BAS-SVX62E-EN
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Calibration, Operation Modes, and Control
Space Temperature Control (STC) for Single Duct and Fan-powered
Units
Single Duct Units
Space Temperature Control Mode
Space temperature control is one of three supported control algorithms (the other two supported
control algorithms are
“Ventilation Flow Control (VFC),” p. 45
and
Space temperature control requires a valid space temperature. If there is no valid space
temperature (either communicated, local, or default), the space temperature control algorithm
does not run and the unit either shuts down or goes into construction mode.
The controller heat/cool mode is determined by either a communicated request or by the controller
itself. When the heat/cool mode request is AUTO, the controller compares the space temperature
with the active space setpoint to determine the heat/cool mode status.
In addition, the controller compares the active space temperature setpoint and the active space
temperature and calculates the desired capacity need to bring the space temperature up or down
to the space temperature setpoint. The controller positions the modulating air valve to deliver the
required airflow based on cooling or heating capacity required.
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 temperature
setpoint. Based on the controller occupancy mode, the active space temperature setpoint is
determined based on the occupied or standby offset being added to the communicated, local or
default setpoint, the occupied standby cooling setpoint, or the unoccupied cooling setpoint is used.
The outputs are controlled based on the unit configuration and the required cooling capacity. At
0% required cooling capacity, the air valve is 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 that is used to control the volume of airflow through the
diffusers and into the space. Modulating the volume of air modulates the unit cooling capacity.
Heating Operation
Under space temperature control during the heating mode (heat/cool mode is heat the space
temperature is below the active space temperature setpoint and the heat cool mode request is
AUTO), the controller attempts to maintain the space temperature at the active space temperature
setpoint. Based on the controller occupancy mode, the active space temperature setpoint is
determined based on the occupied or standby offset being subtracted from the communicated,
local or default space temperature setpoint or the unoccupied heat setpoint is used. 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 heating minimum or local heating minimum flow
setpoint. As the required heating capacity increases, the air valve opens above its minimum
position. At 100% required heating capacity, the air valve opens to its maximum position.
