Defrost is one of the important issues in cold storage rooms and we are going to talk about different kinds of it in this article. Evaporators are used in all cold rooms and freezers all around the world to adjust the temperature of the room. But do you know what happens that ice is accumulated on evaporator coils?
How is frost developed in cold room refrigeration systems?
People, products and equipment entering and exiting the cold storage rooms, let the ambient air into the room too. So, the temperature goes up and should be regulated back down again. This ambient air contains larger amount of moisture and water vapour than the air inside the cold room.
On the other hand, the refrigerant flowing inside the evaporator is always colder than the cold room air. This temperature difference causes Frost build-up on the evaporator and limits the air flow around the coils. So, the evaporator efficiency reduces which can also hurt the Compressor.
This ice and frost should be rapidly and effectively removed to restore the refrigerant productivity. There are different defrost methods, each have their own advantages and disadvantages. Here, we are going to talk about 4 most common and effective methods.
Defrost methods in cold room refrigeration system
Refrigeration defrost in off-cycle method
This is the simplest and least expensive defrost method which is appropriate for cold rooms operating above 2°C. The ice and frost is melted by periodic turning off the refrigeration system while the cold room air flow is maintained in the cold room. The cold room air melts the ice and the water is filled in an especial tray to leave the room. The number of refrigeration system's off-cycle and its length depend on the ice thickness on the evaporator.
Note: the room temperature goes up some degrees in this defrost method. So, special considerations should be given to the products to keep their quality.
Advantages:
- Being so cheap and simple
Disadvantages:
- Low control on cold room temperature
- Not being suitable for all cold storage rooms.
- Risk of defrost water reaching products.
Refrigeration defrost in electric method
This is one of the most common refrigeration defrost methods. The electric elements are placed between the evaporator coils to melt the ice and frost accumulated on them.
Note: this method is usually applied in cold rooms for which the off-cycle method is inappropriate.
During the defrost cycle, fans are off and the elements are turned on. Refrigeration system controllers use defrost timers and digital thermostat to control the number, temperature and duration of the cycle in a day.
Tip: using digital thermostat is the best way for melting the ice in the defrost electric method.
Advantages:
- High speed
- Not being so complicated
- Good control on the defrost cycle
- Being appropriate for all kinds of cold rooms, no matter big or small.
Disadvantages:
- Medium insulation cost
- High energy cost
Refrigeration defrost in hot gas method
Refrigerant is used in this method to melt the ice and frost on evaporator coils. The hot gas method can be used both in big or small cold rooms. In this method, fans are stopped and part of the hot discharge vapour from the compressor outlet is diverted directly to the evaporator to raise its temperature. So, the evaporator coils are heated from inside, melting all the ice and frost on the surface.
Advantages:
- High speed
- Good control on the operation
- Being appropriate for all kinds of cold rooms
- Lower energy cost
Disadvantages:
- High installation cost
Refrigeration defrost in reverse cycle
Reverse cycle defrost system is mostly used in smaller cold rooms. The direction of refrigerant flow is reversed in this method. As a result, the evaporator functions as a condenser and the condenser turns into an evaporator. So, the hot gas passes through the evaporator and melts the ice and the frost. The fans are also switched off in this method. So, heat is maintained inside the system to melt the ice.
Advantages:
- High speed
- Good control on the defrost operation
- Being appropriate for small cold rooms
- Lower energy cost
Disadvantages:
- Moderate installation cost
- High complexity
There are also other defrost methods for refrigeration systems of cold rooms but the four methods we mentioned here are the most common ones. If you need more information about refrigeration systems of cold rooms and chillers, don't miss refrigeration training course in HelloTechnic website. Our experts will teach you all the information you need about cold room and chiller refrigeration systems.
