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. ceiling type refrigeration,
a single fan is mounted on the roof of the apparatus. This is suitable for small volume interiors, but is not used in larger refrigerators. Because it only has one location, it could allow for hot spots in the corners of the interior cabinet. In back wall or mullion 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, with air 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 resulting negative publicity 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 retention capacity the air contains at a given moment, expressed as a percentage. For example, 85 percent humidity indicates that the air contains 85 percent of the amount of water that it could contain 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 picks up moisture from the food, causing discoloration, cracking, and drying of the surface.
If the air has a 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 fungus or bacteria. Fortunately, most foods do well in 80 to 85 percent relative humidity. To achieve this optimum level, manufacturers are concerned 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 maintains humidity in the refrigerator cabinet. However, if the temperature of the coils gets too low, the moisture will turn into ice crystals and get stuck in the coils.
the reels
In this case, the airflow through the system is blocked and the moisture in the refrigerated space is depleted. As you can see, getting all the factors right is a delicate balance, with cost and food quality at stake. In short, it’s hard to keep coils frost free, but they need to be kept frost free for them to work properly. Adding heat to the defrost area of the coils can compromise the temperature of the food inside. A fairly new concept from Hussman Modular Defrost of Bridgeton, Missouri, it does exactly what it says on the tin: 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 chambers.
The idea works for entry and walk-in coolers, but not for freezers. Maintain food quality and save energy by keeping compressors from working overtime to make up 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 odors.
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 the produce 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, making the air in the freezer warm. The low humidity of freezers requires special food storage precautions. Use moisture and vapor proof packaging to prevent surface damage known as “freezer burn” if moisture condenses on the food.