R744 Booster integrated system for full heating supply to supermarkets

In warm climates carbon dioxide (R744) refrigeration systems are known to perform worse because of the transcritical operation which occurs for a large part of the year, increasing substantially their energy use. On the other hand, the high discharge temperature potentially allows recovering a large amount of heat at various temperature levels. This paper investigates the energy performance of a R744 refrigeration system which provides a medium-sized supermarket with DHW and space heating, besides satisfying the cooling load required by the chilled and frozen food storage and display equipment. The system is controlled to meet the full heating demand of the building and is equipped with an additional air-cooled evaporator, which can be used as a supplemental heat source. Dynamic simulations of the refrigeration system, including mutual interactions with the building and the HVAC, are carried out at three climate conditions. The results are compared to alternative refrigeration systems not controlled by the heating demand, such as the R744 booster system itself, a R404A direct expansion system and a R134a/R744 cascade system, where heat pumps are employed for heating. Energy saving was predicted both when compared to the CO2 system (up to 4.5 %), and to the HFC systems (up to 16 %). Furthermore, the heating COP of the integrated system appears to be always higher than that of standalone heat pumps. The comparison shows that heat recovery can fully supply refrigeration and heating needs of the supermarket with reduced running and possibly investment costs when compared to separate systems.