Modelling commercial refrigeration systems coupled with water storage to improve energy efficiency and perform heat recovery

• CO2 refrigerating plants in mild climates are feasible and energetically acceptable.
• Synergy between commercial refrigeration and HVAC plants allows energy savings.
• Heat storage allows a considerable heat recovery in favour of space heating.
• Modelling is essential for an effective design of heat recovery solutions.

A basic CO2 transcritical/subcritical commercial refrigeration system is considered, applied to cold rooms and display cabinets in a supermarket. Subcooling of the refrigerant or heat recovery from condensation can be performed, taking advantage of a large fire prevention water tank. The whole refrigeration system is modelled in a TRNSYS environment, taking into account the hourly weather data and calculating the hourly cooling load demand from display cabinets and cold rooms equipment. New types have been written to describe display cabinets and cold rooms, CO2 refrigerating units and a particular water store.Simulations consider a simple double compression cycle with liquid receiver, and other options among which an auxiliary compressor. Results show that CO2 plants are feasible and energetically acceptable in mild climates, provided that improvements to standard cycle are adopted. Furthermore, heat recovery can be effectively performed through the employment of a heat storage.