When you go to the advanced overrides page for a VAV II/III or IV type UCM, in addition to Present Value, the following fields can be overridden:
Sends an air valve calibration request to the VAV. This request can be done manually or by referencer.
If calibration is manually initiated, the VAV does not recognize the calibration request until this field transitions from Normal to Recalibrate, then stays for at least one minute in Recalibrate before going back to Normal again. If the switch is delayed in being set back to Normal, or if it is left in the recalibrate state indefinitely, the VAV does not calibrate. Additionally, the flow overrides do not function properly.
When a VAV undergoes calibration, it initializes the zero value for the pressure transducer (flow ring) measurements, re-establishes the air valve position, and re-establishes the water valve position if applicable. To re-establish valve position, the VAV over-drives the valve closed for 30 seconds beyond the configured stroke time (water valve for stroke time plus 15 seconds).
A VAV automatically recalibrates after power up or after 15 minutes of communication loss.
Because the unit valve closes during a calibration, calibrating all of the units at the same time could result in high duct pressure. To prevent this problem, the VAVs calibrate at different times from a common calibration start time. In any given group of VAVs, only 25% percent of them are allowed to calibrate at the same time.
Example: Once the calibration flag is set (at time = 0 minutes), the first 25% of a group of VAVs begins the calibration process. Seven minutes later (at time = 7 minutes) the second 25% of the group begins calibration. Seven minutes later (at time = 14 minutes) the third 25% of the group begins calibration. Finally, seven minutes later (at time = 21 minutes) the fourth 25% of the group begins calibration. Depending upon the air valve drive time, the entire calibration process for the group of VAVs could take up to 33 minutes to complete.
The membership of a VAV ll/lll UCM to a calibration group is predetermined. The ICS address of the UCM determines which group the UCM falls into. The list below shows the entire range of VAV UCM ICS addresses divided into four calibration groups.
VAV UCMs can have drive times up to 666 seconds (11.1 minutes). Since UCM resets are staggered by 7 minutes, up to half of the units could potentially be closed at one time during the calibration process.
After a power failure, the calibration start time is delayed until twenty minutes after power is restored. If a recalibrate command has been downloaded from Tracer Summit, the calibration begins immediately according to the address schedule as described above.
Sends a flow override to the UCM that causes the UCM to drive its damper fully open, turn off all unit heat, and disable its parallel fan.
Flow override selections that are not possible due to the priority scheme are unavailable. Also, if multiple flow overrides exist simultaneously, the following priority scheme applies: DRIVE OPEN, DRIVE CLOSED, DRIVE MINIMUM, DRIVE MAXIMUM, AUTO. Both VAS and the VAV editor can provide flow overrides. The VAV editor flow overrides are higher priority.
Sends a flow override to the UCM. This causes the UCM to drive its damper fully closed, turn the unit fan off, and turn the unit heat off.
Flow override selections that are not possible due to the priority scheme are unavailable. Also, if multiple flow overrides exist simultaneously, the following priority scheme applies: Drive Open, Drive Closed, Drive Minimum, Drive Maximum, Auto. Both VAS and the VAV editor can provide flow overrides. The VAV editor flow overrides are higher priority.
Example: If an operator has selected Drive Closed override, the Drive Min and Drive Max override fields are not available because they cannot affect the UCM. The Drive Open override field is still available for use because it can still affect the UCM.
Sends a flow override to the UCM that causes the UCM to drive its damper to its Active Min Flow Setpoint. The Active Min Flow Setpoint is one of the following:
Note: The Active Min Flow Setpoint may not match what appears in the VAV editor if the Setpoint Multiplier is enabled and the Multiplier Value is not equal to one.
Flow override selections that are not possible due to the priority scheme are unavailable (grayed). Also, if multiple flow overrides exist simultaneously, the following priority scheme applies: DRIVE OPEN, DRIVE CLOSED, DRIVE MINIMUM, DRIVE MAXIMUM, AUTO. Both VAS and the VAV editor can provide flow overrides. The VAV editor flow overrides are higher priority.
Example: If an operator has selected the Drive Min override, the Drive Max override field is not available because it is the only override that cannot affect the UCM.
