Industrial water chillers remove heat from a liquid—usually water or a water-glycol mixture—and reject that heat somewhere else. They are used in factories, food and beverage plants, pharmaceutical production, plastic molding, data centers, laboratories, HVAC systems, laser equipment, machine tools, chemical processes, and many other applications where temperature must be controlled more precisely than ordinary ventilation can provide.
The older version of this article mixed several different ways of classifying chillers. It listed reciprocating, scroll, and screw machines but did not clearly separate compressor type from condenser type. A chiller can be described by both. For example, a unit may be an air-cooled scroll chiller or a water-cooled centrifugal chiller. Those labels answer different questions.
The U.S. Department of Energy currently separates electric chillers into air-cooled and water-cooled categories and further distinguishes positive-displacement and centrifugal water-cooled machines for efficiency requirements. Modern systems may use reciprocating, scroll, screw, centrifugal, or magnetic-bearing centrifugal compressors depending on capacity and application. Absorption chillers form a separate category because they use thermal energy rather than relying primarily on a mechanical compressor.
This guide explains how Water chillers work, the major compressor and condenser types, chilled-water and condenser-water loops, process cooling, glycol and brine, controls, variable-speed operation, efficiency, free cooling, heat recovery, refrigerants, sizing, maintenance, and how to choose the right chiller for an industrial application.
What Is an Industrial Water Chiller?
A water chiller is a refrigeration system that cools a circulating liquid.
The chilled liquid can be sent to:
- air-handling coils;
- process heat exchangers;
- injection molding machines;
- laser equipment;
- reactors;
- food-processing equipment;
- data-center cooling systems.
The Chiller Does Not “Create Cold”
It moves heat.
A typical vapor-compression chiller:
- absorbs heat from chilled water in the evaporator;
- compresses refrigerant vapor;
- rejects heat through the condenser;
- expands the refrigerant to lower its pressure;
- repeats the cycle.
The Four Basic Refrigeration Components
Evaporator
The refrigerant evaporates while absorbing heat from the chilled-water loop.
Compressor
The compressor raises refrigerant pressure and temperature.
Condenser
The refrigerant rejects heat and condenses back to liquid.
Expansion Device
The expansion device reduces pressure before the refrigerant returns to the evaporator.
Two Different Ways to Classify Chillers
By heat rejection
- air cooled;
- water cooled.
By compressor
- reciprocating;
- scroll;
- screw;
- centrifugal.
A proper specification normally includes both.
Air-Cooled Chillers
Air-cooled chillers reject condenser heat directly to outdoor air through:
- condenser coils;
- fans.
They do not need a cooling tower and condenser-water loop.
Advantages of Air-Cooled Chillers
- simpler installation;
- no cooling tower;
- lower water use;
- less water-treatment infrastructure;
- good choice for smaller or medium plants;
- easy packaged installation.
Limitations of Air-Cooled Chillers
- efficiency can fall in hot outdoor weather;
- outdoor fan noise;
- larger condenser footprint;
- exposed coils need cleaning;
- may be less efficient than a well-designed water-cooled plant at large scale.
Water-Cooled Chillers
Water-cooled chillers reject heat to a condenser-water loop.
The condenser water normally flows to a cooling tower, where heat is transferred to the atmosphere.
Major Components of a Water-Cooled Plant
- chiller;
- chilled-water pumps;
- condenser-water pumps;
- cooling tower;
- controls;
- water treatment.
Advantages of Water-Cooled Chillers
- strong efficiency at large capacity;
- stable condenser conditions;
- good fit for large buildings and industrial plants;
- long equipment life when maintained correctly.
Limitations of Water-Cooled Chillers
- cooling tower required;
- water consumption;
- water-treatment requirements;
- more pumps and controls;
- greater mechanical-room complexity.
Cooling Towers
A cooling tower rejects condenser heat primarily through evaporative cooling.
It can cool water toward the outdoor wet-bulb temperature rather than merely the dry-bulb temperature.
Cooling Tower Water Treatment
Water treatment helps control:
- scale;
- corrosion;
- biological growth;
- solids.
Legionella Risk
Cooling towers can aerosolize water droplets and require a proper water-management program to control Legionella risk.
Maintenance should follow:
- local regulations;
- recognized water-management standards;
- manufacturer requirements.
Reciprocating Chillers
Reciprocating compressors use pistons moving inside cylinders.
