Industrial Chillers

The types of chillers are water cooled and air cooled, divided into vapor absorption chillers and vapor compression chillers, each of which uses a different technique for removing the collected heat from the chiller system. In the case of an air cooled chiller, fans remove heat from the chiller by circulating air. With water cooled chillers, heat from the process is removed by water. Absorption chillers use a concentrated absorbent agent such as lithium bromide or ammonia water to absorb the coolant while the heat is removed by cooling water.

Types of Industrial Chillers

Although the majority of chillers are air or water cooled, some of the distinguishing features that separate the different types of chillers is the type of compressor they use. Vapor compression chillers use an electrically driven mechanical compressor to force refrigerant through the system. The more popular types of chillers are vapor absorption chillers, divided between air cooled and water cooled.

Vapor Compression Chillers

Most of the components of a vapor compression chiller are the same as vapor absorption chillers, which are an evaporator, condenser, and expansion valve. However, what differentiates vapor compression chillers from vapor absorption ones is the absence of a compressor. Instead, vapor compression chillers have an electrically driven mechanical compressor that forces the refrigerant through the system.

The principle behind the operation of a vapor compression chiller is the same as all chillers, which is to remove heat and replace it with cool air. They use a refrigerant that absorbs heat from a space and brings it back to the evaporator that removes the heat, using fans for an air cooled chiller or water for a water cooled one. Aside from the driving mechanism of a vapor compression chiller, the other basic functions are the same.

Vapor Absorption Chiller

Vapor absorption chillers work on the principle of separating and recombining fluids, such as refrigerant and absorbent, to create cooling. The process of an absorption chiller includes ammonia water cycling or lithium bromide cycling. With ammonia water vapor absorption chillers, water serves as the absorbent while an ammonia-water solution acts as the refrigerant. In a lithium bromide system, lithium bromide is the absorbent, while water is the refrigerant.

Air Cooled Systems vs. Water Cooled Systems

Once the chiller system collects the heat, it has to be removed and released into the atmosphere. For all industrial chiller systems, two methods are used to achieve this: air cooling and water cooling. These two methods are a major factor in determining certain aspects of the overall chiller system.

• Air Cooled

  Air cooled systems use the surrounding air of the chiller to eject the air out of the system and into the atmosphere. They consist of propeller-driven fans to pull air over the condenser's coils. As the air moves over the coils, heat is transferred to the air and released into the atmosphere. Major factors in the use of air cooled chillers are their size and ease of installation. Since they use the ambient air for the heat transfer process, they can be installed outside of a building or on its roof.

• Water Cooled

  Water cooled chillers have water cooled condensers connected to a cooling tower. The essential element for water cooled chillers is circulating water that comes from the cooling tower and cools the gaseous form of the refrigerant. Once the refrigerant gas is cooled, it undergoes a phase change back to a liquid and is recirculated through the system.

Unlike air cooled chillers, water cooled chillers are normally located inside a building, which protects them from the effects of the elements. They are more efficient and produce less noise than air cooled chillers. However, water cooled systems are expensive and take up more room due to the use of cooling towers.

Types of Compressors

The compressor of a chiller removes the heat from the refrigerant by taking low-pressure and low-temperature refrigerant in a gaseous form and compressing it into a high-pressure and high-temperature form. Once the refrigerant has been compressed, it moves on to the condenser coils, where heat is removed using water or air.

Centrifugal Compressor

A centrifugal compressor has impellers that rapidly rotate the refrigerant and force it to the compressor's walls. As the rate of the revolutions increases, the pressure and temperature in the refrigerant rise; then, it is released to the condenser. Centrifugal compressors are used with high capacity, large systems of up to 6000 tons.

Reciprocating Compressor

A reciprocating compressor has a piston, cylinder, and crankshaft. The gas enters the cylinder through the intake by the reverse movement of the piston that sucks it in. Once the chamber of the cylinder is full, the reciprocating motion of the piston compresses the gas and discharges it into the condenser.

Scroll Compressor

Scroll compressors have two spiral plates with one stationary and one rotating. As the rotating plate spins, it compresses the refrigerant. During the motion of the moving plate, small pockets of refrigerant are pushed between the scrolls, reducing the volume of the refrigerant.

Screw Compressors

Screw compressors have two intermeshed helical rotors with male lobes and female gullies that compress the refrigerant and increase its pressure. They are the quietest type of compressor and have fewer moving parts. The suction, compression, and discharge happen in a single linear motion.