Objective/ Method/Outcome
Objective: Determines if the return airflow is within the supply airflow threshold.
Method: Compares the return airflow to the supply airflow and the defined high and low limit thresholds. If the return airflow is outside of the thresholds, the hours of faulty operation are calculated. Avoidable Cost and Potential Savings are calculated based on the Energy Rate.
Outcome: This rule generates an insight if the Weekly Hours of Faulty Operation exceeds the acceptable weekly threshold.
Description
Reference:ASHRAE36-5.16.11/ASHRAE90.1-6.5.3.2.4
Return airflow shall be controlled to maintain building pressure either directly, or indirectly through differential supply-return airflow tracking. 10%-20% less return airflow than supply airflow is considered normal in most cases.
This rule is part of the CopperTree Standard rule-set. (Aliased Celsius / Aliased Fahrenheit)
Default Priority
Medium
Diagnosis
1. Inspect the equipment to see if it has been overridden manually.
2. Review control sequence.
Message
Return fan speed is not controlling properly
Rule Template
Insight Type: Fault Detection
Trigger Type: Active High
Notes
1. Expected values for SF/RF rated CFM are “0” If an airflow station is present.
2. Expected values for SF/RF rated CFM are from building documents if airflow station is not present.
3. Only one “Airflow”, [LPS] or [CFM] is needed.
4. The input(s) that is(are) not used should be set to “0”.
Default Values:
Const. – Return Fan High Limit Threshold of Supply Fan Airflow/Speed [%]: 90
Const. – Return Fan Low Limit Threshold of Supply Fan Airflow/Speed [%]: 80
Const. – Threshold – Acceptable Weekly Hours of Faulty Operation [hrs]: 4
Const. – Return Fan Rating [hp]: 10
Const. – Energy Rate [$/kWh]: 0.1
Const. – Weeks of Operation [weeks]: 52
CTLs:
RF Airflow mismatch with SF Airflow – Weekly Hours of Faulty Operation (KPI)
RF Airflow mismatch with SF Airflow – Hours of Faulty Operation (CUSUM)
RF Airflow mismatch with SF Airflow- Avoidable Cost [$]
RF Airflow mismatch with SF Airflow- Potential Savings [$/year]
