Abstract:
This study investigates the effects of roof colour, slope, material and insulation on the indoor temperature of a hypothetical single-story building under Malaysian weather condition. The results would fill the gap of information on some aspects of passive cooling in Malaysia. The roof elements were combined in various configurations to represent different properties. The values for each configuration were used as inputs, together with Malaysian meteorological data, in a series of simulations using the software IES-VE. The various configurations were assessed and ranked based on their impact on the minimum, average and maximum operative temperatures (OTs) as well as % of hours of discomfort (%HD) of the building interior. The results for the whole set of 360 roof configurations showed OTs that were high compared to 29°C for thermal comfort. Roofs with lower solar absorption (SA) showed lower OTs and %HD compared to those with higher SA. Steep roofs produced lower minimum and average OTs and %HD than gentler slopes. The roof without insulation showed lower minimum OT and %HD (at night), but higher maximum OTs (during the day), compared with roof with insulation. The role of Aluminium foil in cooling the inside space is more noticeable for SA 0.8.
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All top 20 performing roof configurations involved SA 0.2 and consisted predominantly of gypsum ceiling, 60° roof slope, metal and composite material, and surface emissivity 0.9. These configurations are suitable for buildings that are occupied predominantly at night, with no or little active cooling systems. Buildings for daytime occupants would require more extensive cooling for thermal comfort. The conclusion is that passive cooling can be achieved with the following roof elements: (a) roof materials with low SA, or high SA with Aluminum foil, (b) high roof slopes with larger roof surface area to increase the heat dissipation especially at night through radiative cooling, and (c) ceiling with moderate insulating properties to help balance the day and night temperatures. Utilizing these optimal roof elements allow buildings to minimize solar gain during the day and increase heat dissipation at night which in turn decrease the demand for cooling.
