Water Cooled Air Conditioner

Water cooled air conditioner is also called water cooled condenser as its function is to reject the heat that was absorbed by the refrigerant in the evaporator. Water is used to cool the hot air refrigerant(180°F or 82°C) from the compressor by pumping counter-flow water in the condenser.

The water used can be a wastewater system in which the water is thrown away into the drain after being used. Wastewater system is not encouraged as it is wasteful and many states prohibit its use. A better option but higher cost is to recirculate the water by using a ccoling tower. The cooling tower will reject the heat from the water by forced draft or natural draft.

Water Cooled Air Conditioner Types

Water cooled air conditioner is superior to air cooled air conditioner as it can operate at lower condensing temperatures. Water has higher specific heat compared to air hence its efficiency is higher than air. It is usually used for capacity in excess of 20 tons.

You do not see a lot of this system in residential houses as it has a higher equipment cost, requires more maintenance  and higher installation cost. For this reason, the air-cooled air conditioner is more widely used in residential houses, cost-sensitive shops and small factories.

There are 3 main types of water cooled air conditioner condensers.

Tube-Within-A-Tube

In this design, the inner tube is inserted into the bigger outer tube and both pipes are formed into the shape of a coil to save space. This is the most commonly used design as it is easy to manufacture.

Water will flow through the inner tube and cools the refrigerant that is flowing in the outer tube. The refrigerant is also cooled by the air in the room. The inner tube can be designed to have grooved inner tube to increase the heat transfer between the refrigerant and the water.

Take note that the water and the refrigerant are designed to flow in opposite directions. This is known as counter-flow arrangement and its purpose is to keep the difference in temperature between them consistent throughout the length of the heat exchange.

As the condenser is shaped into a coil, cleaning the inner tube from mineral deposits of the water mechanically using brush is not possible. The only way to get rid of the deposits is to use suitable chemical to breakdown the minerals and flushed them out from the tube.

Shell and Coil

This configuration of condenser consists of a shell(can be steel) which contains a coil of tube which is usually made from copper inside it. The water will flow through the coil to cool the hot gas refrigerant in the shell. Hot air is usually feed from the top of the shell and condenses as it flows down and contact the coil.  The gas that condenses is further cool down into subcooling state at the bottom of the shell.

The minerals that is deposited on the coil from the water cannot be cleaned mechanically as it is located inside the shell. The only way to clean it is to use chemicals to flush out the minerals.

Shell and Tube

This type of condenser has a steel shell with many copper tubes inside it. As the cost to produce it is relatively high, it is only used in higher capacity air conditioning systems.

Shell and Tube heat exchanger. Photo by S.J. de Waard

Water is circulated in the tubes to cool the refrigerant that flows into the shell from the top. The shell also acts as a receiver. The subcooled liquid refrigerant is channeled out from the condenser for use in the next stage of the cooling process.

The tubes can be removed from the shell and cleaned out of mineral deposits in them.

Water Cooled Air Conditioner and Cooling Towers

Instead of channeling the hot water away to ponds or drainage system after it is used to take the heat from the refrigerant, the water can be cooled and then recirculated by using a cooling tower. Cooling tower is used to reject the heat from the water to the air. As the tower is exposed to water and air, it must be corrosive resistant hence the materials used to build it can be copper, plastic or stainless steel.

The hot water is piped away from the condenser and feed into the cooling tower which is located away from noise-sensitive premises. The cooled water that comes out from the cooling tower is then piped back to the condenser and the whole process repeats.

Cooling Tower

Here are the 2 common types of heat rejection method in the cooling tower.

●      Natural Draft uses the natural air to cool the water.

●      Forced Draft uses a fan to move the air over the wetted surface of the warm water.