Integration of a solar-powered absorption chiller for performance enhancement of a supermarket CO2 refrigeration plant

Abstract

CO2 refrigeration configurations are the most viable solution for commercial refrigeration plants, which are however accompanied with energy challenges due to their low energy efficiency when operating under high ambient temperatures. This study examines the coupling of a CO2 booster system with a solar absorption chiller, used to sub-cool the CO2 of the main cycle. The refrigeration system under study is projected to cover the cooling requirements of a supermarket refrigeration plant with an installed capacity of 80 kWR for the medium and 20 kWR for the low-temperature circuit, in the region of Athens, Greece. The investigated process involves utilization of an absorption chiller module with 60 kWR of cooling capacity working with a LiBr-H20 pair powered by heat produced in fifty evacuated-tube solar collectors with a total collecting area of 115 m2. The energy performance analysis was based on validated numerical models developed in MATLAB using the CoolProp library. Through parametric analysis the coefficient of performance (COP) of the proposed topology was compared to the COP of a conventional booster system under constant low (450 W/m2) and high (800 W/m2) incident solar radiation for the temperature range 1–40 °C, resulting in maximum COP increments of 26.44% and 47.34% respectively. Performance simulation on an annualized basis was also conducted, by using the average hourly values of ambient temperature and solar radiation for every month of the year. The results showed that in comparison to the conventional booster system, the sub-cooling rates achieved a maximum increment of COP of 47.48% hourly and 16.36% monthly for August which is the warmest month of the year. Annual electricity consumption decreased by 8.93%, resulting in an energy savings of 30.19 MWh/year.