Song, X., Fortier, R., and Sarnia, S., "Underhood Air Duct Design to Improve A/C System Performance by Minimizing Hot Air Recirculation," SAE Int. J. Passeng. Cars - Mech. Syst. 8(1):338-345, 2015, doi:10.4271/2015-01-1689.
The underhood hot air recirculation greatly impacts A/C system performance at idle and low vehicle speed conditions. The hot air recirculation can raise condenser inlet air temperature in some cases as much as 18°C above ambient, which lowers condenser cooling capacity and increases compressor work. Underhood airflow research in the following study suggests that a properly designed air duct is able to minimize hot air recirculation and improve the Compressors Coefficient of Performance (COP) at idle by 27%. This paper discusses underhood hot air recirculation testing methods, airflow distribution, air duct design concepts, as well as the cross wind and wind tunnel effects. This dedicated air duct design indicates it should improve A/C emissions, which could contribute to meeting the Environmental Protection Agency's (EPA) Green House Gas Emissions Regulations in North America.