Control strategies of CO₂ refrigeration / heat pump system for supermarkets

CO2 is a promising refrigerant compared to traditional HFCs due to its insignificant global warming potential and nonthreatening to the ozone layer. It has been used as refrigerant in industrial and commercial refrigeration in recent years. With high compactness and the ability to recover heat, CO2 booster systems have been widely installed in newly constructed supermarkets in the Netherlands. One remarkable advantage of this system is that great amount of heat can be recovered from the gas cooler for heating use due to high temperature driving force from CO2. Sometimes the COP is sacrificed to fully satisfy the heating demand. Within the present work, a quasi-steady-state computer model has been developed to study the performance of the system based on a typical Dutch supermarket. The model has been validated using experimental data. By altering condensing pressure and gas cooler capacity using different methods, various control strategies to satisfy both cooling and heating demand have been proposed and compared. The results from the simulation illustrate that some control strategies have lower energy consumption and easier operation compared to the others. The study also shows that CO2 booster refrigeration system has a good potential for heat recovery. It has the potential to save 13% primary energy compared to conventional heating method in supermarkets.