Objective/ Method/Outcome
Objective: Determines if total VAV airflow is less than the associated AHU airflow.
Method: Compares the total VAV airflow from up to 24 VAVs to the airflow of the associated AHU. If total VAV airflow is less than the AHU airflow by the allowable percentage of airflow leakage, the hours of faulty operation are calculated. Avoidable Cost and Potential Savings are calculated based on the Natural Gas Rate and Electricity Rate.
Outcome: This rule generates an insight if the Weekly Hours of Faulty Operation exceeds the acceptable weekly threshold.
Description
This is managed service specific rule. It calculates the total airflow from all VAVs associated with same AHU and compare with AHU airflow. An insight will be triggered if calculated airflow from all VAVs is much less than AHU airflow.
This rule is part of the CopperTree Standard rule-set. (Aliased Celsius)
Default Priority
Medium
Diagnosis
1. Check AHU fan status and VAV air flow sensors
2. Check any AHU opening / duct work leaks
Message
VAV total airflow is less than airflow delivered from upstream AHU.
Rule Template
Insight Type: Fault Detection
Trigger Type: Active High
Notes
1. Add ‘VAV Airflow’ Input blocks if necessary.
2. Expected value for AHU rated CFM is “0” If an airflow station is present.
3. Expected value for AHU rated CFM is from building documents if airflow station is not present.
4. Expected values for “AHU Supply Fan” inputs are “0” or “1”.
5. Only one “Airflow”, [LPS] or [CFM] is needed.
6. The input(s) that is(are) not used should be set to “0”.
Default Values:
Const. – Allowable % Airflow Leakage: 15
Const. – AHU Fan Power Rating [hp]: 10
Const. – Electricity Rate($/kWh): 0.1
Const. – Natural Gas Rate ($/mmBTU): 3
Const. – Weeks of Operation: 52
Const. – Threshold for Faulty Hours Per Week: 8
CTLs:
VAV Airflow Sum [CFM]
AHU Airflow [CFM]
AHU Airflow Leak [CFM]
AHU Airflow Percentage Leak [%]
AHU Airflow Leaking – Weekly Hours of Faulty Operation (KPI)
AHU Airflow Leaking – Hours of Faulty Operation (CUSUM)
AHU Airflow Leaking – Avoidable Cost [$]
AHU Airflow Leaking – Potential Savings [$/Year]
