Calculation sequence
Step-by-step method
- Subtract static head from known total head to isolate friction head.
- Scale friction head by the square of the flow ratio.
- Add unchanged static head to projected friction head.
MechanicalIntermediatePumps
Pump System Curve Calculator
Project total system head at a target flow using an entered static head and one known operating point.
Why it matters: Static head remains constant while friction head varies approximately with the square of flow.
Calculated result
Engineering evaluation
Projected total system head (H2)106.4 ft
- Projected friction head (Hf2)
- 86.4 ft
- Entered static head (Hs)
- 20 ft
- Flow ratio (rQ)
- 1.2 ratio
- Friction coefficient (K)
- 0 ft/(gpm)²
Engineering interpretation
The projected total system head at 600 gpm is 106.4 ft, including 20 ft static head and 86.4 ft projected friction head.
Important limitations
- This result extrapolates from one system point. Valve position, parallel paths, equipment staging, and flow regime can change the system curve.
Motor-driven equipment
Estimate electrical demand and energy use
Use nameplate information and an operating schedule to screen motor input power, current, annual energy, and operating cost. Results update automatically.
Choose the motor nameplate output-power convention.
Rated shaft output, not electrical input.
Used to estimate current; it does not change the hp-based energy result.
Use efficiency at the evaluated load point when available.
Use measured or defensible operating load rather than motor nameplate size alone.
Used only for the estimated current calculation.
Assumes all selected motors operate concurrently at the entered load.
Replace the profile with the actual occupied, process, or control schedule.
$/kWh
Use the applicable marginal utility energy charge; demand charges are not included.Estimated result
Total motor input power (Pin,total)6.21 kW
- Current per motor (I)
- 9.18 A
- Total coincident current (Itotal)
- 9.18 A
- Daily energy (Ed)
- 50 kWh/day
- Annual operating hours (Hy)
- 2,080 h/year
- Annual energy (Ey)
- 12,925 kWh/year
- Annual energy cost (Cy)
- $1,551/year
Equations and assumptions
Nameplate-based screening method
Horsepower is converted using 1 hp = 0.7457 kW. This estimate assumes steady average load and the entered operating-point efficiency. Voltage and power factor affect estimated current, but hp, load, efficiency, quantity, and schedule establish the energy estimate. VFD speed profiles, cycling, standby power, demand charges, and process variation require separate evaluation.
Technical basis: U.S. Department of Energy — Determining Electric Motor Load and EfficiencyEngineering knowledge center
Understand the calculation—not just the answer
Governing relationships
Hf1 = H1−Hs
K = Hf1/Q1²
rQ = Q2/Q1
Hf2 = Hf1rQ²
H2 = Hs+Hf2
Current substitution
Hf1 = 80−20 = 60 ft; H2 = 20+60×1.2² = 106.4 ft.
Equation legend
Inputs and calculated quantities
- Q1
- Known system flow — gpm or L/s
- H1
- Known total system head — ft or m
- Hs
- System static head — ft or m
- Q2
- Target system flow — gpm or L/s
- H2
- Projected total system head — ft
- Hf2
- Projected friction head — ft
- Hs
- Entered static head — ft
- rQ
- Flow ratio — ratio
- K
- Friction coefficient — ft/(gpm)²
Applications
How this calculation is used
Building design
Generate a preliminary system-curve point for pump selection.
Construction
Estimate the effect of a changed flow target in an unchanged piping system.
Commissioning
Compare measured head response with the ideal static-plus-quadratic relationship.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe the same stable operating condition.
- Units, pressure definitions, fluid properties, and equipment boundaries are applied consistently.
Limitations
- This tool supports preliminary evaluation and field verification; it does not replace manufacturer curves or project-specific engineering analysis.
- Project criteria, applicable standards, measurement uncertainty, and authorized professional judgment remain controlling.
Field use
Verification procedure
- Confirm the approved reference condition, instrument range, and calculation boundary.
- Stabilize the system and record calibrated field measurements.
- Compare the result with current manufacturer data and project requirements before disposition.
Common engineering mistakes
- Mixing measurements from different operating conditions or equipment boundaries.
- Treating a calculated screening status as automatic acceptance.
Technical basis
References and source standards
- U.S. Department of Energy—Improving Pumping System PerformanceFederal sourcebook covering pump head, power, efficiency, system curves, speed control, and pumping-system evaluation.
- ASHRAE Handbook—FundamentalsCurrent handbook chapters covering fluid flow, pressure relationships, system curves, and mechanical-system fundamentals; the licensed edition must be verified during professional review.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement