Evaluation and control of thermal losses and solar fraction in a hot water solar system

Water heating for domestic needs contributes significantly to energy demands in the residential sector. The paper reports an energetic analysis of a solar hot water system performed on a dwelling located in different European cities. The study is focused on a group of apartments, where the domestic hot water is provided by a solar system coupled with a storage tank. A recirculation loop, composed by a pump and a system of pipes from the tank to the more distant apartment is also considered in the study. The loop overcomes the problem of long waiting times for hot water for the user by keeping it flowing inside the system. Since the recirculation loop is compulsory in this kind of plants, a dynamic energetic analysis is performed in order to analyze the pipe heat loss influence on the solar fraction. Dynamic simulations are performed using TRNSYS by interrupting the flow in the recirculation loop during the night and monitoring the temperature in the circulation loop. The study shows the sizing process of the whole system, the variation of the solar fraction and heat loss fraction for all the analyzed cases.