Calculation sequence
Step-by-step method
- Confirm elapsed interval, accumulated runtime, and start-count reset behavior.
- Divide runtime by elapsed interval.
- Compare starts per hour with the user-entered screening limit.
MechanicalBeginnerControls
Runtime and Cycling Calculator
Calculate runtime percentage, cycles per hour, and average on-time from an observation interval.
Why it matters: Excessive cycling can indicate oversizing, poor control, low load, or equipment problems.
Calculated result
Engineering evaluation
Runtime fraction (RF)50 %
- Starts per hour (CPH)
- 0.5 1/h
- Average on-time per start (Ton)
- 60 min/start
Engineering interpretation
The interval shows 50% runtime, 0.5 starts per hour, and 60 minutes average on-time per start. Entered maximum is 6 starts per hour.
Important limitations
- Average metrics can conceal clustered cycling, lockouts, staging, mode changes, and trend gaps. Review the time series.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
RF = Tr/Te×100
CPH = N/Te
Ton = Tr·60/N
compare CPH with CPHmax
Current substitution
RF = 12/24×100 = 50%; CPH = 12/24 = 0.5; Ton = 60 min/start; CPHmax = 6.
Equation legend
Inputs and calculated quantities
- Te
- Observation interval — h
- Tr
- Accumulated runtime — h
- N
- Number of starts — count
- CPHmax
- Entered maximum starts per hour — 1/h
- RF
- Runtime fraction — %
- CPH
- Starts per hour — 1/h
- Ton
- Average on-time per start — min/start
Applications
How this calculation is used
Building design
Screen staging and part-load expectations.
Construction
Check status points and start counters.
Commissioning
Summarize equipment cycling from trend or counter data against a user-entered screening limit.
Quality controls
Assumptions and limitations
Assumptions
- Entered data describe one stable operating condition and use consistent measurement boundaries.
- Time, energy, and performance values are representative of the stated interval.
Limitations
- This is a preliminary evaluation and commissioning-support tool, not an automatic acceptance determination.
- Project sequences, manufacturer data, tariffs, codes, and professional review remain controlling.
Field use
Verification procedure
- Confirm the operating mode, test boundary, and instrument calibration.
- Collect simultaneous readings or a documented trend interval.
- Compare the result with the approved sequence, submittal, and project criteria.
Common engineering mistakes
- Combining measurements from different operating modes or time intervals.
- Ignoring sensor uncertainty, trend sampling, or the defined equipment boundary.
Technical basis
References and source standards
- ASHRAE Handbook—HVAC Systems and EquipmentHVAC equipment, central-plant, air-system, and control-performance context; verify the licensed current edition during professional review.
- U.S. Department of Energy—Better Buildings Solution CenterFederal HVAC energy-management and equipment-performance guidance.
- NIST Measurement and Calibration ResourcesFederal measurement, calibration, timing, and unit-system context.
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