Plant Utilities worked example

Cooling Tower Load at 17% approach and fouling allowance: a worked example

What does the result look like when approach and fouling allowance reaches 17%? The full calculation is worked below with real intermediate numbers. Use it when reviewing cooling tower load for a utility budget, maintenance priority, capacity check, energy project, or production support plan.

The inputs for this scenario

  • Required tower heat rejection time: 300 tower-min (unchanged)
  • Tower load coverage rate: 1 tower-min / min (unchanged)
  • Approach and fouling allowance: 17 % (raised for this scenario; the documented default is 15)

Working through the calculation

  • Applying the documented formula (Base cooling tower load time = required tower heat rejection time รท tower load coverage rate) to the inputs above produces each figure below.
  • At this operating point the engine returns 351 min for required cooling tower load time, the number this scenario is built around.
  • At this operating point the engine returns 300 min for base cooling tower load time.
  • At this operating point the engine returns 17 % for allowance applied.
  • At this operating point the engine returns 1 tower-min / min for utility coverage rate.

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 1.74% above the baseline at 351 min.
  • A figure at this level is achievable when approach and fouling allowance is genuinely sustained, not just peaked for a shift. It assumes a steady coverage rate and a single lumped allowance; it does not model wet-bulb swings, variable-speed fan turndown, or transient load spikes, so treat the result as a planning figure, not a thermal design.

Results at a glance

  • Required cooling tower load time: 351 min (headline result)
  • Base cooling tower load time: 300 min
  • Allowance applied: 17 %
  • Utility coverage rate: 1 tower-min / min

Run it with your numbers

  • Every input above is editable in the live Cooling Tower Load calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.