Micro-channel heat exchangers, defrosting, heat pump
Micro-channel heat exchangers (MCHE) are used in automobile applications due to their low weight and high compactness. Those MCHE are just gaining interest in stationary application and they have a great potential for low heating capacity heat pumps to be installed in “passive houses” where the heating demand is 3 to 5 times lower than in the current new individual houses built in European countries. In this paper, a low capacity integrated air to air heat pump prototype is used to perform an experimental comparison of both a round finned tube and a MCHE used as an evaporator. The MCHE is a prototype one using flat fins. The comparison is based on a constant face surface criterion and an equivalent cooling capacity for different inlet temperature and air flow rate conditions. R-134a is the refrigerant used in the heat pump. First, both evaporators performances are compared experimentally and the results show a clear advantage for the MCHE. In a second step, the behavior of the MCHE evaporator is studied under frosting conditions. The frosting kinetics and the defrosting behavior are analyzed. The results show a behavior similar to round tube finned heat exchangers, with frosting cycle higher than 45 min and a defrosting, using ventilation exhaust air, in less than 10 min.