Plant Utilities worked example

Cooling Load Variation at 18% weather and production allowance: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop weather and production allowance to 18%, then walk the calculation through step by step. Estimate cooling recovery time for load swings caused by weather, production changes, batch pull-downs, or fouled exchangers.

The inputs for this scenario

  • Extra cooling load to remove: 240 cooling-min (held at the documented default)
  • Chiller recovery rate: 1 cooling-min / min (held at the documented default)
  • Weather and production allowance: 18 % (the input this scenario stresses; the baseline uses 25)

Working through the calculation

  • The calculation starts from the formula this tool documents: Base cooling load variation time = extra cooling load minutes รท recovery rate.
  • Required cooling load variation time works out to 283 min at these inputs, and this is the headline figure for the scenario.
  • Base cooling load variation time works out to 240 min at these inputs.
  • Allowance applied works out to 18 % at these inputs.
  • Utility coverage rate works out to 1 cooling-min / min at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where weather and production allowance sits at 25% and the headline result is 300 min, this scenario comes in 5.6% below the baseline at 283 min.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to weather and production allowance, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes a constant recovery rate; real chillers lose capacity as condensing temperature rises on hot days, so the allowance must cover that non-linearity rather than the model itself.

Results at a glance

  • Required cooling load variation time: 283 min (headline result)
  • Base cooling load variation time: 240 min
  • Allowance applied: 18 %
  • Utility coverage rate: 1 cooling-min / min

Run it with your numbers

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

Last reviewed 2026-05-12.