Chillers play an important role in commercial buildings, industrial facilities, manufacturing plants, hospitals, data centers, and many other environments where temperature control is necessary. These systems remove heat from water or another circulating fluid and transfer it to the surrounding environment. The cooled fluid can then be used for air conditioning, equipment cooling, or industrial processes. Different chiller systems are designed for different cooling requirements. Some are suitable for small commercial buildings, while others can support large factories and central cooling plants. Their performance depends on factors such as cooling capacity, compressor technology, heat-rejection method, energy consumption, operating conditions, and maintenance needs.
What Is a Chiller?
A chiller is a refrigeration machine that removes heat from a liquid, usually water or a water-glycol mixture. The cooled liquid circulates through pipes to air-handling units, fan-coil units, industrial machines, or process equipment.
Unlike a conventional room air conditioner that cools air directly, a chilled-water system uses liquid to carry cooling energy from one location to another.
For example, in a commercial office building, a chiller cools water and sends it to air-handling units. These units use coils to transfer heat from indoor air to the chilled water. The water becomes warmer as it absorbs heat and returns to the chiller to be cooled again.
In an industrial plant, the same basic principle may be used to maintain the temperature of plastic molding machines, production equipment, chemical processes, or other heat-generating systems.
How Does a Chiller Work?
Most conventional chillers use a vapor-compression refrigeration cycle. This process transfers heat from the chilled liquid to the outside environment.
The main stages are:
Evaporation: The refrigerant absorbs heat from the water or process fluid in the evaporator. As it absorbs heat, the refrigerant changes from liquid to vapor.
Compression: The compressor raises the refrigerant vapor's pressure and temperature.
Condensation: The refrigerant releases heat through a condenser and changes back into a liquid.
Expansion: An expansion device reduces the refrigerant's pressure and temperature before it returns to the evaporator.
The cycle repeats continuously while the system is operating.
Absorption chillers work differently. Instead of relying mainly on a mechanical compressor, they use heat and an absorbent-refrigerant process to produce cooling.
The exact design depends on the chiller type, refrigerant, cooling capacity, and application.
Main Ways to Classify Chillers
Chillers can be grouped according to how they reject heat, how they compress or circulate refrigerant, and the type of energy they use.
Two common classification methods are:
Heat-rejection method: Air-cooled or water-cooled.
Operating technology: Scroll, screw, centrifugal, reciprocating, or absorption.
These categories are not interchangeable. For example, a screw chiller may be either air-cooled or water-cooled. Selecting a chiller therefore involves considering both its operating technology and its heat-rejection method.
1. Air-Cooled Chillers
Air-cooled chillers remove heat by passing outdoor air across condenser coils. Fans move air through the coils, allowing the refrigerant to release the heat collected from the chilled liquid.
These systems generally do not require a separate cooling tower. This can simplify installation and reduce the number of major components in the cooling plant.
How Air-Cooled Chillers Work
The chiller absorbs heat from the circulating liquid in its evaporator. The compressor raises the refrigerant pressure, and the refrigerant then releases heat through an outdoor condenser coil. Fans help carry that heat away.
The cooled liquid returns to the building or industrial process, and the cycle continues.
Advantages
No separate cooling tower is normally required.
Installation can be simpler than a comparable water-cooled system.
Water consumption associated with cooling-tower operation is avoided.
The equipment may be suitable for sites with limited plant-room space.
Maintenance can be more straightforward because there is no condenser-water cooling tower loop.
Limitations
Air-cooled chillers depend on outdoor air temperature. When the weather is very hot, the system may need to work harder to reject heat. This can reduce cooling capacity or increase energy consumption, depending on the equipment and operating conditions.
Fans also require electrical power and can create noise. Outdoor airflow and adequate clearance around the condenser are important for proper performance.
Common Applications
Air-cooled chillers are often used in office buildings, retail spaces, hotels, smaller industrial facilities, laboratories, and sites where water availability or cooling-tower installation is a concern.
2. Water-Cooled Chillers
Water-cooled chillers transfer heat from the refrigerant to condenser water. The warmed condenser water usually travels to a cooling tower, where heat is released to the atmosphere.
These systems can offer high energy efficiency, particularly in larger installations. However, their total performance depends on the chiller, cooling tower, pumps, water treatment, and control system working together.
How Water-Cooled Chillers Work
The evaporator absorbs heat from the chilled-water loop. After compression, the refrigerant releases heat to condenser water in the condenser. The warmed condenser water travels to the cooling tower, where heat is rejected through a combination of air movement and evaporation.
