Chillers are machines used to dehumidify or cool fluids. There are various types of chillers classified on the basis of working fluid used, working mechanism used etc.
This article explains how does a chiller work, different types of chillers used in industry and general information about compressors used in air cooled chillers.
How does an air-cooled chiller work?
Ever seen multiple fans installed on the top of a building? They are used for cooling purposes inside the building. These fans are a part of a bigger system known as air cooled chiller.
Chiller is a machine that absorbs heat using vapour compression cycle, vapour absorption cycle or vapour adsorption cycle. The cool fluid can be passed through a heat exchanger for further applications. Concepts of thermodynamics are used in air cooled chillers to cool the fluid or dehumidify air.
Chillers collects heat from water and sends it back to air handling unit which uses cool water for its operation. After AHU’s operation, the water temperature rises and is brought back to the air chiller.
How does an industrial chiller work?
The main purpose of industrial air chiller is to cool the water and send it back to the AHU (Air Handling Unit). After AHU does its specified task, the water inside the AHU becomes warm. This warm water is sent back to the inlet of chiller. This cycle continues till the end of AHU’s operation.
The air chiller absorbs heat from the processed water that comes into the inlet of the chiller. Heat is absorbed with the help of chiller’s evaporator.
After the liquid refrigerant passes through evaporator, its phase changes to gas and pressure decreases in this process. After compression, the refrigerant that leaves has high pressure and high temperature.
This gas enters the condenser where it is cooled by condensing fans. The cooling fans blow away the heat into ambient hence it is suggested to install air chillers outside the room or at a place where dumping heat is not an issue.
An industrial air chiller has following components- Evaporator, condenser, compressor, pump and cooling fans.
- Evaporator-It takes away heat from the water to change the phase from liquid to gas.
- Compressor-Temperature and pressure of the gas is increased by compressing the gas in compressor.
- Condensing fans/cooling fans-The cooling fans blow away the heat from the refrigerant reducing the temperature of gas.
- Condenser-The phase changes back to liquid inside the condenser.
What are industrial chillers used for?
Industrial chillers are used for cooling mechanisms, products and a wide range of machinery. It can be centralized where one chiller can be used for multiple applications or decentralized where each and every application has one dedicated chiller.
Chillers are used in plastic industries, metal cutting work oils, injection and blow moulding, cement processing. They are also used in gas turbine cooling system, high heat applications such as MRI and lasers in hospitals.
Liquid cooled chillers are used for indoor operations due to as liquid absorbs the rejected heat. Air cooled chillers are meant for outdoor installations because the heat is rejected in the ambient. Hence, most air cooled chillers are installed at the top of buildings.
Types of compressors used in air cooled chillers
There are various types of compressors that can be used in chillers depending on the load requirements in the application. Following are the compressors that can be used in chillers-
- Reciprocating compressor-A simple positive displacement pump which used a piston to deliver gas at high pressure. The gas enters the cylinder in the suction stroke when the piston is at bottom dead centre. The gas is compressed in the next stroke when the piston move towards the top dead centre. Compressed gas leaves through the delivery valve. This type of compressors deliver compressed gas in pulsations.
- Rotary screw compressor-Rotary compressors are used in large sized refrigeration applications such as chillers. These have rotary type positive displacement mechanism and provide continuous delivery of compressed gas unlike reciprocating compressors which have pulsations. Rotary compressors are more quiet in operation.
- Vane compressor-Most common type of compressor is the vane compressor. It uses centrifugal force to compress the gas. These compressors uses vanes instead of helical screws to generate compressed air.
- Scroll compressor-A scroll compressor uses two spiraled scrolls for compressing the gas or refrigerant. Usually one scroll is fixed and other orbits with a little offset without rotating. The tapped gas between the scrolls get compressed due to the relative motion between scrolls. Its efficiency is slightly higher than reciprocating compressors.
Image credit: No machine-Kompresors, CC BY-SA 3.0
Water cooled chillers
As the name suggests, water cooled chillers use water instead of air for cooling. It uses latent heat for cooling purposes.
External cooling towers supply water that is used to cool the gaseous refrigerant in the condenser. Inside the condenser, refrigerant’s phase changes. The gaseous refrigerant turns into liquid refrigerant and is then re-circulated in the system.
Advantages and disadvantages of water cooled chillers
Every mechanical component has its own pros and cons. Designers have to make a trade off between pros and cons to make the best design suitable for the particular application. Following are the advantages and disadvantages of water cooled chillers
Advantages of water cooled chillers-
- They are more efficient than air chilled coolers.
- They don’t create much noise while operating.
- They can be used in both small scale and commercial scale applications.
Disadvantages of water cooled chillers-
- Due to continuous requirement of water, water cooled chillers are not feasible to use in areas having water shortage problems.
- As the number of components are increased (cooling tower and pumps), installation cost of water cooled chillers is more.
Vapour compressed chillers vs vapour absorbed chillers
Vapour compressed and vapour absorbed chillers are both air cooled chillers. The principle difference between vapour compressed chiller and vapour absorbed air chiller is the way of cooling.
| Vapour compressed chillers | Vapour absorbed chillers |
| Vapour compressor chillers use following components- evaporator, condenser, compressor and an expansion unit. Refrigerant extracts unwanted heat, this refrigerant is pumped by the action of compressor. | Vapour absorption chillers use same components as vapour compressed chillers except compressor. Instead of compressor, there is an absorber, generator and a pump. Heat source itself is used to pump refrigerant around the system for cooling purposes. |
It is clear that vapour absorbed chiller has more parts but it is cheaper to operate as it does not need any compressed air for operation.
Hi ….I am Abhishek Khambhata, have pursued B. Tech in Mechanical Engineering. Throughout four years of my engineering, I have designed and flown unmanned aerial vehicles. My forte is fluid mechanics and thermal engineering. My fourth-year project was based on the performance enhancement of unmanned aerial vehicles using solar technology. I would like to connect with like-minded people.