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.
