Adopting free cooling
Free cooling adoption is the addition of a means to reject process or building heat directly to cool ambient air or water when conditions allow, so mechanical chillers can be unloaded or switched off. It exploits the hours when outdoor conditions are cold enough to do the cooling that compressors would otherwise do.
What it is
When the ambient wet-bulb or dry-bulb temperature is well below the required chilled-water temperature, heat can be rejected without running the chiller's compressors — through a cooling tower, dry cooler or a heat exchanger that lets the cooling medium cool the loop directly. Free cooling is the equipment and control logic that switches into this mode automatically whenever the weather permits, and back to mechanical cooling when it does not.
Why it is done
Compressors are the largest energy user in a cooling plant, and for many hours of the year — especially overnight and in winter — the ambient is cold enough to provide cooling for the cost of pumps and fans alone. Without free cooling, those compressors run needlessly. Adding it captures cooling energy that the climate offers for free, with the saving largest in cool climates and for loops that tolerate a higher supply temperature.
How it is done
The cooling load profile and the achievable supply temperature are mapped against local ambient conditions to estimate the free-cooling hours available. The appropriate route is selected — integrated cooling-tower free cooling via a plate heat exchanger, or dry coolers for water-short sites. Changeover controls are configured with sensible setpoints and hysteresis so the plant switches modes on ambient and load without hunting, and partial free cooling is enabled where the ambient can carry only part of the load. Performance is then verified by comparing chiller energy in free-cooling hours against the baseline.
- Map load vs ambient
- Estimate free-cooling hours
- Select cooling route
- Configure changeover control
- Enable partial mode
- Verify chiller savings
What to watch for
Setting the changeover band too tight makes the plant flip between free and mechanical cooling repeatedly, while too wide a band leaves free-cooling hours unused. Designing for full free cooling only, with no partial mode, throws away the many hours when ambient can carry part of the load. A loop run at an unnecessarily low supply temperature shrinks the free-cooling window that a small reset could have widened.
Related practices
Running a compressed-air leak survey programme
Retrofitting waste-heat recovery
Retrofitting variable-speed drives
Related topics
Cooling Tower Efficiency and Reliability · Setpoint · Specific Energy Consumption (SEC) · Demand Response
Common in: Food Processing · Pharmaceuticals · Chemicals · Dairy