The main function of the evaporator in a cold room is to absorb the heat from inside (air, goods, etc.), causing the liquid refrigerant within the coils to evaporate and turn into gas, which is then blown into the cold room for cooling.
When the evaporator coils operate at freezing temperatures and there is moisture in the air, frost accumulates on the coil surface. This frost negatively affects the cooling performance, both by obstructing air flow through the coils and reducing the heat transfer between the air and the refrigerant, thus decreasing the cooling capacity.
These impacts burden the refrigeration system, requiring more energy consumption. As the frost layer builds up, the demand for cooling increases because, although the refrigerant flow remains stable, the reduced capacity of the evaporator might warm the room. At this time you need to understand evaporator defrost.
Signs of Evaporator Coil Freezing
- The equipment operates but fails to cool your space
- Blowing warm air instead of cold
- Ice formation around the coils
- Thermostat temperature doesn’t match indoor temperature
- Ice and freezing on the lines near the outdoor unit
- Water accumulation near the drain pan
Evaporator Defrost Methods
Air Defrost
This method is the simplest, involving shutting off the refrigeration cycle and allowing air from the refrigerated space to pass over the evaporator coils, preventing refrigerant from entering the evaporator. Obviously, the air must be above freezing to work.
When ice buildup is severe, air defrost may also take a long time, and when unusually high accumulations occur, it can be difficult to remove the ice.
Electric Defrost
Electric defrost introduces an external heat source to melt the frost, for example, by inserting one or more electrical resistance heating rods along the length of the evaporator. While electric defrost is more common in low-temperature applications, it is also used in medium-temperature applications.
Electric defrost is more efficient and shorter in duration than air defrost. This solution is relatively easy to implement and cost-effective. This is because the purchase cost of electric heaters is quite low.
Hot Gas Defrost
Gas defrost uses the system’s internal energy to defrost the evaporator, utilizing naturally generated high-temperature exhaust steam to add the necessary heat for completing the defrost cycle.
The limitations and challenges of hot gas defrost appear in systems with a small number of evaporator coils. The energy used to generate the hot gas must come from somewhere, meaning some coils must remain in refrigeration to generate the hot gas used for defrosting.
Primarily used in large plants with multiple evaporators. Evaporators can operate while others are defrosting, thus alternating defrost.
Alternative Defrost Options
Water defrost and embedded glycol defrost are less common.
Water Defrost
As the name suggests, water defrost involves spraying water on the coil to melt the ice. These types of defrost systems are relatively common in spiral freezers and blast tunnels but can also be used in general freezer applications. They are very fast and have the added benefit of helping to keep coils clean.
Embedded Glycol Coil
Essentially, it involves a second set of tubes interlaced within the evaporator. Warm glycol is pumped into these coils to heat the coil and melt the ice. This has the same advantage as hot gas, in that the coil is heated from the inside out, thus faster than electric defrost. The coil volume is larger, increasing capital costs, but defrosting can utilize waste heat, thus reducing energy consumption.
Benefits of Evaporator Defrosting
- Keeps evaporator coils frost-free, allowing them to cool the inside of the cold room effectively;
- Maintains good airflow within the cold room, ensuring the air temperature throughout the interior is stable and uniform;
- Prevents frost from taking up valuable space within internal compartments;
- Prevents frost from causing damage to sensitive items or components.
- Reduces the burden on the refrigeration system, lowering energy consumption.
Considerations for Evaporator Defrosting
Intake temperature, relative humidity, air quality flow, and evaporator surface temperature are considered to have a strong influence on frost formation.
Initiate defrosting at specific intervals, provide defrosting only when necessary, and shorten the defrost cycle to only the required time. Up to 80% of total defrost energy costs can be saved.
The frequency and duration of defrosting depend on the stored product and its moisture content, as well as air exchange and humidity.
How often cold room doors are opened daily or people enter the room also affects cold room defrosting.
What Other Failures Can Occur in Evaporators?
Refrigerant Leak: Refrigerant leaks are a primary cause of evaporator failure. These leaks can occur due to corrosion, manufacturing defects, or accidental damage. When refrigerant levels drop, the evaporator can no longer efficiently perform its cooling function.
Aging and Wear: Like any mechanical part, evaporators wear out over time, reducing their efficiency. This wear eventually leads to failure.
If you have any questions about cold room evaporators, feel free to consult us. We have professional technicians and sales staff to answer your questions. Meanwhile, our cold room evaporator equipment is of very good quality and comes in various configurations to ensure optimal airflow and temperature consistency. Contact us for a quote.