Experimental and Modeling Study on Nighttime Heat Loss and Anti-Freezing Analysis of FPC Group
Abstract
The low-temperature-caused freezing of outdoor pipes and solar collectors in winter night is one of the most serious problems in solar thermal system. Studying the heat loss characteristic of the solar connector groups in nighttime is greatly significant for solar collector groups anti-freezing and maintaining system safety. In this paper, a heat loss mathematical model was established and validated through on-site measurement, to investigate the heat loss characteristic of the flat plate solar collectors (FPC) groups. Furthermore, the anti-freezing critical flow rate was analyzed when outdoor temperature and inlet water temperature vary. As an illustrative example, the anti-freezing analysis for Harbin, a northern city in China, was conducted. The results show that, the front heat loss and connecting pipes constituted the main heat loss of the solar collector group in nighttime, which accounted for 63.32% and 15.53% respectively. Besides, making anti-freezing flow rate equal to daytime working design flow rate is not suitable. Hence, the flow rate should be reduced through the water pump frequency conversion methods. Moreover, winter minimum temperature in China severe cold area can be 28.7℃. On that occasion, a single set of solar connector group should keep the inlet temperature higher than 15℃, while the flow rate larger than 0.5L/min.