How each one rejects heat
A dry cooler moves heat from a closed water or glycol loop to the air through a finned coil. Nothing evaporates and the fluid never touches the air.
An open cooling tower sprays the water over fill and evaporates a small part of it. Evaporation carries the heat away, which is why a tower can cool water close to the wet-bulb temperature.
The approach limit
A dry cooler can only bring the fluid down toward the dry-bulb temperature. The gap between leaving fluid and ambient is the approach. The KUHLWERX rating point, water 104°F in and 95°F out in 77°F air, is an 18°F approach.
If the process needs 85°F water on a 95°F day, air alone cannot do it. That is a tower, an adiabatic dry cooler or refrigeration.
Water, chemicals and freeze risk
A tower uses makeup water, bleeds off blowdown to control dissolved solids, and needs a water treatment program. A dry cooler needs none of it.
With glycol in the loop, a dry cooler can sit outdoors through a freeze without draining down.
Where the adiabatic dry cooler fits
Adiabatic pads or spray wet the inlet air only on the hottest hours. The unit runs dry most of the year and uses water only when ambient climbs past the point where air alone makes the duty.
| Dry cooler | Cooling tower | |
|---|---|---|
| Lowest fluid temperature | Above dry-bulb | Near wet-bulb |
| Water use | None | Makeup and blowdown |
| Water treatment | None | Required |
| Freeze protection | Glycol loop | Basin heat or drain-down |
| Fan energy | Higher | Lower |