Approximate method for computation of glass cover temperature and top heat-loss coefficient of solar collectors with single glazing

Abstract

An improved equation form for computing the glass cover temperature of flat-plate solar collectors with single glazing is developed. A semi-analytical correlation for the factor f—the ratio of inner to outer heat-transfer coefficients—as a function of collector parameters and atmospheric variables is obtained by regression analysis. This relation readily provides the glass cover temperature ( T g). The results are compared with those obtained by numerical solution of heat balance equations. Computational errors in T g and hence in the top heat loss coefficient ( U t) are reduced by a factor of five or more. With such low errors in computation of T g and U t, a numerical solution of heat balance equations is not required. The method is applicable over an extensive range of variables: the error in the computation of U t is within 2% with the range of air gap spacing 8 mm to 90 mm and the range of ambient temperature 0°C to 45°C. In this extended range of variables the errors due to simplified method based on empirical relations for U t are substantially higher.