This part of IS0 9459 establishes a uniform indoor test method for rating solar domestic water heating systems for thermal performance, under benchmark conditions. It applies only to solar water heating systems designed solely to heat potable water to be supplied for domestic water usage. The test procedures described in this part of IS0 9459 are applicable to systems of solar storage capacity of 0,6 m3 or less. It includes procedures for testing solar domestic hot water systems either with solar irradiance simulators or thermal simulation (nonirradiated) methods. The test procedures in this part of IS0 9459 which employ a non-irradiated solar collector array in series with a conventional heat source do not apply to integral collector storage systems, nor to systems in which thermosiphon flow occurs, nor to any system employing a collector/heat transfer fluid combination which cannot be tested in accordance with the collector test. The test procedures in this part of IS0 9459 do not require the solar water heating system to be subjected to freezing conditions. Consequently, the energy consumed or lost by a system while operating in the freeze-protection mode is not determined. This part of IS0 9459 is not generally applicable to concentrating or evacuated tube systems, unless the collimation requirements of 6.3.1.3 are met.