The Input-Output Model for Solar Water Heaters: Model Errors and Long-Term Performance Estimate

Based on the experimentally observed linear relationship between the daily collected energy and the daily insolation, the development of a test method for the performance rating of solar water heaters is studied using both an analytical modeling of the daily performance and detailed simulation. This analysis has shown the existence of a general linear correlation between daily performance and external conditions (daily irradiation, ambient temperature, main’s water temperature, and storage initial temperature). Two approaches appeared possible for the long-term performance estimate and, for its simplicity, the statistical one was chosen for the definition of the European test method for solar water heaters, also known as the input-output test method.