Evaluation of Carbon Dioxide as R-22 Substitute for Residential Air-Conditioning.
Evaluation of Carbon Dioxide as R-22 Substitute for
Brown, J. S.; Kim, Y.; Domanski, P. A.
Annual Meeting, 2002. Proceedings. 2002, Honolulu, HI,
ASHRAE Transactions, Vol. 108, No. 2, 954-964.
carbon dioxide; evaluation; air conditioning;
refrigerants; equations; simulation; heat transfer
This paper compares the performance of CO2 and R-22 in
residential air-conditioning applications using
semi-theoretical vapor compression and transcritical
cycle models. The simulated R-22 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 R-22 heat exchangers employed the same
microchannel heat exchangers as CO2 with the difference
that we modified the refrigerant passages to obtain
reasonable pressure drops. The study covers several heat
exchanger sizes. The R-22 system had a significantly
better coefficient of performance (COP) than the CO2
system when equivalent heat exchangers were used in the
CO2 and R-22 systems, 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 applications. An entropy generation
analysis showed that the CO2 evaporator operated with
fewer irreversibilities than did the R-22 evaporator.
However, the CO2 gas cooler and expansion device
generated more entropy han their R-22 counterparts and
were mainly responsible for the low COP of the CO2