Design and testing of a microchannel heat exchanger working as condenser and evaporator

In the recent years, international agreements and regulations push for a reduction of production and utilization of Hydrofluorocarbons (HFCs), while achieving high efficiency remains a crucial aspect for refrigeration and air conditioning systems. One of the possible candidates to replace the high global warming potential (GWP) fluid currently employed in heat pump systems (R410A) is the refrigerant R32, which belongs to A2L class. In addition to adopting low-GWP refrigerants, charge minimization is a major design objective for such systems, mainly in the case of flammable refrigerants. In the case of reversible heat pumps, a reduced volume of the heat exchangers limits the refrigerant charge migration between condenser and evaporator when switching between the operation modes. The refrigerant charge minimization coupled with the use of new refrigerants can therefore be considered one of the most important objectives for new heat pump developments. The microchannel technology helps for this purpose. The present paper presents an air-to-refrigerant microchannel heat exchanger working with R32, realized in the framework of the European Project GEOTeCH. The prototype heat exchanger, working both as the condenser and as the evaporator, has been tested on a dual source (air and ground) heat pump, which can operate in heating and cooling modes. A model of the microchannel heat exchanger has also been developed and the predicted performance have been compared with the experimental measurements. In the end, the model has been used to estimate the refrigerant charge trapped in the minichannel when it works as the condenser and the results have been compared with those obtained using a traditional finned coil heat exchanger.