Guide
Cooling Tower vs Chiller: What's the Difference?
Cooling towers and chillers are both used for cooling, but they work on completely different principles. This guide explains the difference, when to use each, and how they work together in large HVAC systems.
7 min readUpdated July 2026
The Fundamental Difference
- Chiller: A machine that uses a refrigeration cycle (compressor, condenser, expansion valve, evaporator) to produce chilled water — typically at 6–7°C. The chilled water is circulated through cooling coils in air handling units to cool building air. Chillers actively remove heat using mechanical refrigeration.
- Cooling tower: A device that cools water by evaporation. Warm water from a process or condenser is sprayed through air, and some of it evaporates, cooling the remaining water to near the wet bulb temperature. Cooling towers don't use refrigeration — they use the natural cooling effect of evaporation. Cooling towers produce water at approximately 27–30°C (the 'condenser water' temperature).
Comparison
| Characteristic | Chiller | Cooling Tower |
|---|---|---|
| Cooling method | Mechanical refrigeration (vapour compression) | Evaporative cooling (water + air) |
| Output | Chilled water at 6–7°C | Condenser water at 27–30°C |
| Minimum temperature | Can cool below wet bulb | Can only cool to wet bulb + 3°C |
| Energy consumption | High (compressor power) | Low (fan and pump only) |
| Capital cost | High | Low to moderate |
| Water consumption | None (closed loop) | High (evaporation + blowdown) |
| Maintenance | Refrigeration specialist required | Water treatment and cleaning |
| Legionella risk | None | High (must manage) |
| Size | Compact | Large (requires roof or ground space) |
When to Use Each
The choice depends on the required water temperature and the application:
- Use a chiller when you need cold water (6–7°C) for air conditioning, process cooling, or dehumidification
- Use a cooling tower when you need to reject heat from a process or condenser and the water temperature only needs to be near the wet bulb (27–30°C)
- Use both together in a water-cooled chiller system: the chiller produces cold water, and the cooling tower rejects the chiller's condenser heat to the atmosphere
- Use only a cooling tower for 'free cooling' in mild climates — when the outdoor wet bulb is low enough, the tower can cool water directly without running the chiller
How They Work Together
In a typical large-building HVAC system, the chiller and cooling tower work as a team:
- The chiller produces chilled water (6–7°C) and circulates it to air handling units
- The AHUs use the chilled water to cool building air
- The warm chilled water returns to the chiller evaporator to be re-cooled
- The chiller's condenser rejects heat to condenser water (27–35°C)
- The warm condenser water is pumped to the cooling tower
- The cooling tower cools the condenser water by evaporation (to 27–30°C)
- The cool condenser water returns to the chiller condenser to absorb more heat
Key insight: Water-cooled chillers (with cooling towers) are approximately 20–30% more energy-efficient than air-cooled chillers, because the condenser can reject heat to water at a lower temperature than air. However, they require more maintenance (water treatment, Legionella management) and consume water.