HVAC coverage in integrated refrigeration systems at various climate and building conditions

Food retail applications offer a unique opportunity to improve the performance of pure CO2 refrigeration sys- tems, i.e. the integration of all the thermal functions in a compact “fully-integrated” unit, capable of providing refrigeration capacity at two temperature levels for chilled and frozen products, hot water production, space heating and cooling for the supermarket. Many factors determine the economic advantage of such a solution. A case study of a transcritical CO2 integrated refrigeration system for a 1200 m2 supermarket with back up heat pumps is taken as an example and several scenarios are investigated. A comprehensive model in TRNSYS with in- house types, validated with field data from a fully instrumented plant located in Northern Italy, allows a thermal dynamic simulation of the building with its interaction with display cabinets, the estimation of the refrigerating loads of display cabinets and cold rooms, and the behaviour of the commercial refrigeration unit and heat pumps. The goal is to investigate the coverage limits and global energy use for six climate zones and various load ratios, thus considering also different sales areas and construction types of the building. It is proven that such integrated solution can effectively cover also space cooling needs in a range from 95 to 100 % and space heating from 83 % to 100 %, provided an additional outside evaporator is installed especially for coldest climates and higher heating requests. In all but one case, the integrated system is more advantageous than the separate solution, with total electrical energy savings ranging from a few percentage points to 10.5 %.