Cooling Tower Calculator

This cooling tower calculator computes heat rejection, range, approach, and the full water balance from operating conditions. Enter the hot and cold water temperatures, entering wet-bulb temperature, circulating flow, cycles of concentration, drift loss, and the evaporation rate; the tool returns cooling range, approach, heat rejected in MBH, nominal tower tons and tons of heat, and the evaporation, drift, blowdown, and total make-up flows in GPM.

It also screens for common operating concerns — a tight approach below 5°F, an impossible approach at or below the wet-bulb, a leaving water temperature above 95°F, and water in the Legionella growth band — and reminds you that every open tower needs a water management program.

Heat rejected is the water-side heat balance with the standard 500 constant (8.33 lb/gal × 60 min/hr × 1.0 BTU/lb·°F). Towers are catalogued in nominal tower tons of 15,000 BTU/hr — 3 GPM cooled from 95°F to 85°F at 78°F wet-bulb — roughly one ton of chiller cooling plus its compressor heat; the 12,000 BTU/hr figure is shown too because it is easy to confuse the two. Evaporation defaults to 1.0% of circulating flow per 10°F of range, which treats all rejected heat as latent (c_p × range ÷ h_fg, h_fg ≈ 1,000 BTU/lb) — the AIM Works app’s basis; in typical summer conditions part of the heat leaves as sensible heat and about 0.85% is common, so enter that if you prefer. Drift leaves as circulating water and carries dissolved solids out, so it reduces the bleed needed: blowdown = evaporation ÷ (cycles − 1) − drift. Rules of thumb only — use the tower manufacturer’s selection for final design.