Edinburgh Napier University

  The system under consideration comprises a new freeze tolerant flat plate collector connected directly to a domestic hot water storage tank. Water is circulated by means of a small 12 V DC pump, driven directly by a PV module. It is desired that the system will operate with a variable low flow to provide a relatively constant outlet temperature and promote thermal stratification in the storage tank. The rationale behind employing this operational strategy is outlined, and an overview of the benefits of employing such a system is given.In respect of controlling the flow to optimize the performance of the present system, through a thorough examination of their respective characteristics and interactions, the process of selecting the most suitable combination of system components is highlighted. Furthermore, a method for determining the degree of PV output control that is required to best meet the optimum operating condition is given. System performance is then analyzed in relation to the desired operating condition. For a given pump and hydraulic system, an algorithm for predicting the collector outlet temperature in relation to the peak PV output, degree of control, collector efficiency characteristics and irradiance is presented. Predicted and measured outlet temperatures are compared, and the results discussed.