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EDC Building | Fault Detection & Diagnostics | Supply Air Pressure Reset

Fully Open Dampers
Health Index = %
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Supply Air Pressure (SAP) Reset

The Fully Open Dampers chart lets you monitor the proportion of time that a certain number of VAV unit dampers are simutaneously fully open based on the number of fully open dampers - it can be used to assess the presence and functionality of a supply air pressure (SAP) reset policy. A SAP reset policy ensures a steady and appropriate amount of pressure in the supply air. Inadequate supply air pressure may result in insufficient airflow delivery, resulting in poor indoor air conditions. Alternatively, excess supply air pressure may result in excess fan energy use.

Ideally, the number of VAV unit dampers that are fully open at the same time ranges from two (2) to five (5). If less than two (2) or more than five (5) dampers are fully open simutaneously for a significant portion of time, a SAP reset policy may not be present or functional.
If a non-functional or absence of a SAP reset policy is suspected, there are two likely scenarios: If less than two (2) dampers are fully open simutaneously for a significant portion of time, there may be excess supply air pressure - it is recommended to decrease the supply air pressure setpoint.
If more than five (5) dampers are fully open simutaneously for a significant portion of time, there may be inadequate supply air pressure - it is recommended to increase the supply air pressure setpoint.
NOTE: Only operating time is considered in this analysis, which ranges from Monday - Friday and 8 am - 6pm.
Example Delta Air Temperature chart with faulty cooling coil valve.
Too few open dampers! ❌

Observed: Less than two (2) VAV dampers are fully open simutaneously for a significant portion of time.

Recommendations: Decrease the supply air pressure setpoint.

Example Delta Air Temperature chart with no faults.
Just right! ✅

Observed: Two (2) to five (5) VAV dampers are fully open simutaneously for a significant portion of time.

Recommendations: None.

Example Delta Air Temperature chart with faulty heating coil valve.
Too many open dampers! ❌

Observed: More than five (5) VAV dampers are fully open simutaneously for a significant portion of time.

Recommendations: Increase the supply air pressure setpoint.

The Health Index is calculated as the combined fraction of time that two (2), three (3), four (4), and five (5) VAV unit dampers are fully open simutaneously. A higher Health Index indicates a present and functional supply air pressure reset policy.
For example, if two (2) VAV dampers are fully open simutaneously for 40% of the time, three (3) for 35% of the time, four (4) for 5%, and five (5) for 1%, then the Health Index shall be 81%.
NOTE: Only operating time is considered in this analysis, which ranges from Monday - Friday and 8 am - 6pm.
Example Outdoor Air Ratio chart with too much outdoor air.

The Fully Open Dampers chart was generated by summing the number of fully open VAV unit dampers at each timestep. Due to the non-binary nature of the data (i.e., damper position represented as a variable rather than OPEN or CLOSED), a damper is considered fully open when its damper position meets or exceeds 90%. The proportion of time that a certain number of dampers are fully open simutaneously is set relative to the total operating time as of the most recent analysis. Operating time is considered as Monday through Friday, inclusively, and from 8 am to 6pm.