The cooled condenser water then returns to the chiller.
Advantages
Can provide strong energy efficiency for large cooling loads.
Often suitable for central cooling plants operating for long periods.
Can support large commercial and industrial installations.
May perform well in systems with carefully designed cooling towers and controls.
Limitations
Water-cooled systems generally need more equipment and infrastructure than air-cooled systems. This may include a cooling tower, condenser-water pumps, water-treatment equipment, piping, and additional plant space.
Cooling-tower water must be managed to control scale, corrosion, and biological growth. Poor water quality or inadequate maintenance can reduce heat transfer and increase operating costs.
Common Applications
Water-cooled chillers are commonly considered for large hospitals, airports, shopping centers, industrial plants, data centers, and major commercial buildings with substantial cooling demand.
Air-Cooled vs. Water-Cooled Chillers
| Feature | Air-cooled chiller | Water-cooled chiller |
|---|---|---|
| Heat rejection | Outdoor air | Condenser water, usually with a cooling tower |
| Cooling tower | Usually not required | Usually required |
| Water use | No cooling-tower water consumption | Requires cooling-tower water management |
| Installation | Often simpler | Usually more complex |
| Energy efficiency | Often lower at comparable large-scale operating conditions | Often higher in suitable large installations |
| Maintenance | Outdoor coils, fans, and refrigeration components | Chiller, pumps, cooling tower, and water-treatment system |
| Typical suitability | Small to medium facilities and sites with limited water access | Medium to large facilities with significant cooling demand |
Neither type is automatically the best option for every building. Climate, electricity prices, water availability, equipment capacity, noise restrictions, and maintenance resources should all be considered.
3. Scroll Chillers
Scroll chillers use scroll compressors to compress refrigerant. A scroll compressor contains two spiral-shaped elements. One remains fixed while the other moves in a controlled orbit, trapping and compressing refrigerant as it travels toward the center.
Scroll technology is widely used in smaller and medium-sized cooling systems. Some chillers contain multiple scroll compressors, allowing the equipment to adjust cooling output as demand changes.
Advantages
Relatively simple compressor construction.
Generally smooth and quiet operation.
Multiple compressors can provide staged cooling capacity.
Modular designs can make capacity expansion easier.
Suitable for many commercial and light-industrial applications.
Limitations
Scroll chillers may be less suitable than larger compressor technologies for very high-capacity installations when considered as a single machine. Their actual efficiency depends on compressor staging, operating conditions, and system design.
Common Applications
Scroll chillers are often used in small commercial buildings, clinics, laboratories, retail facilities, small manufacturing operations, and equipment-cooling applications.
4. Screw Chillers
Screw chillers use rotary screw compressors. These compressors typically contain two intermeshing helical rotors that compress refrigerant as it moves through the compressor.
They are commonly used for medium and large cooling loads. Depending on the design, a screw chiller may use an air-cooled or water-cooled condenser.
Advantages
Suitable for a broad range of cooling requirements.
Can provide reliable operation under demanding conditions.
Capacity can often be adjusted to match changing loads.
Available in different configurations for commercial and industrial use.
Can be a practical choice where operating loads vary throughout the day.
Limitations
Screw chillers may require more specialized servicing than smaller packaged systems. Compressor design, lubrication requirements, controls, and the selected refrigerant can affect maintenance needs and operating costs.
Common Applications
Screw chillers are used in manufacturing plants, hotels, hospitals, commercial buildings, food-processing facilities, and industrial process-cooling systems.
They can be useful where a facility needs substantial cooling capacity but does not necessarily require a very large centrifugal chiller.
5. Centrifugal Chillers
Centrifugal chillers use a high-speed impeller to increase refrigerant velocity. The system converts this velocity into pressure, allowing the refrigerant to circulate through the refrigeration cycle.
These chillers are commonly associated with large central cooling plants. Many conventional centrifugal chillers are water-cooled, although specialized designs are available for particular operating requirements.
Advantages
Can deliver high cooling capacity.
Often offers excellent efficiency at suitable design conditions.
Well suited to large buildings with continuous cooling demand.
Advanced controls and variable-speed drives can improve performance under changing loads.
Limitations
Centrifugal chillers require careful selection and control. Some designs can experience unstable operation, known as surge, when operating outside their intended range. Their efficiency also depends on the temperature and pressure conditions under which they operate.
Initial installation costs and engineering requirements can be significant, particularly when the system includes a cooling tower and associated water circuits.
