An Improved Technique for Computing the Top Heat Loss Factor of a Flat-Plate Collector With a Single Glazing

Abstract

A different approach to evaluate the top heat loss factor of a flat plate solar collector with a single glass cover is proposed. The equation for the heat loss factor in the analytical form is employed instead of the semi-empirical form hitherto employed for solar collectors. The glass cover temperature is, however, estimated by an empirical relation. (This relation replaces the empirical relation for the factor f of the earlier work). Values of the top heat loss factor calculated by this simple technique are within 3 percent (maximum error) of those obtained by iterative solution of the heat balance equations. There is an improvement in accuracy by a factor greater than five over the current semi-empirical equations. The range of variables covered is 50° C to 150° C in absorber plate temperature, 0.1 to 0.95 in absorber coating emittance, and 5 W/m2C to 45 W/m2C in wind heat-transfer coefficient. The effect of variation in air properties with temperature has been taken into account.