Sends a flow override to the UCM. This causes the UCM to drive its damper to the Max flow setpoint. Electric Heat and Parallel fans are disabled during a max flow override.
Flow override selections that are not possible due to the priority scheme are unavailable (grayed). Also, if multiple flow overrides exist simultaneously, the following priority scheme applies: Drive Open, Drive Closed, Drive Minimum, Drive Maximum, Auto. Both VAS and the VAV editor can provide flow overrides. The VAV editor flow overrides are higher priority.
Automatically, the VAS includes a capability to override its VAV members to maximum if the VAS is in the heat mode and the following check box is selected: Drive VAVs to Max Flow if VAS is Heating.
Example: If an operator has selected Drive Max override, the Drive Min, Drive Closed, and Drive Open override fields are still available for use because they can still affect the UCM.
This field is available for units equipped with a parallel fan.
Use this field to disable the operation of the parallel fan. When a unit's parallel fan is locked out, the UCM does not use its fan or its local electric heat (Staged Electric, Electric Fast Pulse, Electric Slow Pulse).
Shows the state of the terminal heat override. When it is set to Reheat Lockout (either manually or by referencer), the UCM is not allowed to use its terminal heat.
Note: This field is only available when the unit has Staged Hot Water or Proportional Hot Water heat types.
Forces the UCM to turn on all of its hot water outputs or drive open its proportional hot water valve. This may be useful for water system balancing. The UCM maintains the full open condition over power failures. Unit heat must be enabled in order for this condition to be effective. To cancel the full open condition, click to clear the Drive Open Hot Water Outputs/Valve check box.
Only units with the following heat types are affected:
When Setpoint Not Offset is selected, the control offset is not used and the heating and cooling setpoints are not affected. Selecting Setpoint Offset means that control offset is used and the heating and cooling setpoints are offset (added to the cooling setpoint and subtracted from the heating setpoint) by the Control Offset Value.
A referenced binary property in the zero state is interpreted as Setpoint Not Offset, and a referenced binary property in the one state is interpreted as Setpoint Offset.
In UCM software versions 1.0–3.0, the thumbwheel setpoint is not effected if selected as the setpoint source. In version 3.1 and later versions, the setpoint offset is applied to the thumbwheel setpoints.
Regardless of the Control Offset field setting, if the present value of the VAV is demand limit, the VAV applies the control offset value to its heating and cooling setpoint.
If the VAV has been directed to apply a control offset to its heating and cooling setpoints, the value appearing in the Control Offset Value is the offset applied.
The Control Offset Value is added to the occupied cooling setpoint and subtracted from the occupied heating setpoint to determine the occupied mode active setpoints.
Select the control source to enable or disable the Minimum Flow Setpoint Multiplier feature that adjusts the UCM minimum flow setpoint.
If Auto is selected, either manually or by referencer, a multiplier value of 1.0 is sent to the UCM.
If a referenced value is selected, the property must be Enabled to send the edited or referenced multiplier value.
Field set to Auto
Field set to Enabled
Example: The Min Cooling flow setpoint = 1000 CFM (472 L/s). The Multiplier Value = 0.5. With the Minimum Flow Setpoint Multiplier field Enabled, the active minimum cooling flow setpoint would be 0.5 x 1000 CFM (472 L/s) = 500 CFM (236 L/s), assuming for this example that the active minimum flow setpoint is the Min Cooling flow setpoint.
The edited cooling minimum flow/position can be adjusted by applying this multiplier.
In the heating mode, the heating minimum overrides the "adjusted" cooling minimum if it is higher. If the adjusted cooling minimum is higher than the heating minimum and the UCM is in heating mode, the adjusted cooling minimum applies.
If the multiplier = 1.0, the heating minimum always applies while in the heating mode. If the multiplier = 0, the cooling minimum = 0.
Example: The Min Cooling flow setpoint = 1000 CFM (472 L/s). The Multiplier Value = 0.5. With the Minimum Flow Setpoint Multiplier field Enabled, the active minimum cooling flow setpoint would be 0.5 x 1000 CFM (472 L/s) = 500 CFM (236 L/s), assuming for this example that the active minimum flow setpoint is the Min Cooling flow setpoint.