Common Applications
Centrifugal chillers are often used in large commercial complexes, airports, hospitals, universities, district cooling plants, and major industrial facilities.
They are especially worth evaluating when the cooling demand is large enough to justify a central chilled-water plant.
6. Reciprocating Chillers
Reciprocating chillers use piston-based compressors. The pistons move inside cylinders to compress refrigerant, much like the basic mechanism used in many conventional piston compressors.
This technology has been used in refrigeration and air-conditioning equipment for many years. Although other compressor types are common in many modern commercial applications, reciprocating chillers remain relevant in certain existing installations and specialized systems.
Advantages
A well-established compressor design.
Can be suitable for smaller or specialized cooling requirements.
Individual components may be serviceable, depending on the design.
Can be practical where existing equipment and maintenance expertise are already available.
Limitations
Reciprocating compressors have moving parts that experience repeated mechanical motion. Vibration, noise, maintenance requirements, and efficiency at varying loads must be considered.
For new installations, buyers should compare current reciprocating options with scroll, screw, and other technologies rather than assuming one design is always preferable.
Common Applications
Reciprocating chillers may be found in older commercial refrigeration systems, smaller cooling installations, and specialized applications where their design and operating characteristics are appropriate.
7. Absorption Chillers
Absorption chillers use thermal energy rather than relying primarily on a conventional electrically driven refrigerant compressor. They use a refrigerant and an absorbent within a process that produces cooling.
A common design uses water as the refrigerant and lithium bromide as the absorbent. Other absorption systems use different working fluids for specific applications.
How Absorption Chillers Work
The system uses heat to separate the refrigerant from the absorbent. The refrigerant then passes through the stages needed to absorb heat from the chilled liquid. Afterward, it returns to the absorption process, and the cycle repeats.
The heat source may be steam, hot water, direct-fired fuel, or recovered waste heat, depending on the system.
Advantages
Can use recovered heat that would otherwise be wasted.
May reduce demand for electricity used by a large mechanical compressor.
Can fit facilities with suitable heat sources or combined heat-and-power systems.
May be attractive where thermal energy is available at a favorable cost.
Limitations
Absorption chillers often require more space and additional thermal-system equipment. They also need careful control of operating conditions and water chemistry. Their overall energy and cost benefits depend on the heat source, cooling-water requirements, and facility design.
Using a fuel-fired absorption chiller does not automatically reduce total energy costs or emissions. The heat source and the complete system must be evaluated.
Common Applications
Absorption chillers may be used in industrial facilities with recoverable waste heat, large institutional buildings, district cooling systems, and plants with suitable steam or hot-water supplies.
8. Magnetic-Bearing and Oil-Free Centrifugal Chillers
Some modern centrifugal chillers use magnetic bearings to support the compressor shaft without conventional mechanical contact at the bearings. Many designs also avoid the traditional oil-lubrication system used by other compressors.
Reducing mechanical contact can help reduce friction and eliminate certain oil-management tasks. However, the equipment still requires suitable controls, refrigerant management, and specialist servicing.
Advantages
Can provide efficient operation under suitable conditions.
May reduce maintenance associated with conventional oil systems.
Variable-speed operation can help match changing cooling loads.
Can be useful in facilities with long operating hours.
Limitations
These systems can have higher initial costs and may require technicians trained in their specific controls and compressor technology. Buyers should compare certified efficiency data, service support, and total lifecycle cost.
Common Applications
Magnetic-bearing centrifugal chillers may be considered for data centers, hospitals, large commercial buildings, and other facilities where cooling efficiency and reliable operation are important.
9. Modular and Packaged Chillers
Modular and packaged chillers describe equipment configurations rather than one specific compressor technology.
A packaged chiller combines major refrigeration components into a factory-assembled unit. A modular system uses multiple smaller units that can work together to meet the facility's total cooling demand.
These systems may use scroll, screw, or other compressor technologies, depending on their capacity and design.
Advantages
Packaged units can simplify installation.
Modular systems can expand as cooling demand grows.
Multiple units may provide operational flexibility.
A system with several units may continue operating at reduced capacity when one unit is unavailable, if the system is properly designed.
Limitations
The performance of a modular system depends on how units are staged and controlled. More individual units can mean additional piping, electrical connections, and maintenance tasks.
Common Applications
Modular and packaged chillers are used in commercial buildings, manufacturing facilities, laboratories, equipment rooms, and facilities where cooling demand may increase over time.
