The evaporator coil is the component in the system that absorbs heat from the conditioned space. It is similar in design to the air-cooled condensing coil. It is also finned to create more area to contact air flowing across it. The evaporator coil is designed for a specific purpose, to control humidity and temperature. Some coils are designed for high de-humidification, others are not. Earlier in the book, I mentioned that perfect conditions would be 72 degrees F., and a 50% R.H. for most human beings. A special design is required to accomplish this. If an evaporator is being used to keep vegetables and fruit from spoiling, a different type of coil is needed for the removal of heat and not the moisture contained in the product. This is only one example of many applications. Each evaporator is different and is designed to perform a specific task.
The refrigerant is pumped into the evaporator coil and pressure is dropped upon entering. The entrance is usually at the bottom of the coil. The refrigerant enters the coil as a liquid and begins absorbing heat. By the time the refrigerant reaches the top rows of the evaporator coil, it should have boiled and turned into a cool vapor. It is this cooled vapor that returns to the compressor to cool its windings and then it is recycled into a liquid to be circulated again.
Boiling temperatures of refrigerants at one (1) atm of pressure.
| R-12 | -21.62 degrees F. |
| R-22 | -41.4 degrees F. |
| R-500 | -28.0 degrees F. |