They were historically common in smaller and medium refrigeration systems.
Advantages
- mature technology;
- repairable compressor architecture;
- good performance in selected applications.
Limitations
- more moving parts;
- vibration;
- maintenance;
- less common in many modern packaged chiller markets than scroll or screw.
Scroll Chillers
A scroll compressor uses two spiral-shaped elements:
- one stationary;
- one orbiting.
The refrigerant is progressively compressed between the scrolls.
Where Scroll Chillers Are Common
They are frequently used for:
- small to medium process loads;
- air-cooled packaged chillers;
- comfort cooling.
Advantages of Scroll Compressors
- compact;
- relatively quiet;
- few moving parts;
- good reliability;
- modular capacity through multiple compressors.
Multiple Scroll Circuits
A packaged chiller may contain several scroll compressors.
Controls can stage them to match load.
Screw Chillers
Screw compressors use rotating helical rotors to compress refrigerant.
They are common in medium to relatively large capacities.
Advantages of Screw Chillers
- continuous rotary compression;
- good part-load capability;
- fewer reciprocating components;
- high capacity in a compact package.
Variable-Speed Screw Chillers
A variable-frequency drive can adjust compressor speed to match load and operating conditions.
This may improve part-load efficiency significantly.
Oil Management
Traditional screw compressors require careful:
- oil separation;
- oil return;
- lubrication.
Maintenance problems can affect:
- capacity;
- heat transfer;
- compressor life.
Centrifugal Chillers
Centrifugal compressors use a high-speed impeller to impart velocity to refrigerant and convert that energy into pressure.
They are commonly used in larger cooling plants.
Advantages of Centrifugal Chillers
- high capacity;
- excellent full- and part-load efficiency in suitable systems;
- compact compressor relative to capacity;
- low vibration compared with reciprocating machines.
Surge
Centrifugal compressors have an operating limit called surge.
Controls must keep the compressor within a stable operating envelope.
Magnetic-Bearing Centrifugal Chillers
Some modern centrifugal compressors use magnetic bearings instead of conventional oil-lubricated bearings.
Potential benefits include:
- oil-free refrigerant circuit;
- low mechanical friction;
- strong part-load efficiency;
- reduced bearing wear.
Oil-Free Does Not Mean Maintenance-Free
The system still requires:
- electrical inspection;
- heat-exchanger cleaning;
- controls maintenance;
- refrigerant management.
Absorption Chillers
Absorption chillers use heat as the primary driving energy rather than a conventional mechanical compressor.
Common heat sources include:
- steam;
- hot water;
- waste heat;
- direct-fired fuel.
Lithium Bromide Absorption
Many comfort-cooling absorption chillers use:
- water as refrigerant;
- lithium bromide as absorbent.
Why Use Absorption?
It can be attractive when:
- waste heat is available;
- steam is inexpensive;
- electrical demand needs reduction;
- combined heat and power is present.
Absorption Limitations
- larger equipment;
- lower coefficient of performance than many electric chillers;
- vacuum maintenance;
- water chemistry/crystallization concerns.
Process Chillers vs. HVAC Chillers
HVAC chillers usually support building comfort.
Process chillers control industrial equipment or product temperature.
Process requirements may include:
- 24/7 operation;
- tight temperature control;
- low fluid temperature;
- dirty industrial environment;
- redundancy.
Food and Beverage
Chillers can support:
- fermentation temperature;
- milk cooling;
- brewery processes;
- ingredient cooling;
- packaging.
Pharmaceutical Manufacturing
Applications include:
- reactor jacket cooling;
- cleanroom HVAC;
- process temperature control;
- laboratory equipment.
Plastics
Injection molding and extrusion generate substantial heat.
Chillers cool:
- molds;
- hydraulic oil;
- extrusion equipment.
Stable mold temperature can influence:
- cycle time;
- part dimensions;
- surface quality.
Laser and Machine Tool Cooling
Precision equipment may require tight coolant temperature to maintain:
- optical stability;
- dimensional accuracy;
- spindle life.
Data Centers
Large data centers may use:
- chilled water;
- air-cooled chillers;
- water-cooled plants;
- economizer/free cooling;
- liquid cooling heat exchangers.
The Chilled-Water Loop
A basic loop includes:
- chiller evaporator;
- pump;
- cooling load;
- return piping.
