Hot gas defrost
① The high-temperature and high-pressure gas coming from the compressor is put directly into the evaporator to heat up the evaporator coil to defrost.
– Large devices: Defrost with the latent heat of condensation (gas-liquid separation with the liquid separator at the evaporator outlet )
– Small devices: Defrost by sensible heat of hot gas (no phase change)
– No need to install an electric heater.
– Water piping is not required.
– Defrosting is difficult to perform if the frost is too thick.
① Spray water on the evaporator coil to defrost.
– Recover the refrigerant in the evaporator, stop the fan and spray the water at the temperature of 10 ℃ to 20 ℃ on it.
– For this, the air outlet of the evaporator should be blocked.
– The most simple and standard method, and is widely used in unit cooler etc.
– Defrosting is available within a short period of time if applied with a high volume of water.
– Water piping equipment required.
– Freeze prevention measures required for water supply pipes.
– Freezing of water may cause the fan to be stopped.
– There is a concern of possible splash of water on the coil when the fan starts to blow again after defrosting.
– It is common to put the water to use in a tank (water tank for defrosting) and raise it to a certain temperature and recirculate it.
① Install an electric heater at the proper position of the evaporator to defrost.
– Stop the fan and heat it when defrosting.
– Heater capacity is about 5kW per 1RT.
– Mainly used on small devices. In case of a large device, there is a problem with the manufacturing of a heater and repair for failure.
– Easy to operate and control an electric heater.
– It is possible to reduce heating unevenness by properly setting the heater installation method.
– There is a need to install a circuit breaker, thermostat, etc. in the heater to beware of fire.
– There is a need to replace an electric heater after a certain period of use (heater becomes old after use).
Defrosting by antifreeze spray
① Method to prevent frosting by spraying antifreeze (brine) on the cooling pipe continuously.
– The frost is absorbed into the antifreeze as soon as it is formed, so the heat transfer surface always remains free from frost.
– Regenerate by heating the antifreeze with decreased concentration.
– There is no increase in the internal temperature caused by defrosting (because there is no need to stop the operation for defrosting).
– The heat transfer rate of the cooling pipe is large due to the wet surface effect on the non-frost and heat transfer surface. Therefore, the heat transfer surface can be made small (since the K value is good).
– Expensive equipment cost (due to the use of regenerative anti-corrosive materials).
– Antifreeze should be selected in consideration of hygiene of stored products inside (to prevent damage to refrigerated products).
– Antifreeze which has high humidity at low temperature should be avoided.
– There is a method of spraying antifreeze at all times or spraying it only in the case of defrosting.