Both household refrigerators and large industrial and commercial cooling systems need to periodically eliminate the ice buildup on evaporators. Without proper defrosting in refrigeration systems, the heat transfer efficiency in evaporators is drastically reduced. As a result, cold storage rooms may not achieve the required temperatures, which can range from -10 to -40 °C.
Where does the accumulated ice on evaporators come from?
It is common for people unfamiliar with industrial refrigeration systems to ask this question. The ice that accumulates on evaporators comes from the relative humidity of the air circulating inside the cold storage room. This humidity, in turn, comes from the external environment when the doors of the cold storage room are opened, and from the objects contained in it.
Over time, the accumulated ice prevents air from passing through the finned coil of the evaporator. Consequently, the direct contact of the air with the metallic surface of the evaporator tubes is lost, hindering heat transfer. Therefore, it becomes essential to schedule defrosting in refrigeration systems to maintain cooling efficiency.
Energy efficiency and defrosting in refrigeration systems
Due to high energy costs and strict environmental regulations, it is important to keep refrigeration systems operating at maximum efficiency. If defrosting in refrigeration systems works correctly, evaporators will achieve more effective heat transfer.
Therefore, less energy will be needed to maintain the temperature inside the cold storage room. Consequently, industrial refrigeration systems will make better use of consumed energy, increasing energy efficiency.
Methods for defrosting in refrigeration systems
There are four methods for defrosting in refrigeration systems: manual, start-stop cycle, electric resistances, and hot gas. Each of these methods has its advantages and disadvantages, depending on the system conditions and construction. Below, we explain each of them:
Manual defrosting method in cold storage rooms
The manual defrosting method is performed directly by a technician using a spatula to remove the accumulated ice. This procedure must be carried out with the system turned off and very carefully to avoid damaging the tubes and fins of the evaporator coil.
One disadvantage of this method is that the technician has to enter the cold storage rooms where the evaporators are located to remove all the ice. This work is feasible depending on the physical location of each evaporator and the ease of dismantling the structure covering the coil.
In many cases, this manual defrosting method is only applicable as an emergency measure or on special occasions. This is because this procedure requires a lot of time and the use of trained personnel.
Start-stop cycle defrosting method for industrial refrigeration systems
Depending on the conditions, the start-stop cycle method is sufficient to prevent the progressive accumulation of ice. The implementation of this method is done with electronic timer relays, which perform an automatic start-stop cycle at certain intervals.
The adjustment of the time between each cycle and the duration of the stop is the responsibility of the technicians or system operators. These individuals have the knowledge and experience to optimize these times.
One of the great advantages of the start-stop cycle defrosting method is that it only requires electronic timer relays. These devices have a relatively low cost and are easy to install.
Hot refrigerant gas defrosting method
The hot refrigerant gas defrosting method uses a small portion of hot gas, at the compressor outlet of the refrigeration system. This hot refrigerant gas is conveyed through pipes to the inside of the coil tubes after the cold refrigerant has been evacuated.
This way, all the ice can be removed from the evaporators in a very short time and with maximum efficiency. However, defrosting in refrigeration systems with the hot gas method is technically very expensive and complex.
One advantage of the hot refrigerant gas defrosting method is that it harnesses the system’s own thermal energy. Consequently, this method has high energy efficiency and does not depend on external energy supply.
Electric resistance defrosting method
The electric resistance defrosting method is currently the most widely used, both in household refrigerators and large industrial systems. This is due to the great versatility and high efficiency of this method. Defrosting in refrigeration systems with electric resistances works automatically, thanks to the heat emitted by the resistances when supplied with electrical energy. This procedure is performed after a pump-down maneuver to evacuate the cold refrigerant from the evaporators.
To implement this method of defrosting with electric resistances, electronic timer relays and thermostats are used in addition to the resistances. In a way, this method is an extension of the start-stop cycle mentioned earlier. However, the resistance method is more versatile, effective, and fast, but it is more expensive because the evaporators must be designed to accommodate resistances.
Intersam, a specialist company in heat exchangers for refrigeration systems
Intersam’s evaporators (heat exchangers) are designed and manufactured to use both the hot refrigerant gas defrost method and the electric resistance defrost method. In this way, at Intersam, we guarantee efficient defrosting in commercial and industrial refrigeration systems. The resistances of our evaporators are protected against electrical insulation faults and have a long service life. Furthermore, our evaporators are robust, corrosion-resistant, and designed to quickly remove all collected liquid water.