Refrigeration Defrost Methods

Defrosting is essential in refrigeration systems to remove ice accumulation on evaporators, which reduces efficiency and cooling capacity.

Natural Defrosting

This method is typically used in refrigerated spaces operating above +2°C. It involves stopping the refrigeration system (compressor and fans) for a period, allowing the warmer ambient air within the refrigerated space to melt the ice accumulated on the evaporator.

In low-temperature facilities for freezing and storage of frozen products, based on forced-air evaporators, it becomes necessary to create additional heat for defrosting to melt the ice.

Water Spray Defrosting

This method involves spraying water under pressure onto the ice accumulated on the evaporator. The water melts the ice and cleans the evaporator.

The system should be designed so that all water projected onto the evaporator through showers or sprays is collected in a drain tray and the drain tube is capable of handling this flow.

Fan operation must be controlled; fans should be stopped from a few minutes before the water injection begins until a few minutes after it ends.

Defrosting by Brine

For very low evaporation temperatures (around -40°C), brine or an antifreeze solution should be used instead of water.

In this case, the return brine or solution is collected in a container for recovery and recycling. Unless the tank is large enough that reheating is not required, some means for reheating the solution in the tank may be necessary.

Since the water from melting ice will weaken the solution, the defrost system should be equipped with a system for concentrating the solution to return it to its original concentration.

Electric Defrost

Electrical resistors coupled to the evaporator, in intimate contact with the fins, heat the evaporator to completely melt the ice.

Potential issues with this method include:

• Heating the liquid phase refrigerant that may exist in the evaporator.
• The defrost resistors remaining energized after thawing, with the danger of overheating and damage.

To address the first issue (heating liquid refrigerant), a prior or simultaneous pump-down or system adjustment may be required. To address the second issue (resistors remaining energized), the installation of a thermostat or control switch is necessary to de-energize the resistors once defrost is complete.