ENERGY ANALYSIS OF A WATER-LOOP SELF-CONTAINED SYSTEM VS A MULTIPLEX SUPERMARKET

Supermarkets are probably the largest energy users in the commercial sector and are responsible for considerable CO2 emissions. A typical supermarket may consume on the order of million kWh annually. One of the largest uses of energy is for refrigeration, which can be as much as half of the store total. In most cases, refrigeration systems employ direct expansion air refrigerant coils as the evaporators in display cases and coolers. Compressors and condensers are kept in a remote machine room located in the back or on the roof of the store. As a consequence, large amount of refrigerant is needed to charge the refrigeration system, on the order of thousand kg. Furthermore, a significant risk of important annual leakages (on the order of ten percent of the total charge annually) is a consequence of the large number of piping and pipe joints used. Nowadays advanced supermarket systems can reduce both annual energy consumption and total equivalent warming impact (TEWI). One of these advanced solutions is the water-loop self-contained refrigeration system with modulating compressors (WLSC). In this paper a real WLSC supermarket located in Italy is considered and its performances during the summer period are analyzed and compared with those of a simulated multiplex benchmark solution with fixed evaporation and condensation pressures and thermostatic expansion valve. The comparison shows that the WLSC system leads to a 12.6% electric energy reduction. The main advantage comes from the possibility to decrease the average compression ratio when modulation is required. Moreover the WLSC solution lets a 71% 15-year TEWI reduction, which is mainly possible thanks to drastic reductions of both refrigerant charge and leakages.