Types of chillers explained
Updated 23 October 2026 · SEO Dons Editorial
What counts as a chiller on this page?
A chiller cools a liquid, usually water or a water and glycol mix, which is then piped to air handling units, fan coils or process equipment. The ecodesign rules that apply in Great Britain cover cooling products and high temperature process chillers with a rated cooling capacity not exceeding 2 MW. They define a comfort chiller as one whose condenser releases heat to ambient air, water or ground heat sinks, and which is designed to operate at leaving chilled water temperatures of 2 °C or more. Process chillers serve machines and products instead of people, and the process and glycol chillers guide covers them.
The Energy Technology List (ETL) is the government's list of energy-efficient products, and it puts refrigerated display cabinets in a different category from packaged chillers. This page is about building and process plant, not catering or shop display chillers.
What is the difference between air-cooled and water-cooled chillers?
An air-cooled chiller rejects heat straight to the outdoor air through fans and coils. A water-cooled chiller passes the heat to a condenser water circuit, which is cooled by a cooling tower or a dry cooler. CIBSE Journal notes that cooling towers generally deliver more efficient operation than air-cooled condensers, and that its example water-cooled centrifugal chiller is available for use with cooling towers or dry coolers.
The efficiency gap shows in the legal and voluntary benchmarks. The percentages below are seasonal space cooling efficiency (ηs,c), which is not the same scale as SEER, so read them against each other and see the guide to SEER and efficiency ratings for how to convert.
| Chiller and size | Ecodesign minimum from 1 January 2021 | ETL listing threshold |
|---|---|---|
| Air-cooled, under 400 kW | 161% | 185% |
| Air-cooled, 400 kW and above (ETL to 1,500 kW) | 179% | 205% |
| Water-cooled, under 400 kW | 200% | 244% |
| Water-cooled, 400 kW to under 1,500 kW | 252% | 310% |
| Water-cooled, 1,500 kW and above (ETL to 2,000 kW) | 272% | 338% |
The trade-off is compliance. A cooling tower or evaporative condenser is a notifiable device under the 1992 regulations unless it contains no water exposed to air, and HSE expects measures to control legionella. A dry cooler avoids that, at the cost of warmer condenser water on hot days. The comparison of cooling towers, dry coolers and adiabatic coolers sets out the differences.
Which compressor type suits which job?
The compressor sets the size range and the part-load behaviour. The table shows one manufacturer's published ranges as examples. They are not limits for each technology, and other makers' ranges differ.
| Compressor | Example range (Daikin Applied UK) | Published cooling capacity |
|---|---|---|
| Scroll, air-cooled | EWAT-CZ, small to medium buildings | 16 to 90 kW |
| Scroll, air-cooled | EWAT-B-C | 252 to 1,012 kW |
| Screw, air-cooled | TZ-D inverter screw | 150 to 1,950 kW |
| Screw, water-cooled | EWWD-VZ inverter screw | 449 to 2,074 kW |
| Magnetic-bearing centrifugal, water-cooled | EWWD-DZ | 320 to 2,173 kW |
| Centrifugal, water-cooled | DWSC | 1,050 to 4,500 kW |
Scroll machines dominate the small and medium end, screw machines the middle, and centrifugal machines the large end. CIBSE Journal says centrifugal compressors have long been used at the large-capacity end of the market, beyond about 500 kW. It adds that magnetic bearings remove the need for oil lubrication, along with oil pumps, sumps, heaters, coolers and separators. Magnetic-bearing machines also have a low starting current, which can matter on a constrained electrical supply.
What are heat-pump and simultaneous heating and cooling chillers?
A reverse-cycle chiller can run as a heat pump. The ETL lists air-cooled reverse-cycle comfort chillers that provide both heating and cooling, and air-cooled simultaneous heating and cooling comfort chillers that provide both at the same time, each up to 1,500 kW of cooling. Daikin Applied lists an air-cooled inverter screw heat pump of 247 to 580 kW cooling and 271 to 618 kW heating, with hot water up to 55 °C.
