Industrial Chillers: Working Principle and Key Components

I. What Is a Chiller?
A chiller is what we commonly refer to as an industrial water chiller. An industrial chiller is a refrigeration system used to lower the temperature of spaces and process fluids by removing heat from the system and transferring it elsewhere. Industrial chillers are indispensable for the pharmaceutical industry, where temperature and humidity require strict control.

II. Why Use a Chiller?
Chillers include air-cooled chillers and water-cooled chillers. The pharmaceutical industry uses chillers because of strict cleanroom temperature and humidity management requirements.

III. Working Principles
The working principle of an industrial chiller is based on the following operating principles.

Phase Change: When heated, a liquid refrigerant undergoes a phase change into a gas; when the gaseous refrigerant is cooled, it condenses back into a liquid.

Heat Flow: Thermal energy always flows from a region of high concentration to a region of low concentration.

Boiling Point: Reducing the pressure above a liquid lowers its boiling point, while increasing the pressure raises its boiling point.

IV. How Does a Chiller Work?
Industrial chiller systems are driven by two working principles: heat absorption and vapor compression.

Heat-absorption chillers incorporate heat exchangers that draw heat from any related process and dissipate it outward. Heat exchangers typically include pipes containing a cooling fluid (air, water, or a mixture of water and other liquids).

Vapor-compression chillers achieve cooling by circulating refrigerant through pipes in the process requiring cooling. This transfers heat from any associated process into the refrigerant, which then circulates to the refrigerant system, cools the chiller fluid, and prepares for a new process cooling cycle.

A chiller consists of four key components: the evaporator, compressor, condenser, and expansion device. In addition, every chiller system contains a refrigerant.

The process begins with low-pressure refrigerant entering the evaporator. Inside the evaporator, the refrigerant is heated, causing it to undergo a phase change into a gas. Next, the gaseous refrigerant enters the compressor, where the pressure increases. The high-pressure refrigerant enters the condenser, which uses cooling water from a cooling tower or ambient air to reject heat, condensing it into a high-pressure liquid. The condensed refrigerant then enters the expansion device, which has a valve that acts as a metering device to restrict refrigerant flow. This reduces the refrigerant pressure and begins the cooling process again. The entire process is called the refrigeration cycle.

V. Basic Components of a Chiller
Central chiller components include the following parts:

Condenser
The function of the chiller condenser is to remove heat from the refrigerant circulating through the chiller. This is achieved by circulating water between a cooling tower and the condenser in water-cooled variants, or by blowing air across the condenser coils in air-cooled chillers.

Compressor
The compressor is the driving unit of any chiller system. It generates the necessary pressure gradient to propel the refrigerant through the chiller to achieve process cooling. Various compressors are available, with the most commonly used types including centrifugal, screw, and reciprocating compressors.

Evaporator
The evaporator is located between the expansion valve and the compressor, and transfers heat from any associated process into the circulating refrigerant. Depending on the chiller configuration, this heat is then rejected to a cooling tower or to the air.

Thermal Expansion Valve
The thermal expansion valve, located between the compressor and the evaporator, expands the refrigerant passing through it. This action reduces the pressure and increases the heat absorption capacity of the evaporator.

Power Unit
All air-cooled and water-cooled chillers have a power unit that controls the electrical power flowing through the system. Power unit components typically include a starter, a power monitoring panel, and circuit breakers.

Water Tank
These devices can be mounted on the evaporator of the chiller system or on its water-cooled condenser. Their purpose is to effectively guide the water flow.