Air circulation and humidity of the refrigerator
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 don’t want to do anything to block the airflow. There are three basic types of forced air systems in refrigerators. roof type cooling,
a single fan is mounted on the ceiling of the apparatus. This is suitable for small volume interiors, but is not used in larger refrigerators. Since it only has one location, it could allow hot spots in the corners of the interior cabinet. In back wall or mullion type cooling, the airflow system draws 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 the air is circulated through a series of small vented air ducts to various points on the back wall of the cabinet. How important is air circulation? Well, the difference between safe and unsafe raw foods can be as little as five to seven degrees Fahrenheit. Seafood, poultry, or red meat will spoil in 18 to 24 hours if the refrigeration temperature exceeds 42 to 45 degrees.
Fahrenheit, and you already know the HACCP guideline of temperatures no higher than 40 degrees Fahrenheit. Would you rather risk a lawsuit and the negative publicity resulting from food poisoning allegations, or would you rather keep the air in your refrigerator circulating properly?
Humidity is the amount of moisture (or water vapor) in the air. At different temperatures, air can contain different amounts of water. In refrigeration, the type of humidity we are interested in is relative humidity, or how much of its maximum water-holding capacity 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 hold at that temperature. Relative humidity greatly affects the appearance and rate of spoilage of many foods. If the air surrounding stored food has a very low relative humidity, for example, the air naturally absorbs moisture from the food, causing discoloration, cracking, and surface drying.
If the air has a high relative humidity, some of the moisture will condense on foods that are supposed to stay dry, causing them to soften or grow mold or bacteria. Fortunately, most foods do well in 80 to 85 percent relative humidity. To achieve this optimum level, manufacturers make sure that refrigerator evaporator coils are large enough to operate at a temperature a few degrees lower than the desired temperature of the appliance. This differential reduces the amount of moisture that collects on the evaporator coils and keeps moisture in the refrigerator cabinet. However, if the temperature of the coils drops too low, the moisture will turn into ice crystals and get stuck in
the reels
In this case, airflow through the system is blocked and moisture is depleted in the refrigerated space. As you can see, getting all the factors right is a delicate balance, with costs and food quality at stake. In short, it is difficult to keep coils frost free, but it is necessary to keep them frost free 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 its name implies: 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 cameras.
The idea works for walk-in and walk-in refrigerators, but not for freezers. Maintains food quality and saves energy by keeping 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 sorbit to absorb moisture and odours.
We mentioned that most foods do well at 80 to 85 percent relative humidity, 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 most refrigerators have separate, closed produce bins to retain the natural moisture of vegetables and restrict airflow.
Freezers maintain an average relative humidity of only 30 to 35 percent. 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. The low humidity of freezers requires special food storage precautions. Use moisture- and vapor-proof wrapping to prevent surface damage known as “freezer burn” if moisture condenses on the food.