What does chiller mean?
In English, chill is a verb meaning 'to cool'; chiller also literally means 'cooler'. In HVAC, this term describes, using the refrigeration cycle, a water-cooling machine. In Turkish specifications, the same equipment is described as cooling group, water cooling group or chiller group .
The key point that separates a chiller from a split air conditioner is this: a split air conditioner sends refrigerant directly to the indoor unit in the room; a chiller transfers the cooling to water and distributes the water through the building. In large buildings, carrying water in pipes is safer and more controllable than circulating refrigerant through the whole building.
What is a chiller used for, and where is it used?
- Comfort cooling: producing chilled water for fan coils and air handling units in hospitals, shopping malls, hotels, large offices, and public buildings
- Process cooling: cooling of machines, molds, and products in plastic injection, food, pharmaceutical, chemical, and metal industries
- Data centers: feeding chilled-water precision air conditioners (CRAH)
- Heat pump chillers: doing two jobs with one unit by producing chilled water in summer and hot water in winter
How does a chiller cooling system work?
Like other cooling equipment, a chiller works with a four-component refrigeration cycle. The difference is that the cooling is delivered to water instead of air.
01Evaporator: where the water is cooled
Warm water returning from the building (typically around 12 °C in comfort applications) enters the evaporator. There the evaporating refrigerant absorbs the heat of the water, and the water is cooled to about 7 °C and sent back to the building. This '7/12 °C' regime is a common design value; different temperatures can be selected depending on the project. Details: evaporator types.
02Compressor: the heart of the cycle
It compresses the low-pressure gas evaporated in the evaporator, raising its pressure and temperature. Depending on capacity, scroll, screw, or centrifugal compressors are used in chillers.
03Condenser: where heat is rejected
The hot gas gives up its heat in the condenser to the outdoor air (air-cooled) or to cooling tower water (water-cooled) and turns into a liquid. Details: condenser types.
04Expansion valve
It lowers the pressure of the liquid refrigerant and sends it to the evaporator; the cycle starts again.
Beyond the chiller itself, there are other components that complete the system: chilled water pumps, expansion tank, a buffer tank when needed, valves, strainers, and the control system. To get a rough idea of the flow the chiller will produce, you can use the chiller flow and capacity calculator.
Difference between air-cooled and water-cooled chillers
| Air-cooled chiller | Water-cooled chiller | |
|---|---|---|
| Where it rejects heat | Outdoor air, via condenser fans | Cooling tower water |
| Installation location | Usually roof or open area | Enclosed plant room + tower on the roof |
| Additional equipment | Low | Cooling tower, condenser pump, water treatment |
| Efficiency | More affected by outdoor temperature | Usually more efficient at large capacities |
| Maintenance | Condenser coil cleaning | Tower water quality, condenser tube cleaning |
We compared which type suits your building, capacity, and water availability in our air-cooled or water-cooled article.
Chiller compressor types
- Scroll: in small and medium capacities, usually with staged operation using multiple compressors.
- Screw: common in medium and large capacities; the oil system is an important part of maintenance.
- Centrifugal: used in very large capacities, mostly in water-cooled chillers; oil-free types with magnetic bearings also exist.
Besides these, there are also units driven by a heat source (hot water, steam), called absorption chillers, which are preferred in facilities with waste heat. For compressor failures and overhaul, see our compressor overhaul page.
How is chiller efficiency read?
A chiller's efficiency is measured by the cooling it produces relative to the electricity it consumes (EER, COP, kW/TR). Because units run at part load most of the time, seasonal values (IPLV, SEER) describe real consumption better. Details are in our COP and EER article; you can make a preliminary calculation of your own values with the IPLV calculator.
Maintenance or fault support for your chiller
Write the brand, model, and alarm information; we will start with a diagnosis based on measurements.
Why is chiller maintenance important?
A dirty condenser, the wrong refrigerant amount, or low water flow makes a chiller use more electricity and trip on alarms. Regular maintenance includes pressure and temperature measurements, compressor currents, condenser cleaning, and testing of safety devices. For the checklist see our chiller maintenance page, and for the service scope see our chiller service and cooling group service pages.
Frequently asked questions
What does chiller mean?
Chiller means 'cooler' in English. In HVAC it describes the machine that cools water and sends chilled water to a building or a process. In Turkish it is also called a cooling group (soğutma grubu).
What is the difference between a chiller and an air conditioner?
An air conditioner sends refrigerant directly to the indoor unit; a chiller produces chilled water, and this water cools the air in fan coils or air handling units.
What temperature does a chiller cool water to?
In comfort applications the typical design value is 7 °C supply and 12 °C return water. In process and special applications, different temperatures and glycol water can be used.
Is an air-cooled or water-cooled chiller better?
There is no single right answer. Water-cooled chillers are generally more efficient at large capacities but need a cooling tower and water treatment; air-cooled chillers are simpler to install.
Does a chiller heat?
Heat pump chillers can produce hot water in winter by reversing the cycle with a four-way valve. Standard chillers only cool.