This standard applies to nonconcentrating and concentrating solar collectors in which a fluid enters the collector through a single inlet and leaves the collector through a single outlet. Collectors containing more than one inlet and more than one outlet may be tested according to this standard provided that the external piping or ducting can be connected so as to provide effectively a single inlet and a single outlet. The heat transfer fluid may be either a liquid or a gas but not a mixture of the two phases. This standard contains methods for conducting tests outdoors under natural solar irradiance and for conducting tests indoors under simulated solar irradiance. This standard provides test methods and calculation procedures for determining steady-state and quasi-steadystate thermal performance@ time@ and angular response characteristics of solar collectors. This standard is not applicable to those collectors in which the thermal storage unit is an integral part of the collector to such an extent that the collection process and the storage process cannot be separated for the purpose of making measurements of these two processes. This standard does not apply to: (a) those unglazed solar collectors that can be tested in accordance with ASHRAE Standard 1980 (RA 89)1 and (b) those collectors in which the heat transfer fluid changes phase and can be tested in accordance with ASHRAE Standard 109-1986 (RA 2003).2 However@ a suggested test procedure is given in Appendix for those phase-change collectors with an integral heat exchanger that satisfy specifications 2.1 and 2.2 and are excluded in the scope of ASHRAE Standard 109-1986 (RA 2003).2 PURPOSE The purpose of this standard is to provide test methods for determining the thermal performance of solar energy collectors that use single-phase fluids and have no significant internal energy storage. I