Effects of indoor relative humidity on refrigerated display case performance

Refrigerated display cases are normally rated at a store environment of 24P0PC (75P0PF) and a relative humidity of 55%. If the store can be maintained at lower relative humidities, significant quantities of compressor energy, defrost energy and anti-condensation heater energy can be saved. In this study a model was developed for a 4650 mP2P (50,000 ftP2P) food store with a typical mix and quantity of refrigerated display cases. Moisture balances were done for a typical day in a typical store for each month of the year yielding a twenty-four hour variation in the store relative humidity. Using these calculated hourly values of relative humidity for a 24 hour typical day, the store relative humidity distribution was calculated for a full year of store operation in Tampa, Florida. Savings of 10% in annual display case operating costs were found for changes of 5 percent in the store relative humidity for the Tampa, Florida region. The total store energy bill (display cases, air-conditioning and lights) would be reduced by 4.7% for this 5% change in relative humidity. These are significant cost savings for a supermarket.