A Modified Efficiency Equation of Solar Collectors

This paper describes the derivation of a modified equation for solar collector efficiency that is expressed using the heating load term instead of the inlet fluid temperature term from the currently used linear collector efficiency equation. The parameters in the modified equation are estimated using test data measured for 14 days. In evaluation of the equation's validity, the calculated daily collector efficiency agrees well with the measured daily collector efficiency, with a correlation coefficient of 0.9110. The equation is also be expressed in another form by including the term for the shape of the hot water storage tank in the solar heating system. Collector efficiencies with parametric changes are calculated with the estimated parameters and compared with different global solar irradiance on solar collectors, daily average ambient temperature and heating loads per collector area. It would be necessary to estimate the parameters for better performance of the efficiency equation with more data from long-term system simulations at various operating conditions.