A Complete Guide to Different Chiller Systems

What Is a Chiller?

A chiller is a refrigeration machine that removes heat from water or another fluid and produces a cooled liquid, commonly called chilled water.

The chilled water is circulated through pipes to air handling units (AHUs), fan coil units (FCUs), or industrial equipment. These systems use the chilled water to remove heat from indoor air or manufacturing processes.

Unlike a conventional air conditioner that cools air directly, a central chiller system generally cools water first and distributes that cooling throughout a building or facility.

Common applications include:

• Commercial building air conditioning

• Hospital and laboratory cooling

• Industrial process temperature control

• Food and beverage production

• Pharmaceutical manufacturing

• Data centre cooling

• Plastic and chemical processing

• District cooling systems

Chillers are available in different capacities and configurations. Their selection depends on the required cooling load, operating environment, energy supply, and application.

How Does a Chiller Work?

Most electric chillers operate using a vapour-compression refrigeration cycle. This process transfers heat from the chilled-water circuit to the outside environment.

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The basic refrigeration cycle involves four main stages.

1. Evaporation

The evaporator is the section where heat is removed from the water or process fluid.

Warm return water passes through the evaporator, where it transfers heat to the refrigerant. The refrigerant absorbs this heat and changes from a liquid into a vapour.

As heat leaves the water, its temperature decreases.

2. Compression

The refrigerant vapour moves to the compressor.

The compressor increases the refrigerant's pressure and temperature, preparing it for heat rejection in the condenser.

The compressor is one of the most important components because its design has a major influence on chiller capacity, efficiency, and operating characteristics.

3. Condensation

The hot, high-pressure refrigerant enters the condenser.

Here, it releases the heat absorbed in the evaporator. Depending on the chiller design, this heat is transferred to outdoor air or condenser water.

As the refrigerant loses heat, it changes back into a liquid.

4. Expansion

The liquid refrigerant passes through an expansion device, such as an electronic expansion valve.

Its pressure and temperature decrease before it returns to the evaporator.

The cycle then repeats.

The cooled water circulates through the building or industrial process, absorbs heat, and returns to the chiller for cooling again.

Main Ways to Classify Chillers

Chillers are commonly classified using two separate characteristics:

1. Heat rejection method: How the system releases the collected heat, such as air-cooled or water-cooled.

2. Compressor or refrigeration technology: How the refrigerant is compressed or how the refrigeration cycle is driven.

These classifications are different. For example, a screw chiller can be air-cooled or water-cooled.

Types of Chillers Based on Heat Rejection

1. Air-Cooled Chiller

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An air-cooled chiller releases heat directly into the surrounding air through a condenser coil and fans.

The refrigerant transfers heat to the condenser coil, and fans move outdoor air across the coil to carry the heat away.

Main features:

• Uses fans to remove heat.

• Does not require a cooling tower.

• Generally has a simpler installation arrangement.

• Requires less condenser-water infrastructure.

• Performance can be affected by high outdoor temperatures.

Advantages:

• Relatively straightforward installation.

• No cooling tower or condenser-water circuit is required.

• Suitable for locations where water availability is limited.

• Can be practical for smaller and medium-sized cooling requirements.

Limitations:

• Fan operation can produce noise.

• High outdoor temperatures may reduce cooling performance.

• Air-cooled systems may use more electricity than comparable water-cooled systems under certain operating conditions.

• Outdoor condenser coils require regular cleaning and maintenance.

Common applications:

• Office buildings

• Retail stores

• Hotels

• Small manufacturing facilities

• Clinics and laboratories

• Commercial buildings with limited plant space

2. Water-Cooled Chiller

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A water-cooled chiller transfers heat from the refrigerant to condenser water. This water is circulated through a cooling tower, where heat is released into the atmosphere.

The cooling tower uses contact between water and moving air to remove heat through evaporation and sensible heat transfer.

Main features:

• Uses a water-cooled condenser.

• Usually operates with a cooling tower.

• Requires condenser-water pumps and piping.

• Often suitable for larger cooling loads.

• Requires water treatment and regular maintenance.

Advantages:

• Can offer high energy efficiency in large installations.

• Suitable for continuous operation.

• Often effective for large commercial and industrial cooling systems.

• Can provide good performance when properly designed and maintained.

Limitations:

• Requires a cooling tower and additional equipment.

• Uses water through evaporation and other system losses.

• Requires water treatment to manage scale, corrosion, and biological growth.

• Installation and maintenance arrangements are more complex.

Common applications:

• Large hospitals

• Shopping malls

• Airports

• Industrial facilities

• Data centres

• Hotels and large commercial buildings

Air-Cooled vs. Water-Cooled Chillers

Neither option is suitable for every location. Water availability, local climate, electricity costs, cooling demand, and maintenance resources should all be considered.

