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Plant Engineering Calculator

Updated Sep 18, 2026

Compressed Air Dryer Purge Loss Calculator — CFM, kW & Annual Cost

Quantify desiccant-dryer purge air from inlet flow and purge percentage, then convert lost compressed air into compressor power, annual energy and cost.

Live calculationWorking shownPrivate in browser

Inputs

Results

Purge flow 150.00 CFM
Power penalty 27.00 kW
Annual energy 162000 kWh
Annual cost $16200
More actions

Shared links reopen these inputs. Recent and saved calculations stay in this browser unless you clear site data.

Formula

Qpurge=Qin×purge%; kWloss=Qpurge×specific power/100.

Your calculation, step by step

These steps use the values currently entered above so the result can be checked independently.

  1. 1.Purge fraction = 15.00% ÷ 100 = 0.1500.
  2. 2.Purge flow = 1000.00 CFM × 0.1500 = 150.00 CFM.
  3. 3.Compressor power penalty = 150.00 × 18.000 kW/100 CFM ÷ 100 = 27.000 kW.
  4. 4.Annual purge energy = 27.000 × 6000 = 162000.0 kWh; cost = 162000.0 × $0.1000 = $16200.00.

How to use this calculator

  1. Enter measured or design values using the units shown beside each field.
  2. Review the live results and the substituted calculation steps before using the estimate.
  3. Check the assumptions below, then continue to a related calculator when the next engineering decision needs another model.

Worked example

A 1,000 CFM dryer using 15% purge consumes 150 CFM before translating that loss into compressor kW.

Assumptions and limits

  • Purge percentage is defined here on dryer inlet flow; convert supplier data first if it is stated on a downstream-air basis.
  • Use measured or OEM purge percentage at the actual dryer cycle.
  • Heated, blower-purge and heat-of-compression dryers have different purge and auxiliary-power behavior.

How to interpret the result

Treat the primary result as an engineering screening value, then use the secondary outputs to understand scale, energy or operating impact. Confirm site measurements, equipment limits and applicable standards before making a design or control change.

Questions engineers ask

Is purge percentage based on dryer inlet flow or downstream plant demand?

This owner defines purge as a percentage of dryer inlet flow, so Qpurge = Qin × purge fraction. If a supplier states purge relative to delivered downstream air instead, first convert that basis; mixing the two definitions overstates or understates compressor load.

Why can desiccant-dryer purge vary so much by dryer type?

Heatless regenerative dryers often use a substantial share of dried compressed air for regeneration, while heated or blower-purge designs can use much less purge air and add heater/blower electricity. Enter the actual OEM or measured purge percentage for the installed cycle.

Does the power penalty include dryer heater or blower power?

No. The kW result values only the compressed air discarded as purge using the entered compressor specific power. Add dryer heater, blower, cooling and pressure-drop energy separately when those loads matter.

Continue the calculation

Use the next calculator in the same engineering workflow instead of restarting from search.

compressor specific powercompressed air system efficiencycompressed air moisture
Methodology. MAXScanner shows the governing formula, entered values and calculation outputs so the estimate is auditable. The calculator is a screening aid; assumptions and equipment-specific limits remain part of the engineering review.