The big cover-up in the refrigeration case

April 10, 2000
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It is estimated that 75% of the supermarkets in North America are closed to the public for 6 to 8 hrs at night. With little effort, these supermarkets could claim dollars that are lost during the stores’ closed hours from unnecessary energy consumption and premature spoilage of many perishable products.

Open refrigerated display cases are the best way for retailers to present fresh merchandise to consumers. Unfortunately, these cases are also open to the effects of heat and UV radiation from the store environment.

Heat that travels and its effects

There is often a misconception that the refrigerated air escapes from the display case. However, heat or warm air is actually drawn toward the colder air, raising the temperatures in the display case; this causes merchandise to warm up and compressors to operate more frequently.

The warming of the refrigerated air at the surface of the display case causes a difference in temperature between the first foot and the back of the display shelves. Most consumers have occasionally noticed food products that are warmer at the front of the case than those deeper into the case. The placement of thermometers at the front and rear of open refrigerated display case shelves easily confirm this.

A refrigerated case full of products will show greater differences in temperature than an empty display case. Cold air does not flow as freely when blocked by stacks of merchandise within the case.

In addition, the merchandise itself will hold the temperature of its surroundings, helping to keep the colder rear areas cold and the warmer, more exposed open surfaces warm.

More frequent compressor operation and exposed products must be tolerated so that consumers can shop freely, but when the store is closed, simple steps can be taken to reduce store energy consumption and extend product shelf life with ideal cold temperatures.

Creating a barrier at night

To solve this problem, an efficient temperature barrier is needed between the opening of the display case and the store interior. The ideal thermal barrier arrangement must have several qualities to be effective in increasing store profit:
  • Reasonable cost and quick initial payback period;
  • Simple and quick to put in operation;
  • No interference with customer access to fresh merchandise when the store is open;
  • No disturbance to the cosmetic appearance of the store;
  • Durable commercial quality;
  • Hygienic (will not rust or attract dust, mold, and mildew);
  • Simple, quick cleaning maintenance that can be done when cleaning the case; and
  • Effective in the reflection of heat and UV radiation.

Some methods of closing cases have included plastic strip curtains and solid plastic curtains.

Wildly escalating energy costs in Europe led to the development of another type of material that can be used in open refrigerated display cases in supermarkets. Engineers and display case manufacturers provided consultation to conclude that reflective aluminum prevented 70% of the heat gain at the opening of a refrigerated case.

Placing sheets of aluminum over open cases during closed hours was obviously not practical due to storage and handling problems. A vertical rolling curtain permanently attached to the top of the display was agreed upon as the simplest and easiest to use arrangement.

To adapt to this arrangement, a 99% pure aluminum heat-reflective fabric was developed. To provide strength to the woven aluminum fabric and eliminate oxidation, it is coated with a thin, transparent film.

Humidity levels in a store are often very high compared to the level inside a display case, and condensation can form due to the temperature differences between the inner and outer fabric surfaces. To allow the woven aluminum fabric to breathe and condensation to evaporate, it is punched with a precise pattern of tiny holes. The perforations represent 1.5% of the total heat-reflective surface area.

The fabric is placed on a rustproof, spring-loaded spindle that is mounted in an aluminum enclosure for adaptability in regard to the retrofit of existing display cases. The assembly includes a nylon handle, hook, and mounting end caps that are durable, cost effective, and cannot rust.

Payback

Even in areas that have low energy costs, supermarkets report their energy bills to be approximately 1% of their total sales volume. However, profit margins within the supermarket industry are very low, also around 1%. Any improvement in reducing costs helps make substantial improvements to profit.

Several factors affect the payback on investment for the purchase of woven aluminum night covers:

  • Hours the store is closed;
  • Local energy cost;
  • Number of cases;
  • Types of cases;
  • Equipment efficiency;
  • Heat sensitivity of perishable merchandise; and
  • The store environment.

Retailers with a minimum 60 hrs closing time per week that use aluminum night covers have reported a payback in as short as three months to as long as 20 months.

The payback is derived from reduced energy costs through less frequent compressor operation and maintenance, as well as reduced store heating or air conditioning operation.

However, retailers have reported that the quickest payback is from the protection of all heat-sensitive merchandise from exposure to heat and UV radiation during closed hours. Protection from heat and UV radiation is particularly important in the fresh meat and produce departments. This sensitive merchandise tends to dry, wilt, and discolor from exposure to heat and dry air within the store.

Produce cases

At the end of the day, produce departments usually restock the display cases with new merchandise. Older produce is rotated to the top of the display case.

If a case is filled to capacity, the refrigerated air has difficulty effectively cooling all of the produce surface area, leaving it vulnerable to heat and UV. Even with automatic sprayers to moisten the produce during the closed hours, there is still plenty of spoilage to trim away before store opening each morning.

Most supermarkets report significant shrinkage on produce displayed at the front portion of their cases, which is not well reached by the cold air and spray.

Woven aluminum night covers reflect heat and UV away, creating the optimum temperature and humidity around all the produce held in the case. This can eliminate morning produce trimming, which can save roughly $1 of produce/ft of case plus associated labor. A supermarket with 100 or 200 ft of produce display receives quick payback from product sold that would normally be accepted as a daily loss.

Meat cases

Meat products, when exposed to heat and UV, create photochemical reactions on the surface of the cuts that lead to color change.

For example, meat and sausage cuts fade considerably or go gray, thus losing their fresh appearance. Severe discoloration can also catalyze liquid oxidation, which results in deterioration of the meat’s aroma and flavor.

Strict control of temperature and minimizing the time at warmer temperatures are critical to solving color fading and prolonging shelf life of fresh meat products.

Floral cases

Retailers report that floral cases closed with glass doors provide for longer shelf life, but floral sales are much better when using an open case. Woven aluminum night covers offer open merchandising when the store is open and prolong shelf life when the store is closed.

For more information, contact the Econofrost Div. of MGV Inc., P.O. Box 40, Shawnigan Lake, BC VOR 2W0, Canada; 800-519-1222; 250-743-1221 (fax); econofrost@mgvinc.com (e-mail); www.mgvinc.com/econofrost (Web site).

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