Types of Chillers Based on Compressor Technology

The compressor is responsible for increasing refrigerant pressure and moving it through the refrigeration cycle. Different compressor designs provide different operating characteristics and capacity ranges.

1. Scroll Chiller

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A scroll chiller uses a scroll compressor containing two spiral-shaped elements. One scroll remains stationary while the other moves in an orbiting motion.

The movement traps refrigerant vapour and gradually compresses it toward the centre of the scroll assembly.

Main characteristics:

• Relatively simple mechanical design.

• Fewer moving parts than many traditional reciprocating designs.

• Generally quiet operation.

• Often available in compact packaged systems.

• Multiple compressors can be combined to increase capacity.

Advantages:

• Suitable for smaller cooling loads.

• Can offer reliable operation.

• Compact equipment arrangement.

• Multiple compressor stages can help match changing cooling demand.

Limitations:

• Individual compressor capacity is relatively limited.

• Large facilities may require several compressor modules.

• Performance depends on the model and capacity-control arrangement.

Applications:

• Small commercial buildings

• Clinics

• Laboratories

• Retail facilities

• Small industrial processes

• Equipment cooling

2. Screw Chiller

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A screw chiller uses one or more rotating screw-shaped rotors to compress refrigerant.

As the rotors turn, refrigerant vapour becomes trapped between the rotor surfaces and compressor housing. The trapped volume decreases, increasing the refrigerant pressure.

Screw chillers are available in air-cooled and water-cooled configurations.

Main characteristics:

• Designed for medium and larger cooling requirements.

• Uses rotary compression technology.

• Available with different capacity-control methods.

• Can operate under varying load conditions.

• Often used in industrial and commercial facilities.

Advantages:

• Suitable for continuous operation.

• Can provide good part-load performance when properly selected.

• Available in a wide range of capacities.

• Suitable for many industrial cooling applications.

Limitations:

• Requires appropriate lubrication and maintenance in oil-lubricated designs.

• Compressor and control systems can be more complex than smaller packaged units.

• Operating noise and vibration should be considered.

Applications:

• Manufacturing plants

• Food processing facilities

• Hospitals

• Commercial buildings

• Pharmaceutical facilities

• Industrial process cooling

3. Centrifugal Chiller

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A centrifugal chiller uses a high-speed rotating impeller to increase the velocity of refrigerant vapour. A diffuser then converts much of that velocity into pressure.

Unlike positive-displacement compressors, which trap and compress a fixed volume of gas, centrifugal compressors use dynamic forces to increase refrigerant pressure.

Main characteristics:

• Commonly used in large cooling plants.

• Designed for high-capacity applications.

• Often available with advanced variable-speed controls.

• Usually water-cooled.

• Can provide high efficiency at suitable operating conditions.

Advantages:

• High cooling capacity.

• Strong efficiency potential in large installations.

• Suitable for central chilled-water plants.

• Advanced models can provide effective part-load performance.

Limitations:

• Requires careful engineering and system design.

• Performance can be affected by operating conditions and low-load operation.

• Generally requires specialized maintenance.

• Initial equipment and installation costs can be significant.

Applications:

• Large hospitals

• Airports

• Universities

• Shopping centres

• Data centres

• District cooling plants

• Large industrial facilities

4. Reciprocating Chiller

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A reciprocating chiller uses pistons moving inside cylinders to compress refrigerant vapour.

As the piston moves, it draws refrigerant into the cylinder, compresses it, and pushes it into the discharge line.

Reciprocating technology has been used in refrigeration and cooling systems for many years. Although many newer installations use scroll or screw compressors, reciprocating chillers remain relevant in certain applications and existing facilities.

Main characteristics:

• Uses piston-based compression.

• Can be designed with multiple cylinders.

• Available in different capacity configurations.

• Has a well-established mechanical design.

Advantages:

• Familiar technology.

• Suitable for selected smaller cooling applications.

• Can be serviced by technicians familiar with reciprocating equipment.

Limitations:

• More moving parts than many scroll designs.

• Vibration and noise may require attention.

• Maintenance needs can be higher in some configurations.

• Often less attractive than newer alternatives for large modern installations.

Applications:

• Older commercial cooling systems

• Small industrial refrigeration systems

• Specialized process cooling

• Certain low-temperature applications

5. Absorption Chiller

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An absorption chiller uses heat energy to drive the refrigeration process instead of relying on a conventional mechanical refrigerant compressor.

A common design uses water as the refrigerant and lithium bromide as the absorbent. Other absorption systems use different refrigerant and absorbent combinations, such as ammonia and water.

In a lithium bromide-water system, heat supplied to the generator separates refrigerant vapour from the absorbent solution. The refrigerant then passes through condensation, expansion, and evaporation stages. The absorbent captures refrigerant vapour from the evaporator and returns through the system.

