Evaporator Capacity Calculator

Size evaporator loads with clear unit conversions. Adjust for fouling, safety, partload, and derates easily. Get capacity in kW, BTUhr, and tons fast now.

Evaporator Capacity Inputs
Choose a method, enter measurements, and apply margins.
Pick based on available field data.
The calculator converts automatically.
Reduces gross capacity for fouling and losses.
Use 100 for full load, lower for typical operation.
Adds margin for design sizing.
Air-side inputs
Total capacity from enthalpy
Typical coil data uses airflow and conditions.
1.20 is a common standard assumption.
Use site altitude correction if needed.
Water-side inputs
Flow and temperature rise/drop
Used for a simple Cp adjustment.
Refrigerant-side inputs
Mass flow and enthalpy lift
Reset
Formula used
  • Air-side: Q = ṁda · (hin − hout), where h is moist-air enthalpy (kJ/kg dry air).
  • Water-side: Q = ṁ · Cp · ΔT using mass flow from density and volumetric flow.
  • Refrigerant-side: Q = ṁ · Δh based on enthalpy rise across the evaporator.
  • Adjustments: Qadj = Q · (1−derate) · part-load, then Qdesign = Qadj · (1+safety).
This tool uses practical engineering approximations for quick sizing and comparison.
How to use this calculator
  1. Select the method that matches your available site measurements.
  2. Choose SI or Imperial units, then enter the required inputs.
  3. Set derate, part-load, and safety factor to reflect project conditions.
  4. Press Calculate capacity to view results above the form.
  5. Use CSV or PDF export for design notes and reporting.
For commissioning, use measured flows and temperatures, not nameplate values.
Example data table
Illustrative values
Scenario Method Key inputs Gross capacity
Office AHU coil check Air-side 2500 m³/h, 27°C 50% → 12°C 90% ~21 kW (varies with density)
Chilled water loop Water-side 120 L/min, 12°C → 7°C, Cp 4.186 ~41.9 kW
Refrigerant test point Refrigerant 0.08 kg/s, 250 → 420 kJ/kg ~13.6 kW
Use the example rows as a sanity check for unit handling and magnitudes.

Load meaning and reporting units

Evaporator capacity is the heat absorption rate from air or water. Site documents commonly use kW, tons of refrigeration (TR), or kBtu/h. Keep units consistent when checking submittals: 1 TR = 3.517 kW = 12,000 Btu/h. Record whether capacity is gross (coil only) or net after fan and cabinet heat.

Air-side method for AHUs and FCUs

Air-side capacity depends on airflow and enthalpy drop across the coil. Enthalpy captures both sensible and latent cooling, so it is preferred when humidity changes. Field checks typically measure dry-bulb, relative humidity, and airflow at stable damper and filter conditions, then compare against design leaving air targets.

Water-side method for chilled water coils

Hydronic capacity is Q = ṁ·Cp·ΔT, with water Cp ≈ 4.186 kJ/kg·K. A quick rule: 1.0 L/s at ΔT 5°C is about 20.9 kW. Verify flow meter calibration, purge air from the loop, and insulate temperature probes to reduce ambient error.

Refrigerant-side method for DX systems

For direct expansion equipment, Q = ṁ·(hin−hout). Use manufacturer P-h data to estimate enthalpies from pressures and line temperatures. Confirm superheat and subcooling are within expected ranges; abnormal values can indicate charge issues that distort capacity interpretation.

Design adjustments and commissioning notes

Construction conditions vary with occupancy, infiltration, and fouling. The adjustment block allows altitude correction (air density), fouling loss, and a safety margin. Document assumptions in the test report. Persistent shortfall above 10% typically warrants balancing, coil cleaning, or control sequence review. Track approach temperature between air and fluid; widening approach often signals fouling. Re-test after corrections and archive before/after readings.

Example input set
MethodInputsExpected result
Water-sideFlow 1.2 L/s, ΔT 6°C≈ 30.1 kW
Air-sideAirflow 2200 m³/h, h: 55 → 32 kJ/kg≈ 19–22 kW
Refrigerant-sideṁ 0.06 kg/s, Δh 140 kJ/kg≈ 8.4 kW

FAQs

1) Which method should I use on a construction site?

Use the method that matches your measured variables. Air-side is best for AHU/FCU checks, water-side for chilled water coils, and refrigerant-side for DX troubleshooting when pressures and temperatures are reliable.

2) Why does air-side capacity differ from water-side results?

Differences come from sensor placement, airflow measurement error, stratification, and unaccounted loads like fan heat or cabinet losses. Compare at steady operating conditions and verify instruments before assuming the coil is undersized.

3) What is a normal chilled-water coil ΔT?

Many designs target 4–6°C (about 7–10°F), but it depends on flow strategy and coil selection. Low ΔT may indicate excess flow, bypassing, or control issues; high ΔT may indicate low flow or fouling.

4) How accurate is the altitude adjustment?

Altitude correction improves air-side estimates by scaling air density. It is suitable for sizing and comparison, but final selections should still reference manufacturer performance data for the project elevation and expected entering conditions.

5) Should I include safety margin in commissioning reports?

Yes. Note any applied margin and why it was used. Margins help cover measurement uncertainty and short-term construction variability, but they should not hide persistent capacity deficits that require corrective action.

6) What does “fouling factor” represent here?

It represents expected reduction in heat transfer due to dust, scale, or coil film. Enter 0% for clean conditions, then increase if filters are loaded, fins are dirty, or water quality is poor and scaling is possible.

7) Can I use this for heating coils?

Yes, with the same equations, because it is still heat transfer rate. Use appropriate entering and leaving temperatures, and interpret the sign as heating. For steam coils, ensure you use condensate conditions consistent with the coil design.

Related Calculators

Paver Sand Bedding Calculator (depth-based)Paver Edge Restraint Length & Cost CalculatorPaver Sealer Quantity & Cost CalculatorExcavation Hauling Loads Calculator (truck loads)Soil Disposal Fee CalculatorSite Leveling Cost CalculatorCompaction Passes Time & Cost CalculatorPlate Compactor Rental Cost CalculatorGravel Volume Calculator (yards/tons)Gravel Weight Calculator (by material type)

Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.

?>