Plant Utilities worked example

Cooling Tower Load at 11% approach and fouling allowance: a worked example

Suppose approach and fouling allowance falls to 11%. This page works the full calculation at that level so you can see exactly which result moves and by how much. Estimate cooling tower load coverage time for heat rejection, approach margin, and fouling allowance planning.

The inputs for this scenario

  • Required tower heat rejection time: 300 tower-min (held at the documented default)
  • Tower load coverage rate: 1 tower-min / min (held at the documented default)
  • Approach and fouling allowance: 11 % (the input this scenario stresses; the baseline uses 15)

Working through the calculation

  • The calculation starts from the formula this tool documents: Base cooling tower load time = required tower heat rejection time รท tower load coverage rate.
  • Required cooling tower load time works out to 333 min at these inputs, and this is the headline figure for the scenario.
  • Base cooling tower load time works out to 300 min at these inputs.
  • Allowance applied works out to 11 % at these inputs.
  • Utility coverage rate works out to 1 tower-min / min at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where approach and fouling allowance sits at 15% and the headline result is 345 min, this scenario comes in 3.48% below the baseline at 333 min.
  • It divides the required tower heat-rejection duty by the tower's effective coverage rate, then multiplies by one plus an approach-and-fouling allowance to get realistic runtime. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Required cooling tower load time: 333 min (headline result)
  • Base cooling tower load time: 300 min
  • Allowance applied: 11 %
  • Utility coverage rate: 1 tower-min / min

Run it with your numbers

  • To rerun this with your own numbers, open the live Cooling Tower Load calculator, set approach and fouling allowance to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.