NEED AHU (BV1)
The Need AHU Start value object is set to TRUE (1) for any of the following conditions.
l The system mode is UNOCCUPIED and the Cooling loop or the Heating loop is
greater than 100% for longer than 10 minutes.
l The system mode is OCCUPIED or STANDBY.
l Either of the Motion Override or Local Override variable objects are TRUE (1).
The Need for AHU Start object changes to FALSE (0) when both loops drop below 5% and
the system mod is not OCCUPIED or STANDBY and both override variable objects are
FALSE (0).
NEED COLDER SUPPLY (BV2)
The Need Colder Supply value object is set to TRUE (1) when the system mode is
STANDBY or OCCUPIED and the Cooling loop is greater than 95% for 30 minutes. The
indicator changes to FALSE (0) when the Cooling loop falls below 90% or when the system
mode is UNOCCUPIED.
NEED MORE STATIC (BV3)
The Need More Static value object is set to TRUE (1) when the controller has attempted to
drive the damper fully open for longer than 2 minutes 30 seconds and any of the following are
TRUE (1).
l The system mode is OCCUPIED or STANDBY.
l Either of the Motion Override or Local Override variable objects are TRUE (1).
When any of these conditions are no longer true, the indicator changes to FALSE (0).
NEED HOTTER SUPPLY (BV7)
The Need Warmer Supply value object is set to TRUE (1) when the system mode is
STANDBY or OCCUPIED and the Heating loop is greater than 95% for 30 minutes. The
indicator changes to FALSE (0) when the Heating loop falls below 90% or when the system
mode is no longer OCCUPIED.
Damper operation
Damper movement is determined by comparing the actual airflow reading to the airflow
setpoints. If the actual airflow is within 5% of the setpoint, no damper action is initiated.
Once within the 5% deadband, the actual airflow must be outside a 7% deadband before
damper position changes.
To improve stability near setpoint, the damper motor is pulsed when the actual flow rate is
within 15% of the requested flow rate. The pulse rate is 5 seconds and the duty cycle is
controlled by analog variable MOTOR PAUSE. In addition, the motor will pause for 10
seconds before the damper changes direction.
SimplyVAV Section 7: Sequences of operation
Revision H 55
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