Comparison of Major Chiller Types
| Chiller type | Main operating principle | Common applications | Important consideration |
|---|---|---|---|
| Air-cooled | Rejects heat to outdoor air | Commercial buildings, smaller industrial sites | Outdoor temperature affects performance |
| Water-cooled | Rejects heat to condenser water | Large buildings and central cooling plants | Requires water-system management |
| Scroll | Compresses refrigerant using spiral elements | Small to medium cooling loads | Modular capacity and compressor staging |
| Screw | Compresses refrigerant with helical rotors | Medium to large cooling loads | Load profile and service requirements |
| Centrifugal | Uses a high-speed impeller | Large central cooling plants | Performance at the intended operating conditions |
| Reciprocating | Uses piston movement | Existing or specialized systems | Mechanical maintenance and efficiency |
| Absorption | Uses thermal energy and an absorbent-refrigerant cycle | Facilities with suitable heat sources | Cost and availability of thermal energy |
| Magnetic-bearing centrifugal | Uses magnetic bearings to support a high-speed shaft | Large facilities with long cooling hours | Specialized controls and service support |
| Modular or packaged | Combines one or more refrigeration units | Commercial and industrial facilities | System controls and redundancy |
These categories overlap. For example, a packaged chiller can be air-cooled and use scroll compressors. A water-cooled central plant can use screw or centrifugal chillers.
Common Applications of Chiller Systems
Chillers are used wherever controlled liquid cooling is required. The exact system depends on the amount of heat that must be removed, the required temperature, and the operating environment.
Commercial Buildings
Office buildings, hotels, malls, and large public facilities may use chillers to supply chilled water to air-handling units and fan-coil units. Centralized cooling can serve multiple floors and zones from one plant.
Hospitals and Healthcare Facilities
Hospitals use cooling systems to maintain indoor comfort and support temperature-sensitive equipment and selected clinical or laboratory processes. Critical facilities may require backup capacity and carefully planned maintenance.
Manufacturing and Industrial Processing
Manufacturing equipment can generate substantial heat during operation. Chillers may help control the temperature of plastic molding machines, laser systems, metalworking equipment, and other industrial processes.
Food and Beverage Production
Chilled water or other temperature-controlled fluids can support food processing, beverage production, and equipment cooling. Applications involving food safety or refrigeration require equipment designed for the relevant temperature and hygiene conditions.
Data Centers
Servers and networking equipment generate heat continuously. Chillers can support cooling systems that remove heat from server rooms or liquid-cooling circuits. System design must account for reliability, changing IT loads, energy consumption, and backup arrangements.
Pharmaceutical and Laboratory Facilities
Certain pharmaceutical processes, laboratories, and testing facilities need controlled temperatures for equipment or production processes. Chiller selection should account for the process temperature, stability requirements, and applicable facility standards.
How to Choose the Right Chiller
Selecting a chiller requires more than comparing purchase prices or choosing the largest available unit. A properly selected system should meet the cooling load while controlling energy use and maintaining reliable operation.
1. Calculate the Cooling Load
Cooling load refers to the amount of heat that the system must remove under specified operating conditions.
The load may depend on machinery heat, building occupancy, lighting, outdoor temperature, production schedules, and process requirements. An undersized chiller may struggle to maintain the required temperature. An oversized unit may cost more than necessary and can operate inefficiently if its controls are unsuitable for low loads.
A qualified HVAC or refrigeration engineer can calculate the load using the facility's operating data.
2. Identify the Required Fluid Temperature
Some air-conditioning systems use chilled water at temperatures around 6–7°C under common design conditions. Industrial processes may require warmer or colder fluid, depending on the equipment and production needs.
The required supply and return temperatures influence chiller capacity, energy use, and the type of heat exchanger required.
3. Compare Energy Efficiency
Common measures include:
COP (Coefficient of Performance): Cooling output divided by the energy input under stated conditions. A higher value generally indicates better efficiency.
kW per ton of refrigeration: Electrical input required for each unit of cooling capacity. A lower value generally indicates better efficiency.
IPLV or NPLV: Part-load efficiency measures that help compare performance across a range of operating conditions.
Always compare ratings measured under equivalent conditions. For water-cooled systems, consider the energy used by pumps and cooling towers as well as the chiller itself.
4. Evaluate Climate and Water Availability
Air-cooled systems may be suitable where water is scarce or cooling-tower installation is impractical. Water-cooled systems may offer better efficiency for certain large installations but require water infrastructure and ongoing treatment.
Local weather conditions, water quality, and environmental restrictions can affect the final decision.
