In part two and five of the standard series ISO 9459, two possibilities for performance testing of domestic solar thermal hot water systems are described.

With the CSTG (Complete System Testing Group) test method standardized in ISO 9495-2, only solar thermal systems without an integrated auxiliary heating element can be tested. The per­formance determination according to the CSTG method focuses only on sums of energy. For per­formance testing of solar hot water system according to the CSTG method, the solar irradiance dur­ing each test day is summed up. In a second step, the useful energy withdrawn from the system at the end of the day is calculated based on measurements of the fluid inlet and outlet temperatures and flow rate. Finally the withdrawn daily energy is divided by the daily solar irradiance. This test is performed for several days with different irradiance values. Based on the results obtained in this way the annual system performance can be calculated for specific reference conditions.

During the test of the system according to the DST-method (Dynamic System Test) standard­ised in ISO 9495-5 the system is operated for several days according to well specified test condi­tions. From the measured data recorded during this short-term test, specific system parameters are determined by means of parameter identification. Based on these parameters the thermal perform­ance of the system can be determined for specified reference conditions by means of annual system simulations.