The installation of night covers on supermarket vertical or semi-vertical display cases can reduce energy use due to reduced refrigeration, air conditioning, and heating loads. The concept is straightforward---insulated night curtains or retractable thermal shields are slid into place when the supermarket closes down for the night.
The provision of insulated night covers will increase the efficiency of horizontal refrigerated display cases. One design consists of woven aluminum covers that can be factory installed or retrofitted onto existing display cases. The back of the cover is coated with a fire retardent and the fabric is perforated for breathability and to prevent accumumlation of condensation. The cover provide an insulating thermal barrier and are designed to be easily rolled up so they are out of the way when the store is open. Secondary benefits of insulated cover use include prolonging the shelf life and appearance of perishable products, reduced condensation, reduction of produce losses due to drying and wilting, less warming and melting, and the provision of protection against short term power outages.
This technology should provide savings in all grocery stores where night covers are not currently in use. Covers can be deployed on meat, cheese, milk product, beverage, deli, floral, and produce coolers and display cases. Use of night covers prevents warm air from infiltrating into the case, prevents cold air spillage, and reflects radiated heat away from the cooler. These features produce a cooler and more stable case temperature, reducing daily produce trim and spoilage by as much as 75%.
BC Hydro's Power Smart Program installed five insulated night covers at a food wholesaler and reported energy savings of 6,800 kWh annually after installing night covers on five open coolers with a total of 211 square feet (savings of 32.2 kWh/sf-year). (PowerSmart, 2008). A Connecticut Power & Light case study that involved the installation of 48 installed night covers reported savings of about 1,360 kWh/year per cover. (Connecticut Energy Efficiency Fund, 2014).
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Baseline Description: Vertical Display Case with No Night Cover Baseline Energy Use: 16000 kWh per year per unit
BC Hydro conducted a demonstration project that installed covers on five open coolers, covering a total of 211 sf. The Energy savings were 6,800 kWh/year (or 32.2 kWh/sf). The average size of a night cover is thus 42.2 sf (approximately 6 ft x 7 ft) with the savings per cooler being about 1,360 kWh/year. (PowerSmart, 2008). Tests conducted by Southern California Edison indicate that night covers reduce refrigeration system compressor energy use by 8.5%. (Customer Success, 2014). The baseline open vertical display case energy use is estimated at 16,000 kWh/year.
Note: night covers will not provide any demand savings as they are generally employed during early morning hours. Generally, night covers might be applied for 6 hours in a 24-hour period for 2,190 hours of use per year.
"Typical" Savings: 36% Savings Range: From 8% to 50%
Savings can be expressed as a percentage of the refrigeration system load when the cover is in use, as a percentage of total refrigeration system load (which can be as much as 50% of the total supermarket electrical load) or as a percentage of total store energy consumption. The number stated here---36%---is a reduction in cooling load during the hours that the cover is deployed.
"Typical" Savings: 9% Low and High Energy Savings: 9% to 41%
Southern California Edison tested night covers at its Refrigeration Technology and Test Center in Irwindale, CA. The conducted tests for two scenarios---no insulated covers versus covers applied for six hours during the night closing. Refrigeration system loads were reduced by 8.5% when the covers were installed for a six hour period during night closing. Compressor power was reduced from 3.1 to 2.8 kW. They also found a refrigeration system energy use reduction of 41% when the night covers were left on for 24 hours (they called this a holiday scenario). (Customer Success, 2014).
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
The Food Marketing Institute (in their Industry Overview 2013, Supermarket Facts sheet) indicates that there are 37,459 supermarkets in the U.S. with annual sales of $2 million or more. Prorating by population indicates that there may be 4% x 37,459 or 1,498 large supermarkets in the Northwest. Assuming that each supermarket has a total of 20 open vertical display cases indicates a case population of 29,960 cases in the region. It is not known how many are already equipped with night covers. (Food Marketing Institute, 2013). Also unknown is the number of display cases present in small and medium-sized grocery stores.
Regional Technical Potential of an Emerging Technology is calculated as follows: Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Customer Success, 10/01/2014. Display Case Shields Reduce Supermarket Energy USe Southern California Edison
PowerSmart, 08/15/2008. Bowen Island Market's Energy-Saving Initiative Cool with Customers BC Hydro , PowerSmart News Article
DTE Energy, 03/01/2012. Case Study: Save-A-Lot Food Stores DTE Energy, Energy Efficiency Program for Business
APS, 10/01/2014. Arizona Grocer Cuts Energy Use Solutions for Business Case Studies
Connecticut Energy Efficiency Fund, 10/01/2014. Case Study: Marandino Foods Connecticut Light and Power
Food Marketing Institute, 01/01/2013. Supermarket Facts: Industry Overview 2013 FMI