Testing Evaluates the Performance of a Refrigerated Display Case
For supermarkets, refrigeration accounts for more than 50 percent of the annual electric energy costs. In these typical stores, the compressors serving medium temperature display cases represent up to 20 percent of the energy costs.
Southern California Edison's Refrigeration and Thermal Test Center (RTTC) evaluated the performance and energy use of a 20-foot-long, multi-deck, medium temperature display case by systematically varying and controlling the following operating conditions:
- Indoor relative humidity
- Indoor dry bulb temperature
- Fan motor efficiency
- Product loading arrangement
Also tested was the impact of air curtain agitation, represented by shopper traffic, on the energy use of the case.
Indoor relative humidity had, by far, the largest impact on the energy use of the display case. Increasing indoor wet bulb temperature (which reflects an increase in relative humidity) by 10oF resulted in a 25 percent increase in compressor power use.
An increase in indoor dry bulb temperature also produced an increase in the energy use of the display case. However, a one degree Fahrenheit (1oF) increase in indoor temperature resulted in only a one percent increase in compressor power use.
The more common, non-uniform, loading arrangements seen in supermarkets (such as shelves over-filled, gaps in other shelves, and return air flow partially blocked), impacted the product core temperature significantly, increasing it by two degrees Fahrenheit (2oF).
