Inputs
Choose whether you already know TDH, or calculate it from components. Enter total system flow; duty pumps share flow equally in parallel.
Example data table
These examples illustrate typical ranges for building booster systems. Use project specifications and local codes for final selection.
| Scenario | Flow (m³/h) | TDH (m) | Duty / Standby | Recommended motor (kW) |
|---|---|---|---|---|
| Low-rise apartments (peak demand) | 20 | 35 | 1 / 1 | 5.5 |
| Mid-rise commercial (pressure critical) | 35 | 55 | 2 / 1 | 11 |
| Industrial utilities (higher friction losses) | 60 | 65 | 2 / 2 | 22 |
Formula used
1) Total Dynamic Head (TDH)
- TDH = (Static Lift + Friction Head + Minor Losses + Pressure-Rise Head) × (1 + Safety)
- Pressure-rise head converts pressure difference to head: Hp = ΔP / (ρ g)
2) Hydraulic and motor power (per duty pump)
- Flow per duty pump: Qpump = Qtotal / Nduty
- Hydraulic power: Phyd = ρ g Qpump TDH
- Shaft power: Pshaft = Phyd / ηpump
- Motor input: Pmotor = Pshaft / ηmotor
3) NPSH available (informative estimate)
- NPSHa ≈ Hatm − Hvapor − Suction Lift − Suction Losses
- Always compare with the selected pump’s NPSH required at duty flow.
How to use this calculator
- Enter the total system flow and choose the correct unit.
- Select Calculate TDH to build TDH from components, or enter TDH directly.
- Set pump and motor efficiencies based on vendor data or typical ranges.
- Choose the number of duty pumps; the tool sizes each duty pump equally.
- Fill altitude, temperature, and suction values to estimate NPSH available.
- Press Calculate and review results shown above the form.
- Use the download buttons to export CSV or PDF for documentation.
Project guidance
Demand and duty point definition
Start by confirming the design flow at peak simultaneous demand, not average use. Align the duty point with the most demanding operating condition, such as top-floor fixtures plus fire or process allowances where applicable. Oversizing increases cycling and energy use, while undersizing causes pressure instability and user complaints.
Head components that drive sizing
Total Dynamic Head is built from elevation rise, pressure requirement at the most remote outlet, and hydraulic losses through piping and fittings. Friction losses grow rapidly with flow, so validate pipe diameters and valve selections before finalizing head. Apply a modest safety factor to cover aging, fouling, and minor scope changes.
Efficiency and motor margin
Use realistic pump efficiency near the selected duty point and avoid relying on best-case catalog values. Motor efficiency affects input power and heat, especially for continuous operation. The recommended motor rating should include margin for voltage variation, temperature rise, and short-term overload during transient events.
Parallel duty pumps and redundancy
For parallel duty pumps, the total flow is divided across operating pumps while head remains approximately the same. Multiple duty pumps can improve part-load efficiency when staged correctly. Add standby capacity to maintain service during maintenance or failure, and confirm controls can prevent unstable operation at low demand.
Suction conditions and cavitation risk
Use the NPSH available estimate to screen suction risk. Higher altitude reduces atmospheric pressure and warm water raises vapor pressure, both lowering NPSH available. Keep suction piping short, avoid sharp fittings, and maintain adequate submergence to reduce losses and air entrainment at the pump inlet.
Example data
Example input set for a two-pump duty arrangement: Total flow 36 m³/h, static lift 22 m, friction head 18 m, minor losses 5 m, discharge pressure 380 kPa, suction pressure 70 kPa, safety 10%, pump efficiency 68%, motor efficiency 90%. Review the calculated TDH and per-pump power to confirm a practical motor size.
FAQs
1) What is booster pump sizing used for?
It estimates the head and flow a pump must deliver so building fixtures and equipment meet minimum pressure. It also converts that duty point into power and a practical motor rating.
2) How do I choose the design flow?
Use peak simultaneous demand from fixture units, occupancy, or process needs. Confirm if the duty point must cover special cases like rooftop tanks, irrigation, or washdown at the same time.
3) Why include a safety factor on TDH?
It accounts for modeling uncertainty, future fittings, pipe roughness changes, and minor field variations. Keep it modest; oversized safety factors can push the selection into inefficient operating zones.
4) What happens when I add more duty pumps?
Each duty pump handles a smaller share of total flow, while head stays about the same. Staged operation can reduce energy use at part load if controls manage sequencing smoothly.
5) Is the NPSH value in this tool enough for final selection?
No. Use it as a screening estimate. Final selection must compare NPSH available to the manufacturer’s NPSH required curve at the chosen duty point and expected operating temperature.
6) Which efficiency values should I use?
Use vendor curves at the target duty point for the selected impeller and speed. If unknown, use conservative typical values, then refine once you shortlist pump models.
7) How should I document results for approvals?
Export CSV or PDF from the latest run, then attach pump curves, control sequence notes, and assumptions for losses and pressures. This keeps calculations traceable during reviews and commissioning.