TOOL GUIDE
Head loss & pump sizing
Calculate pump head and power for closed/open water systems from path losses and outlet requirements.
Purpose & scope
Calculate pump head and power for closed/open water systems from path losses and outlet requirements.
Closed-loop circulation excludes building elevation. Open systems assume an atmospheric source; pressurized source effects and NPSH are not calculated.
Inputs
Use drawings, design conditions and manufacturer data. Units and example values follow the calculator; example values are not universal design requirements.
| Parameter | Value / interpretation |
|---|---|
| Proposed pump type | Not specified / End-suction centrifugal / Inline centrifugal / Double-suction centrifugal / Multistage |
| Application | Chilled-water circulation / Condenser water / Water supply / pressure boosting |
| System type | Chiller / closed loop / Water supply / open system |
| Pump flow · m³/h | Volumetric flow at the calculation location; check the selected unit. |
| Water temperature · °C | Water temperature used for fluid properties. |
| Pipe roughness · mm | Absolute roughness of the internal pipe/duct surface, in mm. |
| Elevation from source to outlet · m | Source-to-outlet elevation for open systems; excluded from closed-loop circulation head. |
| Required outlet residual pressure · kPa | Required residual pressure at the outlet of an open system, in kPa. |
| Additional head · mH₂O | Additional losses not included in path rows; avoid double counting. |
| Head allowance · % | Allowance applied to the result; not a substitute for entering all losses. |
| Pump efficiency · % | Fan/pump efficiency at duty, from manufacturer data. |
| Motor efficiency · % | Motor efficiency used to estimate electrical input power. |
Steps
- Select closed/open system and enter flow, temperature, roughness and efficiencies.
- For closed loops include supply and return; use internal diameter and equipment Δp in kPa.
- For open systems enter elevation and residual pressure. Verify Q–H, NPSH, operating range and motor against catalogue data.
Worked example
This reproducible training example uses the values below. Select the appropriate mode and overwrite restored project values. Example rates, K values and equipment losses are assumptions, not mandatory design criteria.
Examples use a decimal point and no thousands separator.
All example inputs
| Parameter | Value / interpretation |
|---|---|
| Proposed pump type | Not specified |
| Application | Chilled-water circulation |
| System type | Chiller / closed loop |
| Pump flow | 10 m³/h |
| Water temperature | 7 °C |
| Pipe roughness | 0.045 mm |
| Elevation from source to outlet | 15 m |
| Required outlet residual pressure | 100 kPa |
| Additional head | 0 mH₂O |
| Head allowance | 10 % |
| Pump efficiency | 65 % |
| Motor efficiency | 90 % |
Replace the default path with exactly this row; delete the other sample rows.
| Parameter | Value / interpretation |
|---|---|
| Section | Example calculation path |
| Section flow | 10 m³/h |
| Section dimensions | D 65 mm |
| Section length | 60 m |
| Total fitting K | 2 |
| Equipment pressure loss | 30 kPa |
Expected results (rounded)
| Parameter | Value / interpretation |
|---|---|
| Pump head | 4.32 mH₂O |
| Shaft power | 0.181 kW |
Small differences in displayed rounding are normal. A result that passes the entered limits does not establish suitability for the complete system.
Method & limitations
Closed-loop circulation excludes building elevation. Open systems assume an atmospheric source; pressurized source effects and NPSH are not calculated.
Enter consecutive sections of the critical path, including supply and return in closed loops. Do not sum parallel branches.
H = Σ(f·L/D + K)·v²/(2g) + equipment head. Closed loops exclude building height from circulation head; fill pressure must be checked separately. Open systems add elevation and residual pressure, assuming an atmospheric source and negligible endpoint velocity-head difference.
Pure water only; not a glycol model. The motor size is a shaft-power guide; verify the pump curve, NPSH, duty point and operating range.
Common mistakes
Adding building height to a closed loop; confusing DN/internal D or kPa/mH₂O; ignoring source pressure and NPSH.
Projects & reports
- Choose or create an engineering project and enter your actual design inputs.
- Project inputs/results are autosaved in this browser. Where a saved-list panel is available, name and add the selected section or alternative to compare multiple options.
- Review the report before exporting PDF. In the print dialog select Save as PDF. Export JSON for backup and use Open file to restore it; PDF cannot restore project data.
Saved results do not automatically recalculate when another tool changes. Review any dependency warning, recalculate and update the affected results.
References & related tools
Caleffi — Hydronic operating conditions
The tool implements the methods and limits stated above; linking a standard does not establish complete compliance with that standard.