Commercial refrigeration offers defrost features as a convenient way to keep your system operating properly. Ice accumulation occurs on evaporator coils when the fridge reaches temperatures below 40°F. For your refrigeration to remain reliable and energy-efficient you need to remove excess ice build-up on a regular basis.
Regardless of what type of commercial refrigeration you need, from display cases to mobile refrigeration, the good news is defrost options reduce icy build-up. There are 2 defrost methods available: 1) Electric and 2) Hot Air. Both are quite effective at keeping your freezer ice-free. Here are how the two different methods work and the pros and cons of each.
Electric defrost systems use electrical heating elements installed along or directly in the fridge’s evaporator coils. When the defrost cycle kicks in, a solenoid valve stops refrigerant from flowing to the evaporator. It then energizes the heating elements, and the evaporator uses its fans to blow hot air over the coils. This melts the ice.
Hot Air Defrost
For hot air there are actually 3 possible methods used. While all use high-temperature refrigerant vapor discharged from the compressor for heat, there are a few ways this might occur:
1. The three-pipe system
These refrigerators come with a third pipe, or “defrost line” connected to a solenoid valve which remains closed during the refrigeration cycle. When closed, refrigerant can travel through the system. However, when in defrost mode, the solenoid valve is activated allowing high-pressure, high-temperature refrigerant vapor to go through the defrost line. It bypasses the expansion valve and condenser and travels through the evaporator’s inlet which warms and melts the ice.
2. Reverse cycle
In this case, a four-way reversing valve is used to direct the superheated refrigerant vapor through the evaporator coil backwards, hence the name. When this happens the ice melts and condenses the refrigerant vapor into liquid allowing it to pass through an expansion valve where it re-vaporizes. When it travels backwards through the condenser, it returns to a low-pressure vapor to the compressor suction.
3. Reverse flow
An existing suction line reverts the flow of the hot refrigerant vapor to the evaporator in this method. The discharge line pipes the hot refrigerant vapor to the evaporator through a defrost header and solenoid valve. Once it exits the evaporator, the refrigerant flows through the liquid line valve to the liquid header.
All three methods are effective ways of defrosting ice buildup.
Pros and Cons of Electric and Hot Air Defrost
Here are a few things to consider when deciding what method is best for your needs:
Hot gas systems require pipe installation so tend to be more complicated for installation.
The electric defrost uses more energy trying to disperse the heat. Also, humidity inside the refrigerator tends to be higher during the process because it’s possible for the heating elements to be partially covered in ice during the process and the ice turns to vapor.
This may be bad as it can encourage bacterial & fungal growth but also may cause the coils to freeze once the next refrigeration cycle kicks in. It is important to set the electric defrost cycles carefully and they will be very effective. The gas defrost method on the other hand uses latent existing gas to heat the coils which take up less energy. It also creates less moisture.
Defrost Cycle Duration
It takes some time for the electric heating elements to heat up which can add a little more time to the cycle duration. As well, as mentioned, the electric method isn’t as efficient, so does take longer to complete the defrost cycle. Because of this, the inside compartment can also heat up more which can pose an issue as you might need to wait before you can put food back into the compartment safely.
Hot gas defrost cycles use hot vapor already in the system, so there is no waiting period for anything to heat up. Because of this and the fact it is more efficient overall, the cycle tends to be much shorter. This reduces the risk for temperature variations in the compartment as well.
While both hot air and electric defrost methods do the job of keeping ice build-up at bay, overall the hot air system tends to be more reliable. It uses up less energy and takes less time to complete the defrost cycle. You’ll have to keep the installation process in mind since it requires more components in the process, but in the long run, you’ll find it still outshines the electric defrost method.
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