Calculator Input
Use the responsive form below. It shows three columns on large screens, two on smaller screens, and one on mobile devices.
Formula Used
Where:
- m = mass flow rate
- Cp = specific heat capacity
- ΔT = outlet temperature minus inlet temperature
- x = fraction of the stream undergoing phase change
- hfg = latent heat
- U = overall heat transfer coefficient
- A = heat transfer area
- LMTD = log mean temperature difference supplied by the user
How to Use This Calculator
- Select whether your known flow is mass based or volume based.
- Enter the flow rate and choose the correct unit.
- For volumetric flow, enter the fluid density.
- Enter specific heat, inlet temperature, outlet temperature, and units.
- Enable latent duty only when evaporation, condensation, or another phase change exists.
- Add efficiency and safety factor to estimate the practical design duty.
- Optionally enable the UA cross-check to compare demand against exchanger capacity.
- Press the calculate button to show results, chart, CSV export, and PDF export above the form.
Example Data Table
| Case | Flow Input | Cp | Temperature Change | Latent Input | Approx. Duty |
|---|---|---|---|---|---|
| Hot water coil | 2.5 kg/s | 4.186 kJ/kg·K | 25°C to 60°C | None | 366.28 kW |
| Steam condensing line | 1,200 kg/h | 0 | No sensible shift | 2,200 kJ/kg at 100% | 733.33 kW |
| Glycol cooling loop | 18 m³/h at 1,035 kg/m³ | 3.70 kJ/kg·K | 12°C to 7°C | None | 95.74 kW |
Frequently Asked Questions
1) What does heat duty mean?
Heat duty is the thermal load that must be added or removed from a stream, room, loop, or exchanger. It is commonly reported in kW, W, or Btu/h for design and equipment sizing.
2) Why does the calculator use mass flow?
Thermal energy depends on the actual mass being heated or cooled. When only volume flow is known, the calculator converts it to mass flow using the fluid density.
3) When should I include latent duty?
Use latent duty when condensation, evaporation, boiling, freezing, or another phase change occurs. If the fluid only changes temperature, keep latent duty disabled.
4) Why are safety factor and efficiency included?
Safety factor covers uncertainty, fouling, future load growth, and control margin. Efficiency adjusts the ideal duty into a more realistic design requirement for actual equipment performance.
5) What is the UA cross-check?
It compares required duty against exchanger capacity using U × A × LMTD. This helps verify whether the available surface and overall transfer coefficient can support the adjusted design load.
6) Can I use this for cooling and heating?
Yes. If outlet temperature is higher than inlet temperature, the tool reports heating duty. If outlet temperature is lower, it reports cooling duty while keeping load magnitudes positive for easy sizing.
7) What if my temperatures are entered in °F?
That is fine. The calculator converts the temperature difference to an equivalent Celsius or Kelvin difference internally, then performs the duty calculations consistently.
8) Are the energy results mandatory for design?
Not always. Instantaneous duty is usually enough for equipment sizing, but daily, monthly, and annual energy values are useful for utility planning, lifecycle estimates, and operating cost reviews.