Calculator Inputs
Use direct flow when you already know the building peak demand. Use fixture units when you want a quick estimating method.
Example Data Table
| Example Item | Value | Unit | Comment |
|---|---|---|---|
| Project | 15-Storey Apartment Block | - | Illustrative domestic water booster example. |
| Direct Design Flow | 720 | L/min | Known peak demand from design brief. |
| Duty / Standby | 2 / 1 | pumps | Two operating pumps and one spare. |
| Static Discharge Head | 38 | m | Vertical rise to the highest outlet. |
| Suction Head / Lift | 2 | m | Positive value means suction lift. |
| Outlet Pressure | 2.2 | bar | Residual pressure at the top fixture. |
| Equivalent Length | 120 | m | Pipe plus fittings converted to length. |
| Friction Loss | 7 | m/100m | Approximate design loss rate. |
| Minor Loss | 4 | m | Valves, elbows, and fittings allowance. |
| Estimated Design Result | ≈ 82.3 head, 360 per duty pump | m, L/min | Rounded result with safety margin. |
Formulas Used
- Direct flow mode: Base Flow = Entered Design Flow.
- Fixture-unit mode: Base Flow = Coefficient × √(Fixture Units) × Simultaneity Factor.
- Design Flow: Design Flow = Base Flow × (1 + Future Expansion %).
- Residual Pressure Head: Pressure Head = Pressure in bar × 10.197.
- Friction Head: Friction Head = Friction Loss per 100m × Equivalent Length / 100.
- Total Dynamic Head: TDH = Static Head + Residual Pressure Head + Friction Head + Minor Loss Head.
- Recommended Design Head: Recommended Head = TDH × (1 + Safety Margin %).
- Hydraulic Power: P = 9.81 × Specific Gravity × Flow(m³/s) × Head(m).
- Brake Power: Brake Power = Hydraulic Power / Pump Efficiency.
- Motor Input: Motor Input = Brake Power / Motor Efficiency.
This calculator uses a practical estimating workflow. Final pump selection should always be checked against the manufacturer performance curve, available NPSH, control philosophy, and project specifications.
How to Use This Calculator
- Enter the project name for your report.
- Select direct flow if peak demand is known, or fixture units for an estimate.
- Provide duty and standby pump counts.
- Enter static head, required pressure, and piping losses.
- Add efficiencies, safety margin, and operating assumptions.
- Press the calculate button to see the result above the form.
- Review the recommended head, flow per pump, power, and operating cost.
- Use the CSV or PDF button to download a quick report.
FAQs
1) What does this booster pump size calculator estimate?
It estimates design flow, total dynamic head, motor input, energy use, and a practical booster pump arrangement for building water systems. It helps create a quick sizing starting point before final manufacturer selection.
2) Should I use direct flow or fixture units?
Use direct flow when the hydraulic design already defines peak demand. Use fixture units when you need a fast estimate during concept design. The direct method is usually better for final equipment selection.
3) Why is required outlet pressure included?
Booster pumps must deliver enough pressure at the highest or worst-case outlet. That pressure becomes additional head, and ignoring it often causes undersized pumps and poor service performance at upper floors.
4) Why do I need equivalent pipe length?
Equivalent length converts fittings and valves into a pipe-loss allowance. It helps estimate friction head without a full hydraulic model. Longer effective piping means more head loss and larger pump demand.
5) How many duty pumps are usually selected?
Many building systems use two duty pumps sharing the peak load, plus one standby pump for reliability. Smaller systems may use one duty and one standby. The best arrangement depends on redundancy goals and turndown control.
6) Is the recommended motor size the exact purchase size?
It is a rounded practical recommendation using the next standard motor size above the calculated demand. Final purchase size should still consider service factor, starting method, ambient conditions, and manufacturer data.
7) Can this calculator replace a manufacturer pump curve check?
No. It gives a strong preliminary sizing result, but final selection must confirm efficiency, NPSH, control range, impeller diameter, and operating point on an actual manufacturer curve.
8) Should I include a standby pump?
A standby pump improves reliability, simplifies maintenance planning, and reduces service interruptions. For residential, hotel, hospital, and school projects, standby capacity is commonly preferred where uninterrupted water service matters.