Energy efficiency of a reversible refrigeration unit using R410A or R32

The aim of this article is twofold: first, to compare the performance of R410A with that of R32, which is considered a possible HFC substitute with lower global warming potential (675 instead of 2088); second, to exploit the effect of the circuit length in the finned coil of a packaged air-to-water reversible unit with given water plate heat exchanger and scroll compressor. Both scopes are pursued through the analysis of a case study, a system with nominal cooling capacity of about 74 kW at 35°C dry-bulb outdoor air temperature and a nominal heating capacity of about 70 kW at 2°C dry-bulb and 1°C wet-bulb ambient temperature. The performance of the two refrigerants inside a “real” machine is simulated by means of an advanced numerical model of a packaged reversible refrigeration unit. The system consists of a single refrigerating circuit with two identical scroll compressors. The compressor was characterized by its experimental performance curve according to Standard EN 12900 (EN 2013a) for both R410A and R32. Off-the-shelf copper tubes and louvered aluminum fins were considered for the condenser and typical brazed-plate heat exchanger for the evaporator of the chiller configuration. The finned coil heat exchanger was first thermodynamically optimized for R410A and R32 for both condenser and evaporator operation with regard to the number of internal circuits according to the total temperature penalization performance evaluation criteria (Cavallini et al. 2010; Brown et al. 2013), without changing the overall heat exchanger dimensions. The effect of finned coil circuit length on the performance of the investigated reversible unit with the two refrigerants was then analyzed at nominal design conditions and under a seasonal perspective. Based on the modeling work, it is possible to conclude that R32 system efficiency performance is acceptable as alternative to R410A for packaged air-to-water reversible unit.

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