Performance Evaluation of a R744 Booster System for Supermarket Refrigeration, Heating and DHW

Carbon dioxide is an eco-friendly refrigerant which is non-flammable and non-toxic. Due to its low critical temperature, transcritical operations in CO2 refrigeration systems can commonly take place. In these conditions, favourable thermo-physical properties of R744 allow heat recovery at high temperature in the high pressure heat exchanger (gas cooler) to cover domestic hot water (DHW) and heating needs. The investigated solution is a R744 booster refrigeration system operating in mild climates, which provides the selected supermarket with DHW and heating, besides satisfying the cooling load required by display cabinets and cold rooms. To meet the full heating load of the building in any operating conditions, an additional air-cooled evaporator can be used as a supplemental heat source, driving to an increment in the total energy consumption. This paper investigates a suitable control strategy for the chosen system in order to minimize the consumption and, contemporary, supply both the cooling and heating loads.