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Evaluation of Carbon Dioxide as R-22 Substitute for Residential Air-Conditioning
Evaluation of Carbon Dioxide as R-22 Substitute for Residential Air-Conditioning (1.85 MB)
Brown, J. S.; Kim, Y. C. and Domanski, P. A.,
ASHRAE Transactions , June 22-26, 2002 , Honolulu, HI - June 01, 2002
Keywords:
Air conditioning , Carbon dioxide , Microchannel heat exchanger , Residential , R22 , Simulation , Transcritical cycle , Vapor compression cycle
Abstract:This paper compares performance of CO2 and R22 in residential air conditioning applications using semi-theoretical vapor compression and transcritical cycle models. The simulated R22 system had a conventional component configuration, while the CO2 system also included a liquid-line/suction-line heat exchanger. The CO2 evaporator and gas cooler were microchannel heat exchangers originally designed for CO2. The R22 heat exchangers employed the same microchannel heat exchangers as with the difference that we modified the refrigerant passages to obtain reasonable pressure drops. The study covers several sizes of heat exchangers. The R22 system had a significantly better COP than the CO2 system when equivalent heat exchangers were used in the CO2 and R22 system, which indicates that the better transport properties and compressor isentropic efficiency of CO2 did not compensate for the thermodynamic disadvantage of the transcritical cycle in comfort cooling application. The entropy generation analysis showed that the CO2 gas cooler and expansion device generated more entropy that their R22 counterparts and were mainly responsible for the low COP of the CO2 system.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899
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Last updated: 4/21/2005