Today’s rising electricity costs have put refrigeration efficiency back on the manager’s wish list for small and medium-sized stores. In the past decade, the higher installation costs and engineering costs have driven many owners away from efficient central refrigeration systems and toward less efficient self-contained freezers and refrigerators.
Self-contained refrigerators and freezers use at least 25% more electricity than central systems. If these individual condensers and compressors are located inside the store, they make noise and increase air-conditioning costs by releasing heat into the store. Compressors of self-contained units die younger because they cycle more frequently. Short cycling is both inefficient and destructive to compressors and their controls.
A centralized refrigeration system can serve multiple refrigeration units and also provide air conditioning. If you are considering central refrigeration, don’t worry if you own some self-contained cases. Simply remove their compressors and condensers, and connect the evaporators to your new central system.
The best central systems feature multiple compressors, computerized controls and a heat-recovery system to heat the store’s water. A heat-recovery system provides both free water-heating energy and additional cooling capacity for stores with delicatessens and meat departments that use a lot of hot water.
For a small store, a two-compressor system with unequal-sized compressors permits three compressor-power levels for differing outdoor temperatures. One of these levels is well matched for current refrigeration load, and therefore the compressor’s cycles are long and efficient.
Most compressors operate at a constant high pressure, which is inefficient because high pressure isn’t needed during cool weather. Variable-pressure control strategies, known as floating head pressure and floating suction pressure, can save up to 15% over constant-pressure control.
Over-sized evaporators and condensers enhance refrigeration efficiency because their greater surface area can transfer heat at more moderate pressures and temperatures, compared to smaller coils. Used evaporator and condenser coils are often available at reasonable prices, making it more affordable to invest in larger coils.
Anti-sweat heaters, which prevent fogging in glass-door freezers and refrigerators, draw a lot of power and operate constantly in most stores. Humidity-sensing controls significantly reduce the operating time of anti-sweat door heaters and defrosters, if your HVAC system can limit relative humidity to 40% or less as experts recommend. Computerized energy-management systems for grocery and convenience stores can control store lights, heating, air conditioning, case lighting, compressor pressure, defrost controls, and anti-sweat heaters.