Investigation on a Hybrid Single/Double Effect Solar Absorption Cooling System Driven by Fresnel Solar Collector with Thermal Storage

摘要

A solar energy system would generally be more cost-effective if it were used to provide both heating and cooling requirements in the building it serves. The aim of this study is to investigate a solar single/double effect LiBr-H2O absorption chiller driven by Fresnel solar collector with thermal storage. The studied LiBr-H2O absorption chiller can be altered between the double effect and single effect modes automatically, depending on the driving temperature provided by the solar collectors. It is designed that the absorption chiller will operate in double effect mode when the hot water temperature is higher than 150°C, and will be run in single effect mode when the hot water temperature is lower than 135°C. In this way, the solar thermal energy can be used more efficiently for cooling, i.e. the average COP of the unit is higher than that of the single effect absorption unit and the time for producing cooling is longer than that of the double effect unit. Moreover, by using the specially developed Fresnel solar collector, the solar collection section can provide thermal energy at higher temperature level compared to the normal evacuated tube solar collectors. To offset the negative effect of solar intermittence because of the weather conditions, the changing of day and night, molten-salt storage unit is installed for supporting 2 hours operation of the absorption chiller. The solar system will be used in an office building in Shanghai. It is expected that this kind of solar collector can work steadily at temperature over 150～200°C using thermal oil as the working fluid which transfer the heat to hot water through a heat exchanger, and the thermal conversion efficiency is about 40～50%, the total installation area is about 550 m~2. The daily average COP of the studied solar absorption cooling system can be about 0.8, and can produce cooling for 6-8 hours relying purely on solar energy during a typical sunny day.