These suit buildings that need heat and cooling in the same season, such as hotels and hospitals. The wider heat pump picture is on the commercial heat pumps page.
Where do free-cooling and absorption chillers fit?
A free-cooling chiller adds a coil that uses cold outdoor air to cool the water without the compressors. The ETL requires an integral free-cooling mechanism to be controlled so as to maximise free cooling for outside air dry-bulb temperatures between 2.0 and 15.0 °C. Daikin Applied lists an air-cooled scroll range with free cooling of 252 to 1,012 kW. How many hours that offers across the UK is set out in the free cooling chillers by UK region guide.
An absorption chiller replaces the electric compressor with a heat-driven cycle. CIBSE says single-stage machines need heat of at least 80 °C, so they suit sites with surplus heat. The absorption chillers guide covers the economics.
How do you choose a chiller type?
- Size the load first. The sizing guide explains the inputs, because compressor type follows capacity.
- Decide the heat rejection route: air-cooled for simplicity, water-cooled with a tower or dry cooler for large steady loads.
- Check the load profile. Year-round loads favour free cooling, and variable loads favour inverter or multi-compressor machines.
- Check plant space, noise limits, structure and electrical supply, including starting current.
- Check refrigerant and F-gas duties, and the water treatment workload for any wet heat rejection.
- Compare against refrigerant-based alternatives such as VRF at your capacity, using the VRF versus chiller comparison.
The cost drivers are on the chiller cost guide. If you want help specifying a chilled water system, the commercial chillers page explains the process, and you can send an enquiry through the site's form.
Sources
Regulations and guidance are revised, so confirm the current text before relying on a figure.
- Commission Regulation (EU) 2016/2281, article 1, legislation.gov.uk, revised 09/01/2017; checked 22 October 2026.
- Commission Regulation (EU) 2016/2281, article 2, legislation.gov.uk, revised 09/01/2017; checked 22 October 2026.
- Commission Regulation (EU) 2016/2281, annex II, legislation.gov.uk, revised 09/01/2017; checked 22 October 2026.
- Packaged Chillers, Energy Technology List, UK Government; checked 22 October 2026.
- Refrigeration equipment, Energy Technology List, UK Government; checked 22 October 2026.
- The Notification of Cooling Towers and Evaporative Condensers Regulations 1992, regulation 2, legislation.gov.uk; checked 22 October 2026.
- Evaporative cooling systems, Health and Safety Executive, updated 2026-01-14; checked 22 October 2026.
- Module 6: The quiet revolution in chillers, CIBSE Journal, posted July 2009; checked 22 October 2026.
- Module 91: High-efficiency waste heat-powered lithium bromide absorption chillers, CIBSE Journal, posted March 2016; checked 22 October 2026.
- EWAT-CZ, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- TZ-D air-cooled screw inverter chillers, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- EWWD-VZ, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- EWWD-DZ, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- DWSC, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- EWFT-B-C, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- EWYD-BZ, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- EWAT-B-C, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
Common questions
What is a commercial chiller?
It is a packaged refrigeration machine that cools water or a water and glycol mix, which is then piped round a building or process. The ETL describes packaged chillers as factory-assembled units designed to cool liquid. This is different from catering and display chillers.
Does a water-cooled chiller always need a cooling tower?
No. The condenser water can be cooled by a cooling tower or by a dry cooler, and the choice changes the water and legionella duties. A dry cooler has no water exposed to air, but gives warmer condenser water on hot days.
Why do the ETL thresholds differ from the legal minimums?
The legal minimums are a floor for products placed on the market. The ETL threshold is higher, because the list is meant to encourage the purchase of higher-efficiency products. Ask for the declared figure rather than assuming either.
Is a magnetic-bearing chiller the same as a centrifugal chiller?
It is a type of centrifugal chiller. The compressor shaft floats on magnetic bearings, so it needs no oil lubrication. Daikin Applied lists such a water-cooled range at 320 to 2,173 kW.
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