What Is a Chiller Unit?
A chiller unit is a device that cools a heat medium such as water.
It is also called a chilling unit. There are air-cooled, water-cooled, and refrigeration types, and they are selected according to the required heat medium temperature, application, and operating environment. They are widely used in a wide range of applications, such as removing excess heat generated by industrial machinery and other equipment, maintaining a constant temperature, and central air conditioning. Despite the name “chiller,” there are also hot water chillers with built-in heaters, which can be used in facilities that require hot water circulation.
Uses of Chiller Units
Chiller units are used in the following diverse applications and are indispensable to modern industry and social infrastructure:
- Excess heat treatment in general industrial facilities.
- Temperature control of resin molding dies.
- Prevention of overheating during cutting in metal processing equipment.
- Suppression of heating due to reaction heat in plating equipment.
- Preventing heating of bearings in rotating parts.
- Central air conditioning of buildings and various facilities.
- Temperature control of supply water for hydroponics.
- Water temperature control in aquaculture farms.
- Air conditioning and water temperature control in heated swimming pools and plastic greenhouses.
Principle of Chiller Units
Chiller units use a heat medium to cool objects, or to heat them, depending on the application. A similar function is performed by a heat exchanger.
The main difference between chiller units and heat exchangers is design. Chiller units have a cooling system for the heat transfer fluid in the circulation path, whereas a heat exchanger has no cooling system for the heat transfer fluid, and heat is exchanged directly between the fluid and the heat transfer fluid. There are two types of chiller unit cooling systems: vapor compression and heat absorption.
In terms of cost, heat exchangers, which do not require cooling facilities, generally tend to be cheaper. Even if there are cost limitations, when selecting equipment, great care must be taken to ensure that the heat exchange capacity, stability of the heat exchange process, running costs, maintenance costs, and other factors will not cause problems after the start of operation.
There are three general types of chiller units as described above. In addition to these types, there is a wide range of products that vary in terms of the amount of heat medium circulated, heat exchange capacity, etc. The principles and features of each type are described below. The principles and features of each type are as follows:
1. Air-Cooled Chiller Units
Equipped with a heat exchanger to cool the heat medium, the built-in fan air-cools the heat exchanger to remove sensible heat from the heat medium and cool it. The sensible heat is then released into the atmosphere. Water is often used as the heat transfer medium, and chilled water of 3 to 35°C is generally circulated.
2. Water-Cooled Chiller Units
The chiller units are equipped with a heat exchanger to cool the heat medium in the same way as air-cooled units, but water is used to cool the heat exchanger. Unlike air-cooled units, water-cooled chiller units do not have a built-in fan, making them low-noise, clean, and free of heat emissions, so they can be used indoors. The internal structure is more complex, as piping and valve elements for cooling water circulation are required.
3. Refrigeration Chiller Units
This type incorporates a chiller equipped with a refrigeration cycle mechanism to cool the heat medium, which is then cooled by a heat exchanger. Since the chiller is equipped with a refrigeration unit, the temperature of the heat transfer fluid can be cooled down to -70°C (-94°F) or lower. Ethylene glycol or fluorine fluorine is used as the heat transfer fluid to prevent freezing. This is used when the heat load is high or when the object to be cooled needs to be below freezing. This is the most complex structure, as it is equipped with a refrigerator and requires piping for refrigerant circulation.
Other Information on Chiller Units
Chiller Units Heat-Transfer Cooling System
Chiller units can be classified into the following heat-transfer cooling methods:
- Vapor Compression Type
Vapor compression chillers consist of a compressor unit that converts heated vaporized refrigerant into cooled liquid for cooling. Vapor compression systems are usually installed together with air-cooled, water-cooled, or evaporative condensers. - Heat Absorption Systems
Absorption chillers use less expensive, low-energy cooling units that induce refrigerant in a heating process in a single-phase cooling cycle. These units consist primarily of a water-based refrigerant with lithium bromide as the absorbent.