Performance optimization of a transcritical CO2 supermarket refrigeration system equipped with an ice tank

Due to the low critical temperature of CO2, the CO2 supermarket refrigeration systems are often forced to operate in a transcritical regime, which results in poor energy efficiency. In order to overcome this performance penalization, the integration of an ice tank to cool down the CO2 leaving the condenser/gas cooler is considered in this work. A novel optimization method was proposed to minimize the overall energy consumption by optimally scheduling trade-off between the discharge mode and the charge mode. The solution of the optimization problem was achieved based on Particle Swarm Optimization (PSO). The proposed strategy was applied to five sample locations (Copenhagen, Birmingham, San Francisco, Sydney and New Delhi) representing different climates. The results obtained showed an energy saving ranging from 6.4 % to 7.9 % for the hottest day and from 0.4 % to 2.9 % for the entire year compared to the CO2 system without the ice tank.