Modeling of a CO2-Based Integrated Refrigeration System for Supermarkets

An integrated energy system that consists of a centralized refrigeration unit can deliver the entire HVAC&R (heating, ventilation, air conditioning, and refrigeration) demand for a supermarket. CO2 (R744) is a natural refrigerant that is becoming increasingly popular for these centralized units due to significant energy and cost savings, while also being sustainable, safe, and non-toxic. This study focuses on the fully integrated CO2 refrigeration system configuration for a supermarket in Porto de Mos, Portugal, which was equipped and fully monitored through the EU-funded project MultiPACK. A dynamic system model was developed in Modelica and validated against measurement data from the site recorded for one week. The model is used to provide additional ejector performance data supporting the obtained measurement data and to evaluate the system configuration at equivalent boundary conditions. The simulation results show that the installation of a vapor ejector (high-pressure lift) is sufficient to improve the efficiency of the unit compared to an ejector-less (high-pressure valve) system. However, more notable enhancements are achieved by including additional flooded evaporation with liquid ejectors and smart regulation of the receiver pressure, adding up to a global efficiency increase of 15% if compared to the high-pressure valve system during the validation week.