Commercial Freezer Defrost Cycles Explained

A freezer's defrost cycle is something most of us rarely have to think about. Gone are the days when we needed to manually defrost our equipment to keep it running smoothly. That goes for equipment in our homes and our restaurant freezers alike. Although we don't have to deal with them, defrost cycles didn't go away - the process is just taken care of automatically for us. When you see your equipment's defrost light come on, you may ask yourself: What's the purpose of a freezer defrost cycle, and does it have any effect on the food inside the equipment?

Why Do Freezers Have Defrost Cycles?

For most applications, the ideal freezer temperature range is from -10 to 10 degrees Fahrenheit, where food is kept well below freezing and its safety and texture are maintained. The component responsible for removing heat from the refrigerator cabinet to create those cold temperatures is the evaporator. It goes without saying that this component gets cold, sometimes several degrees colder even than the air inside the freezer.

Anyone who's been inside one knows that commercial kitchens can be humid places, since cooking and the process of cleaning dishes tend to generate a lot of steam. When some of that moisture inevitably finds its way into your freezer, it condenses into water. When that condensation happens on the freezer's evaporator coils, it turns into frost.

Left unchecked, that frost will develop into a layer of ice that can affect the performance of the equipment by preventing the evaporator coil from absorbing heat and cooling the cabinet. A frosty evaporator runs the risk of letting freezer temperatures become dangerously warm. Extreme levels of frost will put a burden on the refrigeration system that it can't overcome, causing it to fail. Defrost cycles are designed to avoid problems caused by the buildup of ice.

How Do Defrost Systems Work?

A defrost system does its work in one of two ways. Just about every modern commercial freezer is built with a heating element attached to its evaporator coil. When the defrost cycle is initiated, this coil is energized to melt away the frost that has formed there.

Hot gas condensate systems have been in use a bit longer and are used by several manufacturers, including Turbo Air. This method temporarily reverses the equipment's refrigeration cycle, so instead of drawing in heat, the unit's evaporator coil releases heat to melt ice that has gathered on it. That temporary warmth also helps promote evaporation of the melted condensation, helping to prevent its promoting corrosion on surrounding metal components.

Defrost systems are almost always "time initiated," meaning an internal timer will start the cycle on a set interval regardless of the actual conditions inside the equipment. In traditional equipment, this timer ran constantly. Timers on modern equipment only advance when the freezer's compressor is running, a design that's intended to save energy.

A freezer's defrost cycle terminates in one of two ways. In some equipment, the cycle terminates the same way it was initialized - according to a timer. This method gets the job done, but isn't always efficient because the length of the cycle has nothing to do with whether the evaporator is actually defrosted. That can mean the cycle runs for too long or not long enough.

The second way of terminating a freezer defrost cycle is more accurate. It involves measuring the temperature of the evaporator to decide when to resume normal operation. This method saves energy because it can accurately predict when all the ice has been removed from the evaporator and avoid running the defrost cycle longer than necessary.

By now you may be wondering what happens to the water created when a freezer defrost system melts the ice. It's usually piped into a tray underneath the unit where it may be heated so it evaporates more readily. Manufacturers sometimes include wicking systems that cause the water to evaporate without the need for any electrical components.

Does a Defrost Cycle Affect the Food in the Freezer?

Since the cycle involves producing heat, many operators wonder if their food is in any danger of reaching unsafe temperatures when their equipment defrosts. Rest assured the manufacturers take into account food safety when they design their equipment. Defrost systems are designed to produce just enough heat to melt the ice that has gathered on the evaporator coil. The cycle doesn't last long enough to affect the interior temperature of the cabinet, much less the food held there.