What Is A Chiller And How Does It Work?

A chiller is a refrigeration system that removes heat from a liquid (typically water or glycol) and rejects that heat to the environment — either to outdoor air (air-cooled) or to water (water-cooled). The chilled liquid is then circulated through a building or process system to absorb heat at the point where cooling is needed. Chillers are the primary cooling equipment in commercial buildings, industrial processes, data centers, food production, and a wide range of other applications.

The Basic Refrigeration Cycle

All mechanical chillers operate on the vapor-compression refrigeration cycle, with four main components working in sequence:

• Evaporator: warm chilled water or process fluid enters the evaporator. Refrigerant at low pressure absorbs heat from this fluid, evaporating in the process. The fluid exits cooled; the refrigerant exits as a low-pressure vapor.
• Compressor: the compressor raises the refrigerant vapor to high pressure, which simultaneously raises its temperature. This is the component that requires the most energy — and where most of the chiller's electrical consumption occurs.
• Condenser: the hot, high-pressure refrigerant vapor flows to the condenser. In an air-cooled chiller, outdoor air passes over condenser coils to absorb heat from the refrigerant. In a water-cooled chiller, water from a cooling tower absorbs the heat. The refrigerant condenses from vapor to liquid.
• Expansion device: the high-pressure liquid refrigerant passes through an expansion valve, which drops its pressure and temperature. The cold, low-pressure refrigerant then returns to the evaporator to absorb heat again and repeat the cycle.

> A simple way to think about it: the refrigerant picks up heat from your process or building (at the evaporator), carries it to the condenser, and releases it to the outdoor air or cooling water. The compressor drives this heat transfer from low temperature to high temperature — which is work that requires electricity.

Air-Cooled vs. Water-Cooled Chillers

Air-Cooled	Water-Cooled
Rejects heat to outdoor air through condenser coils and fans	Rejects heat to water, which flows to a cooling tower
Self-contained — no cooling tower required	Requires a cooling tower and associated water treatment
Lower installation cost; simpler system	Higher installation cost; more infrastructure
Efficiency decreases on hot days (when you need it most)	More consistent efficiency; less sensitive to outdoor air temperature
Standard for most commercial and industrial applications up to several hundred tons	Preferred for very large systems (hundreds to thousands of tons)
No water consumption for heat rejection	Cooling tower evaporates water for heat rejection

What Chillers Cool

Most commercial and industrial applications use chillers to cool a circulating fluid (chilled water or glycol) rather than directly cooling air or product. This fluid circulates to where cooling is needed:

• In commercial HVAC: chilled water circulates to air handlers and fan coil units that cool building air
• In process cooling: chilled glycol or water circulates to jacketed vessels, heat exchangers, laser heads, molds, or other process equipment
• In food processing: chilled glycol circulates to fermenters, cooling tunnels, immersion chillers, and cold room air handlers
• In data centers: chilled water circulates to CRAC/CRAH air units or to CDUs for rack-level liquid cooling

Frequently Asked Questions

What is the difference between a chiller and a heat pump?

A chiller is designed to cool — it moves heat from where you don't want it to somewhere you can reject it (outdoor air or water). A heat pump operates on the same refrigeration cycle but is designed to provide heating — it moves heat from a low-temperature source (outdoor air or ground) to a higher-temperature space. Many heat pumps can reverse to provide cooling in summer. Commercial chillers are typically optimized for cooling only.

How long do commercial chillers last?

Well-maintained commercial chillers have a service life of 20-30 years. Oil-free magnetic bearing compressors (such as Danfoss TurboCor) may extend service life beyond oil-lubricated compressors due to the absence of mechanical wear from oil system components. Maintenance quality is the primary determinant of service life in most cases.

> Talk with G&D's team about chiller selection for your application -> Contact us