Performance analysis of two-stage CO2 transcritical refrigeration cycles with absorption subcooling and mechanical recooling

Abstract

Although the two-stage CO2 transcritical refrigeration cycle with dedicated absorption subcooling is favorable for energy saving through employing the heat to reduce the loss of throttling processes, some important issues are essential to address exactly for the performance improvement, e.g., extending the working range of heat sources and enhancing the efficiency for the mid-temperature heat utilization. Thus, the two-stage CO2 transcritical refrigeration cycle with dedicated absorption subcooling and mechanical recooling is presented and studied thermodynamically. Two kinds of the proposed system are considered, e.g., sole-subcooler for the low-temperature heat source (the scheme A) and dual-subcooler for the mid temperature one (the scheme B). The performance of the proposed system and traditional one is compared, and the effect of critical parameters on the novel cycle is analyzed in detail. For the scheme A, the lower limit of heat source temperature is extended from 80 °C to 77 °C, and the compressor power goes down by 3.3%. For the scheme B, the lower limit of heat source temperature is extended from 139 °C to 128 °C, and the power consumption is reduced by 6%. Moreover, the payback period of the scheme A and scheme B is 7.9 years and 6.4 years, respectively. The paper is helpful to increase the performance of two-stage CO2 refrigeration cycle through the heat recovery and utilization, and promote the energy saving of cold storages.