Delicate balance between energy, exergy, cost and environmental impact in Finding sustainable cooling systems: Alternative refrigerants and advanced cycles

The energy related to using air conditioning systems accounts for 20 % of global building electricity consumption impacting the overall energy use. Moreover, the high global warming potential (GWP) of current refrigerants further contributes to climate change, with stringent policies on deploying low-GWP refrigerants in place to mitigate it. We present an energy, exergy, economic and environmental (4E) evaluation of two recently designed novel low-GWP blends 60 wt% HFO1243zf + 40 wt% R1234ze(E) (GWP < 1, KU2RV-1), and 90 wt% HFO1123 + 10 wt% R32 (GWP 70, KU2RV-2) as replacements for R134a and R410A, respectively, compared to their commercial alternatives, R513A and R32. The evaluation considers the use of the novel blends with advanced cooling cycle configuration focused on waste-heat recovery, including liquid-to-suction line heat-exchanger cycles (LL/SL-HX) and two-stage linear compressor systems (TS-VCRC), compared to the basic SS-VCRC cycle. The molecular-based soft-SAFT equation of state is used for calculating the needed thermodynamic properties. The 4E analysis also considers the geographical deployment of the systems. The use of KU2RV-1 is favorable across all 4E factors for replacing R134a, with larger potential compared to R513A. Nevertheless, R32 remains more suitable than KU2RV-2 for replacing R410A, although with larger negative environmental impact. The TS-VCRC configuration presents better energy, exergy, and environmental performance, however, at a higher cost mark-up of $66.5 – $73.0 per unit, compared to the less efficient LL/SL-HX cycle. Nonetheless, the additional cost is an acceptable compromise considering reduction in CO₂-eq emissions in range of 10.56 – 13.92 kg annually per unit when using the novel blends. This work highlights how a complete 4E analysis is needed not only for the working fluid (with low-GWP), but also the cooling cycle configuration, to find truly efficient, sustainable and affordable cooling alternatives.