Energy, environmental, and economic analysis of novel R744/R290 cascade refrigeration systems designed for warm ambient conditions utilizing ejector

Abstract

There is a growing global awareness about the need to reduce total carbon equivalent emissions and other environmental problems caused due to synthetic refrigerants. The study utilizes cascade refrigeration systems (CRS) with R744 in the low-temperature circuit and R290 in the high-temperature circuit. Two evaporators are present in the LTC; one is direct expansion (DX) type at −40 °C with a cooling load of 70 kW, and other is gravity-fed evaporator at −25 °C with 60 kW cooling load. The study aims to enhance the performance and economic and environmental impact of CRS by incorporating parallel compression (PC) in LTC, a gravity-fed evaporator, and an ejector in HTC. The performance is compared to a baseline CRS system using a flash-gas bypass arrangement (FGB) in the LTC, bypassing generated flash gas to compressor suction. PC in LTC removes flash gas from receiver pressure to cascade condenser pressure in the first suggested CRS. While the second proposed CRS (PCEJ) employs an ejector in HTC over and above PC in LTC. The CRSs demonstrate significant higher COP of 1.43, 1.58 and 1.65, leading to an improvement upto 62.4 %, 79 %, and 86 % over the reference HFC-404A system at 45 °C ambient temperature. SEER analysis also establishes higher year-round efficiency compared to reference HFC-404A by 22 %, 36 %, and 44 %. The total TEWI of FGB, PC, and PCEJ is 43.1 %, 53.2 %, and 53.5 % lower compared to the reference system, indicating substantial potential for lowering global warming when implemented. Economic analysis brings out relative cost comparisons under various measures.