Use consistent units. Temperature rise uses the same scale as °C.
These example rows show typical inputs and the resulting design duty. Values are illustrative.
| m (kg/s) | T_in (°C) | T_out (°C) | Cp (kJ/kg·K) | η (%) | Loss (kW) | Margin (%) | Design duty (kW) |
|---|---|---|---|---|---|---|---|
| 25.00 | 90 | 150 | 4.19 | 92 | 15 | 10 | 7,531.2 |
| 18.00 | 70 | 120 | 4.18 | 90 | 10 | 8 | 4,525.2 |
| 40.00 | 105 | 165 | 4.20 | 93 | 25 | 12 | 12,167.4 |
| 12.00 | 60 | 110 | 4.18 | 88 | 8 | 5 | 3,000.9 |
| 30.00 | 95 | 145 | 4.19 | 91 | 18 | 10 | 7,617.1 |
- Temperature rise: ΔT = Tout − Tin
- Feedwater sensible duty: Qfw = ṁfw · Cp · ΔT
- Efficiency and losses: Qreq = (Qfw / (η/100)) + Qloss
- Design margin: Qdesign = Qreq · (1 + Margin/100)
- Steam-side available duty (optional): Qsteam = ṁsteam · (hin − hout)
Unit check: kg/s × kJ/kg·K × K = kJ/s = kW. The steam-side check helps confirm extraction steam capacity.
- Enter feedwater mass flow, inlet temperature, and outlet temperature.
- Set Cp to match your expected temperature range.
- Apply heater efficiency and any heat loss allowance.
- Add a design margin for fouling and operating variability.
- Enable steam-side check only if you have enthalpy data.
- Press Calculate to view results above the form.
- Download CSV or PDF outputs for project documentation.
Duty estimation for construction-stage planning
Feedwater heater duty drives utility sizing during plant construction and early commissioning. A reliable duty estimate helps set steam extraction piping sizes, condensate drain routing, and insulation thickness. It also supports preliminary electrical loads for pumps and control systems tied to temperature regulation. By entering flow, inlet temperature, outlet temperature, and efficiency, you can produce a design duty that aligns with procurement schedules and field installation constraints.
Energy balance and unit consistency
The calculator applies a simple energy balance: sensible heat required equals mass flow times specific heat times temperature rise. Because the inputs use kilograms per second and kilojoules per kilogram–kelvin, the result naturally appears in kilowatts. Conversions to megawatts, megajoules per hour, and Btu per hour support mixed project documentation and vendor datasheets.
Efficiency, losses, and design margin
Real heaters do not transfer heat perfectly. Tube fouling, venting, and imperfect approach temperature reduce effective performance. The efficiency field lets you translate useful feedwater duty into required heater input duty. A separate loss allowance captures casing and nearby piping losses, while a design margin provides contingency for variability, degradation, and operating flexibility.
Steam-side verification for extraction systems
When steam data is available, the optional steam-side check estimates available duty from steam flow and enthalpy drop across the heater. Comparing that available duty with the feedwater requirement highlights surplus or shortfall conditions. This is helpful when coordinating turbine extraction limits, pressure control valves, and drain cooler arrangements during integrated mechanical completion. It also helps validate instrument ranges for flow, temperature, and level control.
Documentation and handover readiness
Construction teams benefit from repeatable calculations that can be shared across disciplines. Exporting CSV supports quantity takeoffs and cost models, while the PDF summary fits into commissioning dossiers and quality records. Keep a consistent basis of design: record assumptions for Cp, efficiency, losses, and margin, then re-run after hydrotest and performance verification. Document the final duty used for setting valve Cv and relief provisions during startup load steps.
FAQs
1) What is feedwater heater duty in this tool?
It is the heat rate required to raise feedwater from the inlet temperature to the outlet temperature, adjusted for heater efficiency, losses, and any design margin. Results are shown in kW with common unit conversions.
2) Which inputs affect duty the most?
Mass flow and temperature rise have the biggest impact because duty is proportional to both. Specific heat has a smaller influence, while efficiency, losses, and margin increase the required heater input duty.
3) When should I use the steam-side check option?
Use it when you know steam flow and enthalpy values from steam tables or plant data. It estimates available steam duty and compares it with the feedwater requirement to indicate surplus or shortfall.
4) Does ambient temperature change the calculation?
No. Ambient temperature is stored for reporting and documentation only. If you want to model heat losses more precisely, adjust the heat loss allowance based on insulation design and site conditions.
5) How do I choose an efficiency value?
Use vendor guarantees when available. For early estimates, use a conservative efficiency to reflect approach temperature, venting, and fouling. Revisit the value after commissioning tests or performance verification.
6) What should I export for project records?
Export CSV for spreadsheets, cost models, and comparison runs. Export PDF for commissioning packs, design reviews, and handover documentation. Always keep a note of assumptions for Cp, losses, and margin.