Abstract
We performed numerical thermodynamic analyses of 3 multi-pressure vapor compression system configurations (cascaded, with flash tank, and with ejector) to evaluate their coefficient of performance improvements in combined cooling and heating applications. Six refrigerants were evaluated, and 25 temperature pairs of −15 °C to 25 °C cooling and 45 °C to 85 °C heating were specified. Critical parameters of the 3 configurations were varied for performance optimization. The compressor outlet temperature was constrained to prevent lubricant breakdown in actual implementation. Maximum performance improvements of 34.41 %, 39.20 %, and 46.34 % for the cascade, with flash tank, and with ejector systems, respectively, were attained. Moreover, the total number of temperature pairs exceeding the temperature limit was reduced from 19/25 to 17/25, 1/25, and 9/25 for the cascade, with flash tank, and with ejector systems, respectively. The best refrigerants to use were found to be Ammonia or R245fa as the low-pressure loop refrigerant with R245fa as the high-pressure loop refrigerant for cascade systems, Ammonia or R245fa for systems with flash tank, and R245fa for systems with ejector. This work demonstrated and quantified the ability of multi pressure configurations to increase the performance of vapor compression systems in simultaneous cooling and heating applications.
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