Water leaves the chiller cold, absorbs heat, and returns warmer.
Supply and Return Temperatures
Typical HVAC values are application-specific.
Industrial processes may require:
- much colder water;
- higher temperature water;
- very narrow control bands.
Do not design a process plant from a generic 44°F supply-water assumption.
Temperature Difference
The difference between return and supply temperature determines how much heat a given flow can carry.
For water:
Cooling load is proportional to flow × temperature difference.
Low Delta-T Syndrome
In large chilled-water plants, unexpectedly low return-water temperature difference can require excessive flow and reduce system performance.
Causes can include:
- control-valve problems;
- coil bypass;
- overpumping;
- poor load control.
Primary-Secondary Pumping
Traditional central plants may use:
- primary chiller pumps;
- secondary distribution pumps.
Variable Primary Flow
Modern plants may use variable primary flow when chillers and controls support it.
This can reduce pumping energy.
Glycol
Ethylene glycol or propylene glycol can be mixed with water to:
- lower freezing point;
- protect outdoor piping;
- support subfreezing process temperatures.
Glycol Reduces Heat-Transfer Performance
Compared with pure water, glycol mixtures generally have:
- lower specific heat;
- higher viscosity.
This affects:
- pump power;
- flow;
- heat exchanger sizing.
Ethylene vs. Propylene Glycol
Ethylene glycol has strong thermophysical performance but is toxic if ingested.
Propylene glycol is often chosen where lower toxicity is required, such as selected food-related applications.
Use an appropriate inhibited industrial formulation.
Brine Systems
Very low-temperature systems may use:
- glycol;
- salt brines;
- special heat-transfer fluids.
Corrosion compatibility becomes critical.
Chiller Capacity
Cooling capacity is often expressed in:
- kW;
- tons of refrigeration.
One refrigeration ton is approximately:
3.517 kW of cooling.
Do Not Size From Floor Area Alone
Industrial chiller sizing should use a heat-load calculation.
Include:
- process heat;
- motors;
- product load;
- ambient heat gain;
- future capacity;
- simultaneous load.
Oversizing Is Not Harmless
An oversized chiller can:
- cycle excessively;
- operate inefficiently;
- cost more;
- control poorly at low load.
Undersizing
An undersized unit can:
- run continuously;
- fail to maintain temperature;
- limit production.
Redundancy
Critical processes may use:
- N+1 chillers;
- multiple modules;
- standby pumps.
Modular Chillers
Several smaller chiller modules can provide:
- staging;
- redundancy;
- incremental expansion.
Efficiency
Chiller efficiency can be expressed as:
- kW/ton;
- COP;
- EER;
- IPLV/NPLV depending standard/context.
Full Load vs. Part Load
Most comfort-cooling chillers operate at part load much of the year.
The DOE specifically distinguishes full-load and part-load optimized chiller requirements.
IPLV
Integrated Part Load Value estimates performance across several operating points.
It is useful for comparison but does not exactly reproduce every real plant’s:
- weather;
- load profile;
- temperatures.
Variable-Speed Drives
VFDs can improve efficiency for:
- compressors;
- pumps;
- cooling-tower fans.
Control sequence matters as much as installing the drive.
Condenser Temperature
Lower condensing temperature generally reduces compressor work.
But equipment must remain within manufacturer operating limits.
Chilled-Water Reset
If the process can tolerate warmer chilled water at low load, raising supply-water setpoint can improve efficiency.
Do not use this strategy where product temperature must remain fixed.
Free Cooling
Economizer or free-cooling systems use favorable outdoor conditions to reduce compressor operation.
Types include:
- waterside economizer;
- air-cooled integrated free-cooling coils.
Where Free Cooling Works Best
It is most attractive when:
- outdoor temperatures are low;
- process cooling is needed year-round;
- chilled-water temperature is relatively high.
Heat Recovery
Instead of rejecting all condenser heat outdoors, a heat-recovery chiller can provide useful hot water.
Potential uses:
- domestic hot water;
- process preheating;
- reheat;
- space heating.
Simultaneous Heating and Cooling
Facilities with year-round cooling and heating loads may gain substantial efficiency from heat recovery.
Refrigerants
Refrigerant choice is changing because of:
- global-warming-potential regulations;
- efficiency;
- safety classifications;
- availability.
