Condenser subcooling, alternative refrigerants (R1234yf), COP improvements
The difference in effect of subcooling in a condenser (non-designated area, NDA) vs. in a subcooler (designated area of the same condenser, DA) on the system performance is experimentally analyzed in a vehicular air conditioning system operating with R134a and R1234yf. With a unique set of microchannel condensers, an experimental comparison between subcooling generated in non-designated area (NDA) and designated area (DA) of the condenser showed that both configurations yielded similar values of maximum COP improvement within the operating conditions considered. The results suggested that the way condenser subcooling is achieved, either in a DA or a NDA, may not be important in terms of COP. The experimental results for non-designated subcooling indicated that the larger the air-refrigerant temperature difference in the condenser, due to a large cooling capacity needed for a given condenser size, the higher the COP maximizing subcooling and the maximum COP improvement from condenser subcooling. For R1234yf, as the temperature difference in the condenser increased from 12°C to 28°C, the COP maximizing subcooling increased from 6°C to 16°C and the COP gains, from 6% to 44%. Experimental and numerical results also demonstrated that condensers with a higher air-refrigerant temperature difference in the condenser would require a larger COP maximizing area ratio allocated for subcooling. Nevertheless, a fixed designated area yielded near maximum COPs within a reasonable range of operating conditions.