Abstract
Solar Water Heating (SWH) systems have been extensively investigated during the past decades to optimize their performance and configuration. In fact, a lot of research work has been conducted to improve the SWH system components such as the solar collector and heat transfer fluids while less studies have been devoted to improving performance through control strategies. In this paper, a comprehensive comparison and control are introduced for four configurations of SWH systems to investigate their performance under different solar radiation conditions. It is, in fact, a great challenge to regulate the outlet temperature of a SWH system under a time-varying solar radiation during the day. Hence, two controllers, namely robust and Proportional-Integral-Derivative (PID), are utilized to work in harmony in order to control the water temperatures of four SWH systems under clear and cloudy skies solar radiation conditions. Various open- and closed-loop tests are conducted, in simulation, on the proposed four SWH systems to compare their responses in terms of regulating the outlet water temperature to a desired level with a minimum energy consumption. The simulation results show the effectiveness of the proposed closed-loop control algorithms in regulating the outlet water temperature in the presence of time-varying solar radiation. Moreover, the results also show that energy consumed within the closed-loop system was 14%, 67%, 36%, and 44% less than the energy consumed within the open-loop system 1, 2, 3, and 4, respectively, under clear sky solar radiation condition. On the other hand, the energy consumed within the closed-loop system was 23%, 88%, 52%, and 58% less than the energy consumed within the open-loop system 1, 2, 3, and 4, respectively, under cloudy sky solar radiation condition. This confirms the superiority of the closed-loop system performance over the open-loop system performance. Furthermore, the results of this study show that the optimal SWH system configuration depends on the dominant nature of the solar radiation in the region at which the SWH system is installed.