Study on a supercritical CO2 solar water heater system induced by the natural circulation

Abstract

This article proposes a solar water heater system induced by natural convective flow using supercritical CO2 as a working fluid. In order to investigate the characteristics of the system, the dynamic characteristics and heat transfer property of the supercritical CO2 flow are measured under variable ambient conditions. The performance parameters such as the heat recovery efficiency, effective energy efficiency ratio, effective energy efficiency, highest temperature of the water, and the amount of hot water supplied by this heater system are presented and analyzed in detail. The effects of weather and season on the system performance are respectively examined. Furthermore, the methods to obtain higher efficiency of the system are also studied. The current results indicate that the circulation of supercritical CO2 flow in this solar heater system can be easily induced by natural convection. Without a driving pump, the highest heat recovery efficiency can be up to 90.4%, which is higher than the efficiencies of other conventional solar water heater systems. It is also found that the natural convection in the system is mainly affected by the intensity, stability, and continuity of solar radiation in a day. Furthermore, the amount of hot water supplied by this system is adequate for an ordinary house-hold usage with the highest temperature of the hot water in summer being 78°C.