Do Not Choose a Chiller Only by Refrigerant Name
Evaluate:
- regulatory phase-down;
- flammability;
- toxicity;
- service availability;
- equipment efficiency.
Leak Detection
Mechanical rooms may require:
- refrigerant detectors;
- ventilation;
- alarms;
- code-required safety measures.
Controls
Modern chiller controls monitor:
- temperatures;
- pressures;
- flow;
- compressor load;
- alarms;
- energy.
Building/Plant Automation
Chillers can integrate through protocols such as:
- BACnet;
- Modbus;
- other industrial protocols.
Plant Sequencing
In multi-chiller systems, controls decide:
- which chiller runs;
- when another starts;
- pump speed;
- tower fan speed.
Poor sequencing can waste more energy than differences between two efficient chillers.
Water Quality
Closed chilled-water loops need control of:
- corrosion;
- microbial growth;
- scale;
- oxygen ingress.
Dirty Heat Exchangers
Fouling increases the temperature difference needed for heat transfer and can reduce:
- capacity;
- efficiency.
Strainers
Strainers protect heat exchangers from debris.
Monitor pressure drop and clean as needed.
Flow Switches
Chillers require adequate evaporator and condenser flow.
Low flow can cause:
- freeze risk;
- high pressure;
- shutdown.
Evaporator Freeze Protection
Protection strategies include:
- flow interlock;
- low-temperature cutout;
- glycol;
- heater;
- continuous circulation.
Maintenance for Air-Cooled Units
Typical tasks:
- clean condenser coils;
- inspect fans;
- check refrigerant charge;
- inspect electrical connections;
- review alarms.
Maintenance for Water-Cooled Units
Additional tasks:
- tube cleaning;
- cooling-tower maintenance;
- water treatment;
- pump inspection.
Predictive Maintenance
Large chiller plants can monitor:
- approach temperature;
- compressor vibration;
- motor current;
- refrigerant pressures;
- oil condition.
Trend analysis can identify deterioration before failure.
Chiller Approach Temperature
Approach is the difference between:
- leaving fluid temperature;
- refrigerant saturation temperature
at a heat exchanger.
Rising approach can indicate:
- fouling;
- flow problem;
- refrigerant issue.
Noise
Outdoor air-cooled chillers can be a major noise source.
Consider:
- night operation;
- neighbors;
- acoustic barriers;
- fan speed.
Location
Maintain sufficient clearance for:
- airflow;
- tube removal;
- service access;
- replacement.
Do Not Trap Air-Cooled Chillers in a Hot Courtyard
Recirculation of discharge air can:
- raise condensing temperature;
- reduce capacity;
- increase energy use.
Choosing the Correct Chiller
Ask:
- What is the peak cooling load?
- What is the minimum load?
- Required supply temperature?
- Water or glycol?
- 24/7 or intermittent?
- Outdoor climate?
- Water availability?
- Redundancy requirement?
- Space/noise limits?
- Energy cost?
Air-Cooled vs. Water-Cooled Selection
Air cooled can be attractive where:
- water is scarce;
- simplicity matters;
- capacity is modest.
Water cooled can be attractive where:
- plant is large;
- high annual run hours;
- efficiency justifies tower complexity.
Compressor Selection
Scroll:
- small/medium;
- modular.
Screw:
- medium/large;
- industrial process.
Centrifugal:
- large central plants;
- high efficiency.
Total Cost of Ownership
Compare:
- purchase;
- installation;
- electricity;
- water;
- maintenance;
- refrigerant;
- expected life.
Lowest Purchase Price Can Be Expensive
A chiller operating thousands of hours annually can consume many times its purchase cost in energy over its life.
Useful DOE Resource
Final Thoughts
Industrial water chillers should be classified by both the way they reject heat and the compressor technology they use. Air-cooled and water-cooled describe the condenser side; reciprocating, scroll, screw, and centrifugal describe the compressor. Absorption machines form another category driven primarily by heat.
The best chiller is not simply the one with the highest nominal efficiency. It must match the process load profile, required fluid temperature, ambient conditions, water availability, redundancy needs, refrigerant regulations, and plant controls.
For a reliable installation, calculate the actual process heat load, account for part-load operation, size pumps and heat exchangers correctly, maintain water quality, and measure system performance after commissioning. In many industrial plants, optimizing the complete chiller system—not just buying a new machine—creates the largest energy and reliability improvement.