The refrigerator relies on forced air to transfer heat. The fans inside the appliance move the air. The faster the air flows, the faster the heat is removed. For this reason, you do not want to do anything to block the air flow. There are three basic types of forced air systems in refrigerators. In ceiling type cooling,
a single fan is mounted on the ceiling of the appliance. This is suitable for small volume interiors, but is not used in larger refrigerators. Because it only has one location, it can allow for hot spots in the corners of the interior cabinet. In rear wall or mullion type refrigeration, the airflow system takes in air above the top shelf and discharges it below the bottom shelf.
The duct type refrigeration system is a combination of the first two types. Here, the forced air unit is located at or above ceiling level, and air circulates through a series of small vented air ducts at various points on the rear wall of the cabinet. How important is air circulation? Well, the difference between safe and unsafe raw foods can be five to seven degrees Fahrenheit. Seafood, poultry, or red meat spoils within 18 to 24 hours if its refrigerated temperature exceeds 42 to 45 degrees.
Fahrenheit, and you already know the HACCP guideline for temperatures no higher than 40 degrees Fahrenheit. Would you rather risk a lawsuit and negative publicity resulting from food poisoning allegations, or keep the air in your refrigerator circulating properly?
Humidity is the amount of moisture (or water vapor) in the air. At different temperatures, the air can contain different amounts of water. In refrigeration, the type of humidity that interests us is relative humidity, or the amount of its maximum water-holding capacity that the air contains at any given time, expressed as a percentage. For example, 85 percent humidity indicates that the air contains 85 percent of the amount of water it could contain at that temperature. Relative humidity greatly affects the appearance and spoilage rate of many foods. If the air around stored food has very low relative humidity, for example, the air naturally picks up moisture from the food itself, causing discoloration, cracking and drying of the surface.
If the air has high relative humidity, some of the moisture will condense on the food that is supposed to be kept dry, causing it to soften or grow mold or bacteria. Fortunately, most foods do well in relative humidity of 80 to 85 percent. To achieve this optimum level, manufacturers are concerned that the refrigerator’s evaporator coils are large enough to operate at a temperature a few degrees lower than the desired appliance temperature. This differential reduces the amount of moisture that builds up on the evaporator coils and instead keeps moisture in the refrigerator cabinet. However, if the temperature of the coils is too low, the moisture will turn to ice crystals and get stuck.
the reels.
In this case, the air flow through the system is blocked and the humidity in the refrigerated space is depleted. As you can see, having all the right factors is a delicate balance, with food costs and food quality at stake. In short, it is difficult to avoid frost on the coils, but it is necessary to keep them frost-free in order for them to function properly. Adding heat to the area, to defrost the coils, can compromise the temperature of the food inside. A fairly new concept from Hussman Modular Defrost of Bridgeton, Missouri, does exactly what the name suggests – it defrosts the coil in sections. The automated system defrosts coils in no more than nine minutes per section and never defrosts adjacent sections at the same time, all programmed by an electronic controller capable of running up to six walk-ins.
The idea works for handheld and take-out refrigerators, but not freezers. Maintains food quality and saves energy by preventing compressors from working overtime to compensate for frozen coils. Humitech International Group, Inc. of Dallas, Texas, pioneered another humidity control suggestion for indoor refrigerated spaces. Humitech uses a mineral product called sorbitol to absorb moisture and odors.
We mentioned that most foods do well in relative humidity of 80 to 85 percent, but fresh fruits and vegetables are exceptions. They require more humidity, up to 95 percent. To increase the moisture content, you can slow down the air circulation. This explains why there are separate closed fruit and vegetable containers in most refrigerators to retain the natural moisture in the vegetables and restrict air flow.
Freezers maintain an average relative humidity of only 30 to 35 percent. Any more moisture would automatically raise the temperature because it would hit the coils, freeze in place, and block airflow, causing the air in the freezer to heat up. Low humidity in freezers requires special precautions for food storage. Use moisture and vapor proof packaging to prevent surface damage known as “freeze burns” if moisture condenses on food.
