Mechanical cooling while outdoor air temperature is in ideal free cooling range
Objective/Method/Outcome
Objective: Determines if mechanical cooling is operating when the outdoor air temperature is in ideal free cooling range
Method: Determines the Mechanical Cooling to be open by checking the Supply Fan Status is active and CCV is open. If the Mechanical Cooling is active when the outdoor air temperature is within free cooling range and the outdoor air damper is open below the threshold. The weekly hours of faulty operation are determined.
Outcome: Triggers an insight if mechanical cooling is operational when the outdoor temperature is in the ideal free cooling range.
Description
Monitors CCV and OAT to determine if mechanical cooling is active while outdoor air temperature is in ideal free cooling range.
This rule is part of the CopperTree Standard ruleset and is derived from NIST APAR15.
Default Priority
Medium
Diagnosis
- Input sensor(s) faulty or miscalibration. Verify input sensor(s) operation.
- Check AHU control logic, ensure mechanical cooling with min OA is not being used when mechanical cooling with 100% OA should be used (when OAT is lower than changeover set point).
Message
Mechanical cooling is active while outdoor air temperature is in ideal free cooling range.
Rule Template
Insight Type: Fault Detection
Trigger Type: Active High
Logic
Inputs
| Input | Unit | Tags | Description |
|---|---|---|---|
| Outdoor Air Temperature | °C/ °F | Outdoor Air Temperature | The recorded outdoor air temperature |
| Outdoor Air Damper | Outdoor Air Damper Position, Outdoor Air Damper Command | The recorded position of outdoor air damper | |
| Outdoor Air Temperature Low Limit | °C/ °F | The lower limit of the outdoor air temperature range | |
| Outdoor Air Temperature High Limit | °C/ °F | The upper limit of the outdoor air temperature range | |
| Outdoor Air Damper Threshold | % | The minimum position of the damper to determine if OAD is open | |
| Threshold – Weekly Hours of Faulty Operation | Hr | The minimum hours of faulty operation to trigger insight | |
| CCV | Discharge Air Cooling Command | The status of the cooling system | |
| SF Status | Discharge Air Fan Command, Discharge Air Fan Status | The status of the supply fan |
Notes
This rule compensates for the temperature rise across a supply fan between the MAT and SAT sensors. This value varies per system, and the parameter should be changed within the logic flow accordingly. The temperature rise over a fan is currently set to 1.1 degrees in accordance with NIST recommendations.
Default Thresholds:
- OAT Low Limit: 5°C or 41 °F
- OAT High Limit: 17°C or 63 °F
- OAD Position: <35%
- Weekly Hours of Faulty Operation: 8