Common heat sources include:

• Steam

• Hot water

• Natural gas or other direct-fired energy sources

• Industrial waste heat

• Heat recovered from combined heat and power systems

Advantages:

• Can use waste heat that would otherwise be unused.

• Requires relatively little electricity for the main refrigeration cycle.

• Can support facilities with suitable thermal energy sources.

• May reduce dependence on electrically driven compressors.

Limitations:

• Generally has lower thermal efficiency than electric vapour-compression chillers.

• Requires a suitable heat source.

• Often needs a larger heat-rejection system.

• Water treatment and operating conditions require careful management.

• Lithium bromide systems need protection against crystallization.

Applications:

• Hospitals

• Industrial facilities

• Combined heat and power plants

• Large commercial buildings with available waste heat

• Facilities with steam or hot-water networks

Absorption chillers are most attractive when suitable heat is available at a reasonable cost. They are not automatically more energy-efficient or less expensive to operate than electric chillers.

Comparison of Major Chiller Types

Capacity ranges overlap between manufacturers and models. The actual suitable range depends on the system design, refrigerant, cooling conditions, and application.

Important Components of a Chiller System

A complete chiller installation contains more than the chiller unit itself. Several components work together to transfer heat and distribute cooling.

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1. Evaporator

The evaporator transfers heat from the circulating water or process fluid to the refrigerant.

It is one of the main heat exchangers in the refrigeration cycle.

2. Compressor

The compressor increases refrigerant pressure and moves it through the system. Its design determines whether the machine is classified as scroll, screw, reciprocating, or centrifugal.

Absorption chillers use a different thermally driven process.

3. Condenser

The condenser releases heat from the refrigerant.

It may transfer heat to outdoor air or to a separate water circuit, depending on the chiller type.

4. Expansion Valve

The expansion valve controls the refrigerant flow into the evaporator and reduces its pressure.

Electronic expansion valves are used in many modern systems to improve control under changing operating conditions.

5. Chilled Water Pump

The chilled-water pump circulates cooled water from the chiller to air handling units, fan coil units, or industrial equipment.

6. Cooling Tower

A cooling tower is commonly used with water-cooled chillers. It removes heat from condenser water and releases it into the atmosphere.

7. Control Panel

The control panel monitors operating conditions and manages the chiller's operation.

It may monitor water temperatures, refrigerant pressures, compressor operation, flow rates, alarms, and energy consumption.

8. Piping and Valves

Pipes carry chilled water and condenser water through the system. Valves help regulate flow, isolate equipment, and support maintenance.

Common Applications of Chiller Systems

Chillers are used wherever controlled cooling is required for people, equipment, products, or manufacturing processes.

1. Commercial Buildings

Office towers, shopping malls, hotels, and large commercial complexes often use central chiller systems to provide air conditioning.

Chilled water is circulated to AHUs and FCUs that cool the indoor air.

2. Hospitals and Healthcare Facilities

Hospitals use chillers to support temperature control in patient areas, operating departments, laboratories, and other spaces.

Certain medical equipment and specialized areas may also require dedicated cooling systems.

3. Pharmaceutical Manufacturing

Pharmaceutical facilities use controlled cooling for production equipment, storage environments, and selected manufacturing processes.

Stable temperature control is important for maintaining process conditions and product quality.

4. Food and Beverage Processing

Chillers support cooling in food production, beverage manufacturing, dairy processing, and packaging operations.

They may be used to cool process water, equipment, and production areas.

5. Plastic and Chemical Industries

Industrial chillers are used to remove heat from manufacturing processes.

Examples include:

• Plastic injection moulding

• Extrusion equipment

• Chemical processing

• Industrial coating systems

• Metalworking operations

6. Data Centres

Data centres generate substantial heat through servers, networking equipment, and power systems.

Chillers may support cooling systems that maintain suitable operating temperatures for IT equipment. The exact design may involve chilled-water systems, air handling equipment, or liquid-cooling arrangements.

7. Manufacturing and Industrial Facilities

Many manufacturing processes require stable temperature control to maintain product quality, equipment performance, and operating consistency.

Industrial chillers can be designed to provide cooling for individual machines or larger process networks.

How to Choose the Right Chiller System

Selecting a chiller requires an understanding of the facility's cooling requirements and operating conditions.

1. Calculate the Cooling Load

The first step is determining how much heat the system must remove.

Cooling load calculations should consider:

• Building size and occupancy

• Equipment heat generation

• Outdoor design temperatures

• Operating hours

• Process requirements

• Future expansion

An oversized or undersized chiller can create performance and operating-cost problems.

