This Standard sets out a method of determining the annual performance of domestic solar and heat pump water heaters using a combination of test results for component performance and a mathematical model to determine an annual load cycle task performance. The Standard also defines a procedure for evaluating the task performance of conventional domestic water heaters so that the energy savings of solar and heat pump water heaters can be evaluated relative to conventional water heaters operated under the
same annual task load.

Testing of solar water heating systems under outdoor or indoor solar irradiance conditions has been defined in AS 2984 — 1987,Solar water heaters — Methods of test for thermal performance — Outdoor test method, and A S 2813 — 1985,Solar water heaters — Methods of test for thermal performance — Simulator method. Outdoor testing requires a long test period ( 8-10 weeks) due to the need to obtain stable inputs for a range of operating conditions. Indoor testing ( solar simulator ) provides stable input conditions, however, the equipment required and operating costs are very expensive. The major draw back of the outdoor or indoor solar irradiance testing is that the test must be repeated for every variation of system configuration offered by the supplier.

The procedure defined in this Standard over comes the time and cost limitations of previous water heater performance standards and provides a procedure for calculating the purchased energy consumption of solar and heat pump domestic water heaters.

The terms ‘normative’ and ‘ informative’ have been used in this Standard to define the application of the appendix to which they apply. A ‘ normative’ appendix is an integral part of a Standard, whereas an ‘informative’ appendix is only for information and guidance.

First published as AS 4234-1994.