Experimental investigation on the use of internal heat exchangers in variable-capacity carbon dioxide refrigerating systems.

This study focuses on the use of two-stage variable-capacity carbon dioxide compressors in light commercial refrigerating systems. Tests were carried out with the same system configuration, but with and without an internal heat exchanger (iHX). It was found that the cycle without iHX reaches a maximum Coefficient of Performance (COP) with a single combination of refrigerant charge and expansion restriction at any compressor speed. It was also found that there is a compromise between the iHX effectiveness and the minimum allowed evaporator superheating value. Furthermore, it was noted that the iHX-based cycle with iHX performs better than the cycle without iHX only at the compressor speed selected for the charge and restriction optimization exercise.