There are four main parts of refrigerating and air-conditioning systems, these are: compressor, condenser, throttling or expansion valve and the evaporator. The refrigerant leaving the compressor is in the gaseous state and at a high pressure and temperature. This refrigerant then enters the condenser where it loses the heat to the coolant, which can be air or water.
After passing through the condenser the refrigerant gets condensed but still remains at high pressure. It comes out in a partially liquid and gaseous state and then enters the throttling or expansion valve.
There are three types of condensers: air cooled, water cooled and evaporative. These have been described below.
1) Air cooled condensers: Air cooled condensers are used in small units like household refrigerators, deep freezers, water coolers, window air-conditioners, split air-conditioners, small packaged air-conditioners etc. These are used in plants where the cooling load is small and the total quantity of the refrigerant in the refrigeration cycle is small. Air cooled condensers are also called coil condensers as they are usually made of copper or aluminum coil. Air cooled condensers occupy a comparatively larger space than water cooled condensers.
Air cooled condensers are of two types: natural convection and forced convection. In the natural convection type, the air flows over it in natural a way depending upon the temperature of the condenser coil. In the forced air type, a fan operated by a motor blows air over the condenser coil.
2) Water cooled condensers: Water cooled condensers are used for large refrigerating plants, big packaged air-conditioners, central air-conditioning plants, etc. These are used in plants where cooling loads are excessively high and a large quantity of refrigerant flows through the condenser.
There are three types of water cooled condensers: tube-in-tube or double pipe type, shell and coil type and shell and tube type. In all these condensers the refrigerant flows through one side of the piping while the water flows through the other piping, cooling the refrigerant and condensing it.
3) Evaporative condensers: Evaporative condensers are usually used in ice plants. They are a combination of water cooled and air cooled condensers. In these condensers the hot refrigerant flows through the coils. Water is sprayed over these coils. At the same time the fan draws air from the bottom side of the condenser and discharges it from the top side of the condenser. The spray water that comes in contact with the condenser coil gets evaporated in the air and it absorbs the heat from the condenser, cools the refrigerant and condenses it.
Evaporative condensers have the benefits of water cooled as well as air cooled condenser, hence it occupies less space. However, keeping the evaporative condenser clean and free of scale is very difficult and requires lots of maintenance. Hence they are not favored by HVAC designers.