Air conditioning is required for both customer comfort and proper operation of the refrigerated display cases. Unlike most stores that focus on temperature control alone, supermarkets emphasize dehumidification. Experience indicates the optimum balance is where the relative humidity is maintained between 40 and 45%, a significant variation from the typical retail store that operates in the 50 to 56% range. This range reduces energy use while maintaining product appearance and quality, reduces frost, and keeps case glass surfaces clear.
Humidity control in the supermarket is a key element in the energy consumption of the supermarket. If the humidity is too high, the refrigeration evaporators frost up quickly and anti-sweat heaters on case doors and other surfaces operate longer, increasing refrigeration energy use (as well as the energy used in anti-sweat heaters). If the humidity is too low, food produce wilts, requiring more water spraying and thereby raising the humidity again. While the frost buildup tends to control moisture in the air, it is an expensive way to provide dehumidification. The most efficient humidity control is through the air conditioning system.
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