Radiative performance assessment of two roofs in Mediterranean and Equatorial climates

Abstract

In regions where the roof surface is the most exposed to solar radiation, the reduction of the heat flux transmitted through this element has a great impact on the cooling demand of buildings. Studying the possibilities of reducing cooling loads can highly influence the environmental and carbon footprint of the building stock worldwide. Although the main strategy to prevent solar access would be implementing shading systems, another approach could be taking advantage of the radiative cooling effect of the roof itself. Its efficiency depends on the roof properties (color, mass, thermal transmittance, etc) and on climate conditions (radiation, wind, humidity, etc). This paper deals with a comparative assessment of the radiative performance of two roofs exposed to different amounts of solar radiation depending on their percentage of cloudiness, and the repercussions over its surface temperature. Its aims is to evaluate the effect of radiative cooling depending on the local climates. Temperatures of two similar roofs, in Terrassa 41°33´LN (Spain) and in Santa Rosa 3°27´LS (Ecuador), were measured. Their transmittance, optical and thermal mass properties were considered in the calculations. The results obtained indicate that the effect of using the sky as a heat sink has a higher impact on the roof located in Terrassa (Spain) than the one in Santa Rosa (Ecuador). The results support that this behavior responds to the influence of the high presence of cloudiness on equatorial climates, which reduces significantly the heat losses in long wave radiation. The heat mass storage capacity of the roof could hinder even more the radiative cooling effect of the roof.