Technique for evaluating steady-state conditions in flat-plate solar collector testing

Testing air- and liquid-filled solar collectors according to ANSI/ASHRAE 93-1986 (ASHRAE 1986) has proved difficult in much of the world due to the strict steady-state requirements set forth in the standard. This paper presents a method to quantify the level of quasi-steady state using the first-order time response of the collector to weigh changes in energy collected and inlet temperature. Using existing test data from 16 clear days, the method produced thermal performance curves that were statistically indeterminate from curves produced using a modified version of ANSI/ASHRAE 93-1986. Relaxing the wind and solar radiation restrictions was necessary to obtain an ANSI/ASHRAE 93-1986 plot. The method presented in this paper should significantly reduce the time required and, therefore, the costs of conducting steady-state thermal performance tests for both air- and liquid-based solar collectors.