Effectiveness of passive cooling strategies of indoor thermal conditions for terrace house under hot and humid climate

Abstract

Global warming has caused the air temperature to increase and this has a serious impact on the urban area whereby causing heat wave during the summer in temperate climate area and all year long in tropical region. In Malaysia, heat wave has caused residential buildings especially terrace houses in urban areas to experience thermal discomfort. Passive cooling strategies such as natural ventilation and building retrofit method is proven to be a more effective method to resolve thermal discomfort. Therefore, the objective of this study is to assess the performance of passive cooling with different natural ventilation and building retrofit methods on improving the indoor thermal conditions for terrace house in hot and humid climate conditions. The performance of each method was assessed based on the estimated operative temperature (Top) in the building and compared with American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE) Standard 55, European Standard EN15251, and adaptive thermal comfort equation (ACE) developed from ASHRAE RP-884 database for hot and humid climate. The field measurement to measure the thermal conditions of the house was conducted in two stages in a corner terrace house located in Kuala Lumpur, Malaysia. Climatic data that influenced the Top, such as outdoor and indoor air temperature, relative humidity, outdoor wind velocity, indoor air velocity, indoor globe temperature, and outdoor solar radiation were measured. In the first stage, four types of natural ventilation which were full day ventilation (FV), full day no ventilation (WV), day ventilation (DV), and night ventilation (NV) were adopted to evaluate the performance of different natural ventilation strategies. The measurement was conducted in all rooms on the first floor. In the latter stage, the measurement was carried out in the master bedroom located on the first floor due to its west facing orientation and it being the hottest part in the investigated house. A study of four approaches on natural ventilation combined with different building retrofit methods which are high density polyethylene (HDPE) nets as roof cover, heat insulation above ceiling, and active cooling method with ceiling fan were conducted to analyse how each combination of methods assist in the thermal performance of the room. The results from the first stage showed that the mean indoor temperature under natural ventilation was approximately 27–37 °C, and FV and DV recorded better correlation between outdoor and indoor temperature compared with WV and NV. Although natural ventilation could improve the thermal condition in the room, but it was still not enough to achieve the acceptable indoor thermal condition under relevant international standards. The use of roof cover in the second stage reduced convective heat flux of approximately 70–80% in the attic and 88% in the room. Meanwhile, the mean of daytime air temperature in the room was reduced approximately 1°C. However, the heat insulation layer above the ceiling did not contribute much in improving thermal condition of the room during daytime. Whereas the thermal condition in the room became worse during night time due to the heat trapped by this heat insulation layer. As a conclusion, a roof cover with HDPE nets managed to improve the compliance on ACE hot and humid climate from 38% with only natural ventilation to 48% after a roof cover was added on the roof. Due to the effectiveness of improving the thermal condition in the house, this passive cooling method employing a roof cover with HDPE nets has the potential for further research and to be developed as a passive building retrofit method for low-cost landed houses with roof tiles in Southeast Asia such as in Indonesia and Thailand.