Calculation sequence
Step-by-step method
- Calculate working drawdown from basin area and level difference.
- Calculate pump-on time from net drawdown flow and refill time from inflow.
- Divide 60 minutes by total cycle time.
PlumbingAdvancedSump and Drainage Pumps
Sump-Basin Cycling Calculator
Estimate working drawdown volume, pump-on time, refill time, and starts per hour for a constant-area basin.
Why it matters: Basin geometry, inflow, pump flow, and level spacing determine cycling; manufacturer limits remain external inputs and review criteria.
Calculated result
Engineering evaluation
Calculated starts per hour (Nˢ)12.833 starts/h
- Working drawdown volume (Vᵈ)
- 74.805 gal
- Pump-on time (tᵒⁿ)
- 0.935 min
- Pump-off refill time (tᵒᶠᶠ)
- 3.74 min
Engineering interpretation
The constant-condition model yields 12.83333 starts/h, 0.9350649 min on, and 3.74026 min off.
Important limitations
- No hidden cycling acceptance limit is applied. Confirm manufacturer allowable starts, motor cooling, basin geometry, retained volume, level spacing, variable inflow, pump/system curve, controls, duplex alternation, lag start, high-level storage, alarms, and sewage/sump hazards.
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
Vᵈ=Aᵇ(ΔH/12)·7.48051948 (I-P) or Aᵇ(ΔH/1000)·1000 (SI)
tᵒⁿ=Vᵈ/(Qᵖ−Qᵢ)
tᵒᶠᶠ=Vᵈ/Qᵢ
Nˢ=60/(tᵒⁿ+tᵒᶠᶠ)
Current substitution
Vᵈ=74.80519; tᵒⁿ=74.80519/(100−20)=0.9350649 min; tᵒᶠᶠ=74.80519/20=3.74026 min; Nˢ=12.83333 starts/h.
Equation legend
Inputs and calculated quantities
- Aᵇ
- Basin plan area — ft² or m²
- ΔH
- Start-to-stop level difference — in or mm
- Qᵢ
- Steady inflow — gpm or L/min
- Qᵖ
- Pump discharge flow — gpm or L/min
- Nˢ
- Calculated starts per hour — starts/h
- Vᵈ
- Working drawdown volume — gal
- tᵒⁿ
- Pump-on time — min
- tᵒᶠᶠ
- Pump-off refill time — min
Applications
How this calculation is used
Building design
Screen basin drawdown and cycling relationships.
Construction
Check level spacing and basin geometry.
Commissioning
Compare observed cycling with a transparent steady-inflow model.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe one documented system and use a consistent unit, energy, pressure, elevation, and measurement basis.
- Measurements are representative and synchronized where the calculation combines field readings.
Limitations
- Constant basin area, inflow, and pump flow are assumed; retained/check-valve volume, control delay, variable inflow, and system-curve interaction are omitted.
- No hidden starts-per-hour limit is applied. Manufacturer limits, cooling, level spacing, high-level storage, alternation, lag start, alarms, and code criteria require review.
Field use
Verification procedure
- Confirm the calculation boundary, source documents, formula symbols, and units.
- Record representative field values or approved project inputs and their sources.
- Review the result against the applicable code, criteria, manufacturer data, and measurement uncertainty.
Common engineering mistakes
- Combining values from different system boundaries, operating periods, temperature bases, or unit conventions.
- Treating a calculated screening value as a hidden pass/fail threshold or final design decision.
Technical basis
References and source standards
- International Plumbing Code, 2024The legally adopted edition and local amendments govern water, sanitary, storm, sump, and pumping requirements; protected code tables are not reproduced.
- Hydraulic InstitutePump-system, test-boundary, and manufacturer-curve context; exact equipment data remain controlling.
- NIST SI and Unit Conversion GuidanceUnit symbols, pressure, flow, energy, temperature, and dimensional conversions used by the application.
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