Space Temperature Control: Single Duct Units - Trane VAV VV550 LonTalk Installation & Operation Manual

mode by either communicating an occupancy mode request of bypass mode (communicated
occupancy override) to the controller or by using the zone sensor timed override ON button. The
occupied bypass mode and the occupied mode operate similarly.
When the controller is in the unoccupied mode, pressing the zone sensor ON button places the
controller in the occupied bypass mode for the duration of the configured occupied bypass time.
When the controller is in the occupied standby mode, pressing the zone sensor ON button places
the controller in the occupied bypass mode for the duration of the configured occupied bypass
time.

Space Temperature Control: Single Duct Units

Space temperature control (STC) is one of three supported control algorithms. Space temperature
control requires a valid space temperature. If there is no valid space temperature (communicated
or local), the space temperature control algorithm does not run; the unit either shuts down or goes
to construction mode.
VAV VV550 Controllers use the active space temperature to maintain the space temperature at the
active space cooling setpoint or the active space heating setpoint.
The controller heat/cool mode is determined by either a communicated request or by the controller
itself, when the heat/cool mode is auto. When the heat/cool mode is auto, the controller compares
the primary air temperature with the configured auto-changeover setpoint to determine if the
primary air is hot or cold. This is called autochangeover. This determination may differ from the
reported heat/cool mode, which matches the zone demand.
The control compares the active space setpoint and the active space temperature and calculates
the desired capacity. The control positions the modulating air valve to deliver the desired airflow
(cooling or heating capacity).
Cooling Operation
Under space temperature control during the cooling mode (communicated heat/cool mode is cool),
the controller attempts to maintain the active space temperature at the active space cooling
setpoint. Based on the controller occupancy mode, the active space cooling setpoint is either the
occupied cooling setpoint, the occupied standby cooling setpoint, or the unoccupied cooling
setpoint.
The outputs are controlled based on the unit configuration and the required cooling capacity. At
0% required cooling capacity, the air valve is closed or at the active minimum flow setpoint. As the
required cooling capacity increases, the air valve opens above the minimum position. At 100%
required cooling capacity, the air valve opens to the maximum position or to the active maximum
flow setpoint.
All units have a modulating air valve. The modulating air valve is used to control the volume of air
flowing through the diffusers and into the space. Modulating the volume of air modulates the unit
cooling capacity.
Also, units may have local or remote reheat. The reheat may be hydronic or electric. Reheat is
allowed to turn On when the space temperature is below the heating setpoint
Heating Operation
Under space temperature control, during the heating mode (communicated heat/cool mode is
heat), the controller attempts to maintain the space temperature at the active heating setpoint.
Based on the controller occupancy mode, the active space heating setpoint is either the occupied
heating setpoint, the occupied standby heating setpoint, or the unoccupied heat setpoint. All
ventilation requirements are in force during occupied heating and cooling.
The outputs are controlled based on the unit configuration and the required heating capacity. At
0% required heating capacity, the air valve is at its minimum flow setpoint. As the required heating
VAV-SVP01A-EN
Sequence of Operations
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