Low GWP Refrigerants Modelling Study for a Room Air Conditioner Having Microchannel Heat Exchangers

Microchannel heat exchangers (MHX) have found great successes in residential and commercial applications, being compact heat exchangers, to reduce refrigerant charge and material cost. This investigation aims to extend the application of MHXs as evaporators in split, room air conditioners (RAC), per fundamental heat exchanger and system modelling, and field study. Â For this paper, a microchannel evaporator model was developed, using a segment-to-segment modelling approach. The microchannel evaporator model was integrated to a system design model having a compressor, fin-and-tube condenser coil, and lines. The system model is able to predict the performance indices, such as cooling capacity, efficiency, sensible heat ratio, etc. In addition, field investigations were conducted to compare performances of two 2-ton RACs, using R22 refrigerant. The two RACs are identical, except one of them was modified by replacing the original fin-and-tube evaporator with a microchannel heat exchanger. The field testing data was used to calibrate the component and the system models. Based on the field testing and modelling studies, performances of the fin-and-tube evaporator and micro-channel evaporator will be compared. Using the calibrated system and heat exchanger models, we evaluated numerous low GWP (global warming potential) refrigerants to find a replacement for R22, i.e. propane, R32, etc. The predicted system performance indices, e.g. cooling efficiency, compressor discharge temperature, and required compressor displacement volume etc., are compared. A suitable replacement of R22 for the room air conditioner application is recommended