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Evaporator Coil Air Conditioners - the evaporator in air conditioners is responsible for absorbing heat into the coils and the refrigerant. The evaporator in heat pumps and air conditioners is an essential component of vapor compression refrigeration. This is usually done as a result of passing air or water over the evaporator coil where a heat exchange process takes place.
Heat leaves the air or water (whatever medium is used) and is absorbed into the coil and the liquid refrigerant. As more and more heat is absorbed by the evaporator coil and the refrigerant again changes state from a liquid to a refrigerant vapor. By the time the refrigerant leaves the evaporator coil the refrigerant should be all vapor and ready to be received again by the refrigeration compressor.
Evaporator Coil Air Conditioners - Refrigerant Flow & Types
The evaporator is typically inside the air handling unit or it can be installed in the ductwork near the air handling unit. When the air handler blower turns on and the condenser is running refrigerant flows from the compressor through the condenser and then through the metering device and into the evaporator. Evaporators used in residential and light commercial HVAC can be classified as finned evaporators.
Coil Types | Evaporator Coil Air Conditioners
There are other types of evaporators used for various applications but finned evaporators are used extensively for HVAC. Various types of evaporator coils used for heat pumps and air conditioners include:
- “A” coils. These are typically in the shape of an “A”. See the photo below for an example of an A-coil evaporator.
- Slab coils - A slab coil is simply one solid piece of the coil. It looks similar to a radiator in your car.
- N-Coil - Basically, the coil looks like an “N”.
Coils for air conditioners and heat pumps can be purchased cased or uncased. In other words, the coil can come in a custom-made cabinet or just a stand-alone coil. Usually, the stand-alone coil is purchased to replace an existing coil that is already installed in its own cabinet. A cased coil is also installed in the ductwork near the air handler. This all depends on the installation, the air handler, and the configuration.
Materials and Maintenance | Evaporator Coil Air Conditioners
There are some special-order evaporator coils that are all copper. These are normally used in health care facilities. Copper inhibits the growth of mold and mildew, thus the reason why it is used in healthcare facilities. These coils are extremely expensive compared to the typical coils made from copper with aluminum fins.
The refrigerant changes state in the evaporator coil. In the evaporator coil, the change of state is from a liquid to vapor while in the condenser the change of state is from a vapor to a liquid. This is all necessary for the process of refrigeration to work properly. The typical evaporator coil is constructed of copper with aluminum fins surrounding the copper coils.
The aluminum fins add surface area to the copper coils and enhance the heat exchange rate making the coils more efficient. Although some manufacturers are switching to all-aluminum coils in both the condenser and the air handler evaporator coil. For more on this, you can read our article titles aluminum versus copper coils.
Coil Maintenance | Evaporator Coil Air Conditioners
The best way to maintain evaporator coils is to keep a good clean filter in your system. Additionally, it is also a good idea to make sure you have good tight ductwork. Small leaks in the return duct can cause your evaporator coil to load up with dust and dirt.
This inhibits airflow and eventually will cause the system to fail. It is essential that the coil gets the designed amount of airflow across the coil for the heat exchange process. Clogged air filters have a detrimental effect on the system also. Furthermore, having no air filter in the system is very bad and WILL lead to failure. Lastly, make sure you take care of your evaporator by keeping a good clean filter in the system.
Evaporator Coil for Heat Pumps & Air Conditioners