Experimental evaluation of different refrigeration system configurations using CO2-based blends as refrigerants

Recently, blends created by mixing CO2 with another fluid with a higher critical temperature are being considered, to allow subcritical operation at high outdoor temperature, thus increasing the COP. The goal of this work is to evaluate through an experimental approach the energy performance of the mixture CO2/R152a. Two compositions, (95/5% and 90/10%) were tested in a single-stage refrigeration plant with and without an internal heat exchanger, and their performance is compared to that with pure CO2. Several secondary fluid inlet temperature values at the gas cooler/condenser are considered (20-25-30-35-40°C), while the inlet temperature of the secondary fluid at the evaporator is maintained at 2.5°C. Using the investigated mixtures an enhancement of the COP compared to pure CO2 is observed, when the base cycle is implemented, for temperatures above 25ºC, reaching the largest increment at highest secondary fluid inlet temperature. Instead, when using the IHX, no improvement in the COP is obtained.