Display Case Shield Reduces Supermarket Energy Use
 Supermarkets operate on a narrow profit margin and refrigeration is the largest component of their electric energy usage. Therefore, a reduction in refrigeration load lowers energy costs and improves competitiveness. Furthermore, increasing product shelf life will enhance profit margin. As a result, knowing the impact of devices such as aluminum shields, used in open display cases during non-business hours, is advantageous to supermarket owners and managers.
Southern California Edison (SCE) tested and evaluated the impact of low-emissivity aluminum shields on the power consumption and thermal performance of a multi-deck display case, commonly used in supermarkets for storing and refrigerating dairy products. The display case was tested in a controlled environment chamber at SCE's Refrigeration Technology and Test Center (RTTC).
Thermal radiation and convection of warm air into the cold display case accounts for most of its refrigeration load. Aluminum shields can be utilized to cover the front opening of the display case and reduce the radiation and convective heat transfer into the case, thereby reducing the power consumption while improving the product temperature uniformity and shelf life. RTTC's monitoring equipment tracked the refrigeration system's temperature and pressure points during the operating hours of three typical supermarket scenarios:
- Scenario 1 - Base-case: Non-24-hour store with no shields applied during closing hours
- Scenario 2 - Night: Non-24-hour store with shields applied for 6 hours during night closing
- Scenario 3 - Holiday: Store closed for 24 hours with shields applied for 24 hours
Testing for scenario 2 revealed that the low-emissivity shields reduced the refrigeration load by 8.5 percent and the compressor power by 9 percent. In scenario 3 the performance of the shields reduced the refrigeration load by 41 percent and the compressor power by 36 percent. With the shields in place, the average product temperature was as much as 5oF colder on the lower shelves. |
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