Trane Symbio 210 Installation, Operation And Maintenance Manual page 48

Calibration, Operation Modes, and Control
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.
All units have a modulating air valve that is used to control how much air is flowing through the diffusers
and into the space. By modulating the volume of airflow, the unit heating capacity is modulated.
Reheat Enable Setpoints
Units may have local or remote reheat, which may be hydronic or electric. Reheat is turned on when the
space temperature is below the active space temperature setpoint, and the supply air temperature is
below the reheat enable setpoint. Reheat is used to maintain the space temperature at the heating
setpoint. Heating operation and Reheat are two different entities.
Auto-changeover
The auto-changeover feature is used if the RTU has heat and the Symbio 500 has a valid local or
communicated Supply Air Temperature. If the supply air temperature reaches the Auto-changeover
Point, then the air valve control changes from cooling control action to heating control action.
In cooling control action, the air valve modulates between the Airflow Setpoint Minimum and Airflow
Setpoint Maximum to meet the required cooling capacity. In heating control action, the air valve
modulates between Airflow Setpoint Minimum Heat and Airflow Setpoint Maximum Heat to meet the
required heating capacity. Essentially, the RTU is providing heat to the space. If the heating capacity
increases, the air valve modulates further open to provide more hot air to the space.
Air Valve Control in Space Temperature Control Operation
Air delivered to the space is controlled with a three-wire, floating-point actuator that modulates the air
valve. The controller positions the modulating air valve to deliver the desired airflow (cooling or heating
capacity).
The desired airflow is called the active flow setpoint. The controller positions the modulating air valve to
deliver the desired airflow (cooling and heating capacity) to within +/-2% of nominal airflow. For
example, if the nominal airflow of the box is 900 CFM, the air valve is controlled to maintain flow within
+/- 18 CFM of the airflow setpoint.
48 BAS-SVX091A-EN