What defrost methods are used for CO2 unit coolers?

Common defrost methods used for CO2 unit coolers are:

1. Electric defrost
Electric heaters are installed in or around the coil and drain pan. During defrost, the heaters melt frost and ice from the coil surface. This is a common option for low-temperature cold rooms and freezer rooms because it is simple to control and does not require hot refrigerant gas piping.

2. Hot gas defrost
Hot gas defrost uses high-temperature refrigerant gas from the system to warm the evaporator coil and melt frost. In CO2 refrigeration systems, this method is often used in industrial and commercial low-temperature applications because it can provide fast and effective defrost when the system is designed correctly.

3. Off-cycle defrost
Off-cycle defrost is mainly used in medium-temperature cold rooms, not deep freezer applications. The refrigerant flow stops while room air continues to circulate over the coil, allowing frost to melt naturally. This method is only suitable when frost buildup is light and room temperature is high enough to support defrosting.

4. Water defrost
In some special applications, water can be used to melt frost from the coil. This is less common for CO2 unit coolers than electric or hot gas defrost, but it may be considered in certain industrial environments where hygiene and fast frost removal are important.

Which method is best?

The best defrost method depends on:

• room temperature

• humidity level

• frost load

• system design

• energy considerations

• maintenance preference

For freezer rooms, electric defrost and hot gas defrost are the most common choices.
For chiller rooms, off-cycle defrost may be enough in some cases.