 16.1 0C. No HVAC system is applied, while east-west orientation is used in all simulation models. The openings of all samples assigned as window/door side hung with opening angle is 900, and opening hours range from 08:00 am to 10:00 pm. All the external walls are categorized as exposed walls without any obstacles.

According to Saini (1970), air temperature, relative humidity and air movement are the elements of climate which affect the comfort and well-being of the people. These factors also have complex inter-relationships between them, and, to a degree, each affects the other. Therefore, in this study, these three elements will be measured in detail, as well as carbon emission and energy consumption.

Table 19 shows the building materials assigned to both Malay houses and PHP 2000 in IES. The right building materials are crucial to achieve accurate readings in simulation. However, several regional materials such as an attap roof (a thatched roof made from palm leaves), a bamboo thatched wall, and a gap-timber-floor are not available in the IES material database. Therefore, the closest materials shown in Table 19 were chosen.

Results and Findings

Indoor Air Temperature

Air temperature is the mean temperature of the air in the room (Mohammadi, et al., 2010). Based on Table 20, the mean air temperatures in the Malay house cases have lower results than PHP 2000 by a 1.7 0C margin. These results show that the large opening area at the perimeter walls and roof in Malay houses work well in promoting natural ventilation.

Moreover, the maximum air temperatures in PHP 2000 are lower than the Malay house cases by a 2.0 0C margin. These results show that the high thermal mass materials used in PHP 2000 have succeeded in reducing the internal temperatures of the house during the day. Meanwhile, the minimum air temperatures in the Malay house cases are lower than PHP 2000 by a 1.5 0C margin. It concludes that the lightweight materials used in a Malay house can release heat readily and cool the house at night.

Relative Humidity

Relative humidity is the water vapour pressure of the air expressed as a percentage of the saturation vapour pressure (Mohammadi, et al., 2010). According to Table 21, the mean relative humidity in PHP 2000 is lower than the Malay house cases by 5.9%. In addition, the maximum relative humidity in the Malay house cases is higher than PHP 2000 by 7.1%, and the minimum relative humidity in PHP 2000 is higher than the Malay houses by 4.3%.

Wolkoff and Kjaergaard (2007) suggest that the recommended level of indoor humidity in Malaysia should be in the range of 30% to 60%. Therefore, the relative humidity of the traditional Malay houses and PHP 2000 are not at the recommended level.

From the results, it can be deduced that the Malay houses have a high level of humidity and a low temperature, while PHP 2000 has the opposite. According to Saini (1970), as in physiological effects (body temperature and sweat production), the low temperature and high humidity conditions are the same as those with high temperature and low humidity. Therefore, the air temperature and relative humidity in both cases have less of an impact on thermal condition.

Internal and External Ventilation

MacroFlo external ventilation is the volume flow that enters through a MacroFlo opening, and MacroFlo internal ventilation is the volume flow leaving through a MacroFlo opening (Mohammadi, et al., 2010).

From the MacroFlo simulation’s results (Table 22 and Table 23), the traditional Malay houses recorded a higher internal and external airflow ventilation compared to both PHP 2000 units. The most significant value of external ventilation was recorded in the Andak Endah house with 1450.3 l/s (1.45m/s), compared to PHP 2000 with only 31.7 l/s (0.03m/s). The differences in terms of air movement in both Malay house cases are tremendous. The air movements leaving and entering the house are significantly higher than PHP 2000. Therefore, the maximum internal and external ventilation in the Malay houses achieved a better rate of wind speed of 1600.0 to 5400.0 l/s (1.6 to 5.4 m/s).

These findings are vital in this study because the movement of air, for instance, reduces the effects of humidity and air temperature (Saini, 1970). Therefore, a traditional Malay house that has high air movement is proven to have better thermal comfort than PHP 2000.

Carbon Emission and Energy Consumption

Thermal comfort theory is used as a guidance for the assembly of fabric and plants that will determine the environmental conditioning system (Fisk, 1981). Fish (1981) added that assembly can lead to many alternative uses for patterns and energy consumption. From the thermal comfort results discussed before, the high heat storage materials that contribute to high temperatures in PHP 2000 at night are one of the reasons air conditioning systems have been installed. This is the quickest way to reduce heat in the house but it also produces high-energy consumption and carbon emission.

Table 24 shows the comparison of carbon emission and energy consumption for two different PHP 2000s. One unit uses an air conditioning system, the other is fully naturally ventilated. Both carbon emission and energy consumption for the PHP 2000 with an air conditioning system are higher than the PHP 2000 that uses natural ventilation. The carbon emission and energy consumption for the air-conditioned house is 67% and 66% higher than the naturally-ventilated house. Even though an air conditioning system leads to an enormous increase in carbon emission and energy consumption, it is still the top choice for Malaysians in addressing thermal discomfort at home.

Summaries and Key Points

The selection of the case studies is based on house forms. The Andak Endah house has a basic form while the Tan Mas Mohar house has an expanded form. The location of the house that influences the stilt height is also one of the selection criteria. Therefore, these two houses are best served as typologies for their respective form group and location. Meanwhile, social housing has a typical standard design which can be constructed anywhere in this country. So, PHP 2000 is the right representative for social housing development in Malaysia.

From the simulation’s results, it can be deduced that the air temperatures in PHP 2000 and Malay houses show no significant difference within each other. The mean air temperatures obtained are within the comfort levels mentioned in part 4. However the relative humidity results are higher than their suggested level (part 4). Even though the relative humidity is high, there is only a small change in the air temperature. A change from 25 to 75% of relative humidity is predicted to move the temperature by only 1 0C (Fisk, 1981).

The crucial finding obtained from the simulation is the air movement. Air movement in this scenario is very important because it can encourage heat loss through the evaporation process. Low air movement does little to generate a body’s heat loss. Furthermore, Fisk (1981) suggested that air movement of about 150.0 l/s (0.15 m/s) or greater tends to increase air temperature and a body’s heat loss. In conclusion, a traditional Malay house that has high air ventilation movement in and out has the better shelter and can provide more comfort to the human body than PHP 2000.

On the other hand, the carbon emission and energy consumption for the naturally ventilated PHP 2000 are far lower than the PHP 2000 that uses an air conditioning system. The carbon emission and energy consumption levels for a naturally ventilated house are much lower than an air-conditioned house. The huge gaps here show that it is worth encouraging people to use natural ventilation methods rather than an air conditioning system. Malay houses, for instance, can best describe the concept of a naturally ventilated house. Therefore, some elements, such as the size of openings and their placement, can be forwarded to a detailed level.

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. 

No comments:

Post a Comment