Thermal analysis of roof-spray cooling

Roof-spray cooling systems have been developed and implemented to reduce th e heat gain through roofs so that conventional cooling systems can be reduc ed in size or eliminated. Currently, roof-spray systems are achieving great er effectiveness due to the availability of direct digital controls (DDC). The objective of this paper is to develop a mathematical model for the heat transfer though a roof spray cooled roof that predicts heat transfer based on existing weather data and roof heat transfer characteristics as describ ed by the transfer function method (TFM). The predicted results of this mod el are compared to the results of existing experimental data from previousl y conducted roof-spray cooling experiments. The mathematical model is based on energy balances at the exterior and interior surfaces of the roof const ruction that include evaporative, convective, radiative, and conductive hea t transfer mechanisms. The transfer function method is used to relate the e nergy balances at the two surfaces that differ in amplitude and phase due t o the thermal resistance and thermal capacitance characteristics of the roo f. The model is shown to yield relatively good predictions of heat transfer rates through the roof. The calculation method shows promise as a relative ly simple means of predicting heat gains based on calculation procedures th at are similar to those frequently used by practicing engineers. (C) 1998 J ohn Wiley & Sons, Ltd.