With high economic growth and rapid urbanization like many Southeast Asian countries, energy consumption in cities had raised tremendously in Malaysia as much as fivefold as stated in the National Energy Balance 2003 Malaysia published by the Ministry of Energy, Water and Communication. Due to our year long hot and humid tropical climate, total number of households with air conditioners has grown dramatically from 13,000 in 1970 to 775,000 in 2000 as household incomes increased. Thus, passive cooling techniques (without the use of air conditioner and fan) are important to be developed in order to decrease energy usage for indoor environment cooling purpose. According to several studies conducted in temperate climate, night ventilation, a passive cooling technique which can be done through opening the windows at night to allow cool outdoor air to reduce the indoor air temperature and also the temperature of building structures, especially in concrete buildings. This cooling effect continues till the next day, lowering and delaying the highest indoor air temperature achieved.
Since the effectiveness of night ventilation on the building thermal comfort depends on both climate condition and type of buildings, it is important to examine this passive cooling technique in tropical climate too as there are not many studies done. This study conducted in Johor Bahru for 6 days tested the effectiveness of night ventilation in terraced houses of Malaysia by comparing the effects of night ventilation (open windows at night) with daytime ventilation (open windows during the day), no ventilation (close windows at all time) and full-day ventilation (open windows at all time) in 3 respective cases. No fan and air conditioner were used in this study. Many Malaysians tend to open the windows during the day and close the windows with air conditioner running throughout the night. Thus this study can show whether a change of window-opening behavior can lead to a better thermal comfort during both day and night.
When windows were open during the day for daytime ventilation, the indoor air temperature is similar to the outdoor air temperature as outdoor hot air entered the building. As a result, the heat was stored in the building structure and slowly released during the night when the windows were closed, causing a higher indoor air temperature compared to outdoor outdoor. This high indoor air temperature during night time could lead to the current excessive use of air conditioners to cool down the building. On the other hand, nighttime ventilation allowed the building to cool down at night, and the cool air was maintained during the day with closed windows. The overall indoor air temperature was lower for the building with nighttime ventilation during both daytime and nighttime. When there was no ventilation, outdoor air did not enter the building all day and night, leading to a slightly high indoor air temperature compared to building with night ventilation. In average, the indoor air temperature was slightly higher than outdoor air temperature. When the windows were open all day and night for full ventilation, the result showed that the indoor air temperature was still higher than night ventilated room. During the day, the indoor air temperature was similar to the outdoor like the daytime ventilated building. Even though the building was allowed to cool down at night like the nighttime ventilated building, the building was already heated up during the day, causing the building to cool down slower.
As conclusion, night ventilation technique would be effective in reducing indoor air temperature during fair weather days for Malaysian terraced houses. However, this technique might not be suitable for rainy days due to inconsistent heat radiation from the sun and outdoor air temperature. Thus, opening the windows during nighttime can help maintaining a relatively comfortable indoor air temperature without the usage fan and air conditioner, leading to a lower energy consumption in order to keep the indoor environment cool.
Source: Kubota, T., Toe, D. H. C. & Ahmad, S. (2009). The effects of night ventilation technique on indoor thermal environment for residential buildings in hot-humid climate of Malaysia. Energy and Buildings, 41: 829 – 839
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