Working Principle of Condenser and its Types

High side equipment: The pressure of the refrigerant in the condenser is very little that at the compressor discharge. The pressure at compressor discharge is higher than at any other part of the system. Hence the condenser and other equipment in the system between compressor discharge and expansion valve are referred to as high side equipment.

Low side valve equipment: Since the refrigerant in the evaporator is at low pressure compared to that in the condenser, the evaporator and auxiliaries between the expansion valve and the compressor intake are often referred to as low side equipment.

As the name implies, a condenser should be designed to condense effectively the compressed refrigerator vapor. It is the condenser that the refrigerant must give up the heat absorbed in the evaporator plus the heat added by the compressor. Good design further provides for some sub-cooling of liquid refrigerant before it leaves the condenser.

There are three different types of condensers
1. Air cooled condenser
2. Water cooled condenser
3. Evaporative condenser (combination of air and water cooled)

Air cooled condenser: The condenser consists of a finned continuous tube coil. The compressor discharged vapor enters the top of the coil and liquid leaving at the bottom from where it flows into the receiver located under the base. A fan mounted on the compressor-motor pulley blows air across the condenser coil. The unit should be located in a well-ventilated and preferably cool space. The lower the ambient air temperature, the less power required for given capacity. The main advantage of this type of condenser is the simplicity and low installation cost. They are mostly used in self-contained unit such as domestic refrigerators, freezer cabinets, display cases, water cooler and air room conditioners.
Water cooled condensers: Water cooled condensers are used with compressors of 1 hp and larger. They usually constitute the most economical choice of condenser where an adequate supply of clean inexpensive water of minimum corrosion is available with adequate and inexpensive means of water disposal. This type of condenser use water for cooling heated refrigerant and change to liquid. The condensers themselves may be of several types
1. Double pipe condensers
2. Double copper tube condensers
3. Shell and coil condensers
4. Shell and tube condensers

In water cooled condensers, the lower the water quantity used, higher is the condensing temperature and greater the power costs. Conversely, the higher the water quantity used, lower will be the condensing temperature and smaller the power costs. Therefore, there should be optimum sum of water flow that will produce minimum sum of water and power cost.
Evaporative condensers: This type of condenser is developed to alleviate the problem arising from the use of numerous water cooled condensers in small air conditioning system. The evaporative condensers are designed to combine the function of condensers and cooling tower.

Air is blown in through an opening near the bottom, flows upward across the refrigerant coil, through the sprays and eliminators and into the fan and discharged at top of the unit. The refrigerant condensing coil is usually of extended surface or finned type. The refrigerant enters at the top of the coil and flows across and downward. The condensed liquid drains into the receiver, frequently located in the water tank in order to sub-cool the liquid refrigerant further. Water from the tank is withdrawn by pump mounted on the unit and is discharged through spray nozzles directed downward over the refrigerant coil.

Since, 3 to 5 % of the water circulated evaporates, make-up water is admitted to the tank through float operated valve. Partial evaporation increases the salt concentration of water and therefore treatment of water and continuous overflow is recommended. Water treatment should also be used to reduce scale formation on warm coil. The unit should have provision of draining if sub-freezing temperature occurs. In cool water, it may not be necessary to use any water and the unit then operates as air –cooled condenser.