2. Consider the Cooling Capacity

Chiller capacity is commonly measured in kilowatts (kW), refrigeration tons (TR), or British thermal units per hour (BTU/h).

One ton of refrigeration is approximately 3.517 kW of cooling capacity.

The selected capacity should match the calculated load, with suitable allowance for operating conditions and system design.

3. Compare Energy Efficiency

Chiller efficiency is a major factor in long-term operating expenses.

Common performance measurements include:

• COP (Coefficient of Performance): Cooling output divided by energy input. A higher value generally indicates better efficiency.

• EER (Energy Efficiency Ratio): A measure comparing cooling output with power consumption under specified conditions.

• kW/TR: Electrical input required per ton of refrigeration. A lower value generally indicates better efficiency.

• IPLV or NPLV: Measures performance across a range of operating loads under defined rating conditions.

Do not compare efficiency figures without checking whether the test conditions, system boundaries, and rating standards are the same.

Part-load performance is particularly important because many chiller systems operate below their maximum capacity for much of the year.

4. Evaluate the Installation Environment

The location and available infrastructure influence chiller selection.

Consider:

• Indoor or outdoor installation

• Available floor or roof space

• Ambient temperature

• Water availability

• Electrical supply

• Noise restrictions

• Ventilation requirements

• Access for maintenance

5. Review Maintenance Requirements

Different chiller types require different maintenance procedures.

Common activities include:

• Cleaning heat exchangers and condenser coils

• Checking refrigerant levels and system performance

• Inspecting pumps and motors

• Checking electrical connections

• Monitoring water quality

• Maintaining cooling towers

• Testing safety controls

A suitable maintenance plan can help reduce breakdowns and improve equipment life.

6. Check Refrigerant and Environmental Requirements

Refrigerants differ in their global warming potential, safety classification, operating pressure, and regulatory status.

Before purchasing a chiller, check the refrigerant used, its availability, applicable environmental rules, and the manufacturer's service support.

7. Calculate Total Ownership Cost

The initial purchase price does not represent the full cost of a chiller system.

A complete assessment should include:

• Equipment purchase

• Installation

• Electrical infrastructure

• Pumps and piping

• Cooling tower, where required

• Energy consumption

• Water treatment

• Maintenance

• Spare parts

• Refrigerant servicing

A system with a higher initial price may offer better long-term value if it operates more efficiently and has suitable maintenance support.

Common Chiller Operating and Maintenance Problems

Regular monitoring helps identify performance problems before they lead to equipment failure.

Chiller maintenance and refrigerant work should be carried out by qualified technicians following the manufacturer's instructions and applicable safety requirements.

Frequently Asked Questions

What are the main types of chillers?

The main types include air-cooled chillers, water-cooled chillers, scroll chillers, screw chillers, centrifugal chillers, reciprocating chillers, and absorption chillers. These categories describe different aspects of chiller design and can overlap.

Which chiller is most energy-efficient?

Large water-cooled centrifugal chillers can offer excellent efficiency when properly selected and operated. However, the best option depends on cooling load, climate, operating hours, part-load performance, and system design.

What is the difference between an air-cooled and water-cooled chiller?

An air-cooled chiller releases heat directly into outdoor air through condenser coils and fans. A water-cooled chiller transfers heat to condenser water, which usually passes through a cooling tower.

What is a screw chiller used for?

Screw chillers are commonly used in medium and large commercial buildings and industrial facilities. They can support continuous cooling and are available in air-cooled and water-cooled designs.

What is an absorption chiller?

An absorption chiller uses heat energy to drive the refrigeration cycle instead of relying mainly on an electric compressor. It may use steam, hot water, gas, or industrial waste heat as its energy source.

How long does a chiller last?

Service life depends on the design, operating conditions, maintenance quality, water treatment, and availability of replacement parts. Regular inspections and preventive maintenance help support reliable operation.

What is the difference between a chiller and an air conditioner?

An air conditioner generally cools air directly or through a refrigerant-based indoor unit. A chiller cools water or another fluid, which is then circulated to equipment or air-conditioning units to provide cooling.

What does TR mean in chiller capacity?

TR stands for ton of refrigeration, a unit used to measure cooling capacity. One TR is approximately 3.517 kW of cooling.

Conclusion

Chillers are essential cooling systems used in commercial buildings, hospitals, manufacturing facilities, data centres, and many industrial processes. They remove heat from water or another fluid and provide controlled cooling for different applications.

The main choices include air-cooled and water-cooled systems, as well as compressor technologies such as scroll, screw, centrifugal, and reciprocating designs. Absorption chillers provide another option when a suitable heat source is available.

Each system has different installation requirements, operating characteristics, maintenance needs, and energy performance. Selecting the right chiller requires careful consideration of cooling load, efficiency, operating environment, refrigerant, infrastructure, and total ownership cost.