A build up of ice around the evaporator makes it much harder for the refrigerator to work efficiently, as water and ice may leak into internal components of the refrigerator. It also makes it harder for the evaporator to absorb and transfer heat, resulting in a gradual increase of internal temperatures, eventually making your refrigerator less effective.
A build up of ice can also cause freezer burn to your stock, and limits airflow around the unit. And reduced airflow means your fridge has to work twice as hard to cool your stock.
This is why making sure your commercial refrigerator goes through a regular defrost cycle is key to keeping your appliance working smoothly.
So you know that defrosting the evaporator is important, and you know that it needs to happen regularly. But how does a commercial refrigeration defrost system actually work? There are 3 common defrost methods used in commercial refrigeration:
In some older commercial and domestic freezers, it may be necessary to manually switch off the appliance and remove any ice build up yourself.
Avoid using any hard or sharp objects such as a knife, hammer, chisel, or screw driver to chip away at the ice. This can seriously damage the interior of your refrigerator, potentially nicking the coil and causing the refrigerant to leak.
It’s always better to switch off the appliance, remove the products inside, and allow the ice to melt away naturally, or with the help of some water. You can also use a heat gun to speed up the process of the ice melting, but you run the risk of damaging any plastic components inside the fridge if you get too carried away. A torch or flame is not recommended as it’s more difficult to control the heat output. We go into detail about manually defrosting your refrigerator and other potential problems your commercial fridge may face here.
As there is no built in defrosting system in certain models, you’ll have to create a schedule for yourself to regularly remove the ice build up. You can also set a timer so that the fridge or freezer turns off by itself to allow the ice to melt away on a regular timed schedule.
Off cycle defrost systems are the most common defrosting systems found in commercial kitchen and catering refrigerators, such as those you see in restaurants, bars, and shopping centres. Off cycle systems are only appropriate for medium temperature fridges that don’t go below 1 degree Celcius.
The basic function of this system is the temperature controls dictate when the compressor cycle can begin again after the defrost cycle has occurred. Once the evaporator coil temperature has increased and it’s finished defrosting, this will signal the compressor cycle to start cooling the unit again.
So as the name suggests, defrosting occurs in the off cycle, when the refrigerator components have stopped cooling the unit down further. The refrigerator will not cycle back on until the evaporator has increased in temperature and completely defrosted.
There are two different types of controllers, temperature and pressure controllers, which are used to monitor the temperature of the evaporator coils. These controls must be set at the correct value to ensure that the evaporator coils fully defrost before the unit starts the cooling cycle again.
The temperature controller for an off cycle defrost system is referred to as a constant cut-in controller. This controller is specifically designed to monitor the temperature of the evaporator coil.
The cut-out value, or the point at which the cooling cycle will shut off and defrosting will begin, is usually at about 1 degree Celcius. The cut-in value, or the point at which the cooling system will cycle on again, is usually set to about 4 degrees Celcius. These temperature values are set according to the manufacturer of your particular refrigerator model.
A pressure controller is quite similar to a temperature controller, but rather than controlling the defrost cycle through temperature of the coil, it’s controlled via pressure of the refrigerant.
The temperature of the evaporator is still being monitored, and it still relates to the temperature of the case. However, the pressure of the refrigerant is being measured and controlled. This pressure indicates the temperature of the evaporator coil.
Pressure controllers have two settings:
Cut-in pressure setting: ensures the pressure of the refrigerant is equal to the maximum temperature of the evaporator coil, causing the unit to cycle on again after defrosting.
Differential pressure setting: determines the cut-out point, or the point at which the unit cycles off to allow for defrosting.
For refrigerators that run on cooler temperatures below 0 degrees Celcius, such as freezers, walk in freezers, and reach in freezers, simply shutting off the cooling cycle will not be enough to quickly defrost the evaporator coil.
Extra heat will need to be applied to the evaporator coil at regular intervals to keep it from freezing over. Electric heat is the most popular form of supplementary heating, while hot gas or vapour is used in larger refrigeration systems.
In electric heating, the heating element is attach to, or embedded into the evaporator coil itself so that it can apply heat directly, quickly melting off any ice build up, and turning off to allow the cooling process to start up again.
Electric supplemental heating systems rely on a timer to determine when a defrost cycle should be initiated. When the defrost cycle begins, a solenoid valve blocks the coolant from flowing into the evaporator, and the heating element powers on, melting all the ice build up. Then a timer, pressure sensor, or temperature sensor on the coil determines at which point the defrost cycle shuts off and the cooling cycle begins.
Defrosting your evaporator is a necessary aspect to maintaining your fridge, it can’t be avoided. The defrost cycle is a delicate balance between keeping your evaporator clear of frost build up, but also not defrosting too regularly. The evaporator likely doesn’t need defrosting every 5 minutes, for example.
If you’re removing ice manually, then use your own judgement to determine how long it takes for the ice to start building up, and how regularly you wish to remove it.
In most other commercial refrigerators with automatic defrost, the temperature controls, pressure controls, or timer controls will determine how often the unit needs to defrost, anywhere from every 2 hours to once a day or more, allowing you to adjust if needed. If you’re looking for a commercial refrigerator with a high quality automatic defrost system, check out our range here.
