Two stage ecological hybrid sorption–compression refrigeration cycle

•New application of the CO2 refrigerant for subcritical cycle is shown.•Two stage hybrid ecological cycle with only natural refrigerants is tested.•There are significant energy savings compared to two stage compression cycle.•There is substantial TEWI reduction compared to two stage compression cycle.•The combination of heat pump/refrigerating operation is possible.

Low critical point of CO2 results in transcritical refrigeration cycles with low efficiency and high discharge pressure. H2O has a high triple point temperature that limits its application to temperatures above 0 °C. In this paper the two stage hybrid cycle is presented, where the Low Temperature (LT) stage is the compression cycle with CO2 and the High Temperature (HT) stage is the H2O sorption cycle. The choice between absorption and adsorption technology depends on the application and most of all is related to the temperature available for the desorber. This paper presents the adsorption technology on the HT stage powered by solar thermal energy. The combined hybrid cycle has been tested for two years at the Politechnika Krakowska, and a summary of the results is shown in this paper. The experimental results have been compared with two-refrigerants, two stage cycles and CO2 - only cycles.