This proposed revision would bring ASHRAE Standard 93 into agreement with ISO Standard 9806-1. The test procedure for performance remains the same as in previous editions, but additional methods for calculating performance efficiency from the recorded data have been added. Whereas performance was previously calculated based on gross area and inlet fluid temperature, in this revision three new methods of calculation are provided. Standard 93 provides a test procedure whereby solar energy collectors can be tested both indoors and outdoors.