5. Consider Maintenance and Reliability
Review the availability of trained technicians, spare parts, manufacturer support, and routine maintenance services.
Facilities that cannot tolerate interruptions may need multiple chillers, backup pumps, or other redundancy measures. Redundancy should be designed around the consequences of equipment failure rather than added without a clear purpose.
6. Compare Total Cost of Ownership
The purchase price is only one part of a chiller's cost. Other expenses include installation, electricity, water, maintenance, refrigerant management, and eventual replacement.
A system with a higher initial price may be economical over time if it operates efficiently and suits the actual cooling load. A lifecycle-cost comparison can help estimate the difference.
Chiller Maintenance and Operating Considerations
Routine maintenance helps a chiller maintain its intended performance and reduces the likelihood of unexpected downtime.
Important tasks may include:
Inspecting refrigerant circuits for leaks and abnormal operating conditions.
Cleaning air-cooled condenser coils and checking fan operation.
Inspecting evaporators, condensers, pumps, valves, and piping.
Monitoring water quality and treating cooling-tower water where applicable.
Checking sensors, control settings, alarms, and electrical connections.
Reviewing operating temperatures, pressure readings, and energy consumption.
Following manufacturer instructions for lubrication, servicing, and component replacement.
The maintenance schedule should match the equipment design and operating environment. Refrigerant handling, electrical work, pressure-system servicing, and other specialized tasks should be performed by qualified technicians.
Common Chiller Selection Mistakes
Several avoidable mistakes can affect the long-term performance of a cooling system.
Choosing equipment based only on capacity: The chiller must match the real load and required temperatures, not just a general building size estimate.
Ignoring part-load performance: Many chillers spend much of their operating time below full capacity. Part-load efficiency and control behavior can therefore matter greatly.
Overlooking auxiliary energy use: Pumps, cooling-tower fans, and other equipment consume energy. The entire cooling plant should be evaluated.
Ignoring local conditions: Outdoor temperature, water availability, noise limits, and installation space can change which system is most practical.
Skipping maintenance planning: A chiller may lose performance because of dirty heat exchangers, poor water quality, faulty sensors, or incorrect controls.
Selecting unfamiliar refrigerant technology without service support: Refrigerant choice, safety requirements, availability, and technician training should be checked before purchase.
Frequently Asked Questions
What are the main types of chillers?
The main compressor-based types are scroll, screw, centrifugal, and reciprocating chillers. Absorption chillers use a heat-driven process instead of relying primarily on a mechanical refrigerant compressor. Chillers are also classified as air-cooled or water-cooled according to how they reject heat.
Which chiller is best for a large commercial building?
A water-cooled centrifugal chiller is often considered for large buildings with substantial cooling demand. Screw chillers and air-cooled systems may be more suitable in other circumstances. The best option depends on the load, climate, water availability, operating schedule, and total cost.
What is the difference between an air-cooled and a water-cooled chiller?
An air-cooled chiller releases heat directly to outdoor air through condenser coils and fans. A water-cooled chiller transfers heat to condenser water, which usually releases it through a cooling tower. Water-cooled systems can be more efficient in suitable large installations but require more infrastructure and water management.
Are absorption chillers energy efficient?
Absorption chillers can be useful when suitable waste heat, steam, or other low-cost thermal energy is available. Their overall efficiency and operating cost depend on the heat source, cooling-water requirements, and the complete system design. They are not automatically the lowest-cost choice.
What is a ton of refrigeration?
A ton of refrigeration is a unit of cooling capacity, not the physical weight of the chiller. One refrigeration ton is approximately 3.517 kilowatts of cooling capacity. Engineers use this unit to describe and compare the cooling capacity of refrigeration equipment.
How long can a chiller operate?
A chiller's service life depends on its design, operating conditions, installation quality, maintenance, and component availability. Regular inspections and appropriate maintenance can help preserve performance, but the expected life of a specific unit should be assessed using manufacturer guidance and its operating history.
Can one chiller serve an entire building?
Yes. A central chiller plant can provide chilled water to multiple floors or zones through a network of pumps and pipes. The design must account for the total cooling load, distribution losses, control requirements, and the need for backup capacity.
Conclusion
Chiller systems are available in several configurations, each designed for different cooling demands and operating conditions. Air-cooled chillers can simplify installation where water use or cooling-tower space is a concern. Water-cooled systems can be efficient choices for large cooling plants. Scroll and screw chillers serve many small-to-large applications, while centrifugal chillers are widely used for substantial central cooling loads. Absorption systems may be attractive when suitable thermal energy is available.