Objective/Method/Outccome
Objective: Determines if VFD is constantly running at high speed for more than the acceptable amount of time during hours of operation.
Method: Compares the VFD speed and VFD speed threshold during hours of operation and determines if the speed exceeded the threshold for more than the acceptable time. Calculates the potential savings by a 10% reduction in speed.
Outcome: An Energy Insight is created and Potential Savings calculated.
Applicable Systems
CWS, HWS, DAF, RAF
Description
Monitors VFD speeds to determine if they are consistently running at a high speed. Potential savings are calculated assuming a 10% reduction in speed, however this value can be modified on a per-VFD basis.
This rule is part of the CopperTree Standard rule-set.
Diagnosis
- VFD may be manually overridden.
- Static pressure sensor may be faulty.
- Review SSP control.
- Fan capacity is not sufficient.
Message
VFD runs consistently at high speed. A 10% reduction in speed can result in nearly 30% less electricity consumption.
Rule Template
Insight Type: Energy
Trigger Type: Active High
Default Priority
Medium
Logic
Inputs
| Input | Unit | Tags | Description |
|---|---|---|---|
| VFD Speed | Chilled Water Pump VFD Speed, Hot Water Pump VFD Speed, Discharge Air Fan VFD Speed, Return Air Fan VFD Speed | The recorded speed | |
| Energy Rate | $/kWh | ||
| Yearly Weeks of Operation | The number of weeks the fan is operational | ||
| VFD Rating | HP | The energy rating of the fan | |
| Threshold – Potential Savings Yearly | The minimum amount of savings the reduction should make to create an insight | ||
| Speed Threshold | % | The minimum speed that may create the insight | |
| Speed Reduction | % | The assumed speed reduction. This is used to calculate Potential Savings |
Notes
Default Values:
- Potential Savings Threshold: $100
- Speed Threshold: 95%
- Speed Reduction: 10%
- VFD Rating [HP]: 10
The calculation is done using VFD affinity law, where speed and power consumption have a cubic relationship. A 10% reduction in speed results in 27.1% less energy usage.
More information on Affinity Law: https://www.engineeringtoolbox.com/affinity-laws-d_408.html
