Solar heat gain in residential buildings through roof

Abstract

As Sri Lanka is a tropical country, it is important to understand the science of solar heat transfer into buildings through roofs, walls and windows. Present study was aimed at studying solar heat transfer into residential buildings through roof. Study was carried out using a test cell of 8‟X8‟X8‟ in size with a selected roof design with four pitches. Surface temperatures of all four pitch surfaces and ceiling were measured every 5 minutes using Platinum resistant thermal sensors. In addition, attic, inside cell and ambient temperatures were recorded at the same time intervals. Direct solar insolation was measured using a pyranometer and for the measurement of indirect insolation, same instrument was covered using a strip of paper in order to obstruct direct component. Heat flux received by each pitch was calculated using Liu – Jordon formula. Heat flow from ambient to room was calculated using Sol – Air Temperature method. Throughout the study, it was assumed that heat entering through roof equals the heat passing through ceiling. Also this amount of heat is equal to the heat exchange between the room and surrounding. It was observed that heat gain through roof is dominant when compared with walls and window. Maximum room temperature was at a maximum few hours after noon. Also direction of roof inclination has significant effect on heat transfer. Assumption that was made equalizing heat flow through roof and entire roof structure is reasonable for this type of calculations.