Supermarkets use tremendous amounts of electricity. A 50,000 square foot store can have peak electrical loads greater than 500 kW. Approximately half this power is used to cool refrigerated display cases.
A store's refrigeration system must continually pump the heat that the cool display case gains from the warmer store to the outdoors. In effect the refrigerated display cases are air conditioning the store providing both sensible and latent cooling. But they provide this cooling at a very poor efficiency. This is because almost all the evaporators in these display cases are running at a much lower temperature than a conventional HVAC cooling system (e.g., the evaporators for display cases for frozen foods can run as low as -25 F and for non-frozen product, between 20 F and 35 F versus 45 F to 50 F for the evaporator of the store's air conditioner). A refrigeration system's compressor must work harder, and less efficiently, when it pumps heat over a larger temperature rise.
Any measures that reduce the heat gained by the refrigerated display cases will save electricity for the store. As shown in tests by the Refrigeration and Thermal Test Center (RTTC) at Southern California Edison, a 1 F drop in store temperature will reduce the heat gained by the display case and lower compressor power by 1%. However, saving energy by reducing the store's temperature has its limits since customers must be comfortable in the store.