Cooling Tower Handbook -

Watch the fan exhaust. A healthy winter plume is wispy and dissipates quickly. A dangerous plume is thick, heavy, and drifts horizontally without rising. This indicates the water is entering the cold air basin at a temperature too low to melt the ice forming upstream.

Here it is, the line you should memorize and stencil onto the tower control panel: cooling tower handbook

When ice forms, panic leads to silence. Silence leads to stagnation. Stagnation leads to a tower that looks less like a heat exchanger and more like a frozen waterfall. A frozen cooling tower cannot be thawed with steam hoses; it must be rebuilt in April. Watch the fan exhaust

Respect the cold. Your tower will thank you in July. This indicates the water is entering the cold

Ice formation begins not at the bottom basin, but at the air inlets—specifically on the louvers and fill. As falling water droplets drift into the sub-freezing air stream, they flash into ice crystals that adhere to the leading edges of the fill. This is called accretion . If left unchecked, an ice bridge will form across the air intake, strangling airflow, collapsing the fill, and ultimately toppling the fan deck.

If you see ice, do not shut down. Increase heat load. Increase water flow. Do not stop the fan unless you intend to scrap the cell.

From the Cooling Tower Handbook, 4th Edition