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

An improved equation form for computing the glass cover temperature of flat-place 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 degrees C to 45 degrees C. In this extended range of variables the errors due to simplified method based on empirical relations for U-t are substantially higher. (C) 1999 Elsevier Science Ltd. All rights reserved.