Evaporative condenser

A condenser is a heat exchanger where compressed & superheated refrigerant releases the heat to the environment. For instance, a refrigerant with condensing temperature of 25 °C enters a condenser that uses an ambient air (20 °C). The refrigerant is probably superheated due to the compression work, thus before condensing, the refrigerant is quickly de-superheated. Once the refrigerant reaches its condensing temperature (i.e. dew point), the refrigerant starts condensing and temperature is held at 25 °C. The driving force of the heat transfer between the ambient air and the refrigerant is the temperature difference. As always, heat flows from higher temperatures to lower temperatures.

 

Let's assume the condenser is designed to have 5 °C difference between the ambient and the refrigerant. If the weather gets colder, the condensation temperature of the refrigerant will also decrease, which will reduce the compressor load. The condenser operation affects the refrigeration system efficiency significantly. 

 

An evaportive condenser sprays water on the condensing coil and uses fan to draw ambient air. Thin layer of water on the condensing coil evaporates and takes heat away. Different to a fan condesner, the operating condition of an evaporative condenser depends on wet-bulb temperature of ambient air. 

 

Control of evaporative condenser is usually done by changing the fan speed.