Trane Symbio 210 Installation, Operation And Maintenance Manual page 56

Calibration, Operation Modes, and Control
outdoor air temperature is more than 48°F (8.88°C) below the discharge air temperature setpoint, the
controller cannot provide the requested control performance.
The controller provides no cooling capacity. If the outdoor air temperature (OAT) is above the discharge
air temperature setpoint, the discharge air temperature cannot be controlled and the discharge air
temperature is equal to the OAT.
Staged Hot Water Reheat Control
the coil does not exceed 140°F (60°C). Since only one stage of hot water reheat is available, staged hot
water does not allow tight control of the discharge air temperature. Although the controller operates in
this configuration, it is not recommended.
Staged Reheat Control Algorithm (Integral Only)
An incremental form of the integral PID algorithm computes the desired level of reheat capacity. The
algorithm is run once every 10 seconds.
Modulating Reheat Control (Hot Water Only)
Units equipped with hot water coils should be sized so the maximum temperature of air leaving the coil
does not exceed 140°F (60°C). If hot water reheat is installed, the preferred method of control is with a
modulating valve. The modulating valve enables an instantaneous discharge air temperature within the
dead band of the discharge air temperature setpoint. The reheat capacity algorithm for modulating hot
water discharge air temperature control is the same algorithm used to control modulating hot water
valves for a space temperature controller.
Modulating Reheat Control Algorithm (Proportional-Integral)
An incremental form of the proportional integral algorithm runs once every 10 seconds and calculates
the reheat capacity required to meet the discharge air temperature setpoint. The required capacity is
equal to valve position.
Freeze Protection (Hot Water Only)
Units with hot water coils installed are susceptible to freezing. It is important to prevent the water coils
from freezing. Freeze protection occurs only when the controller is in the OFF state or during the
unoccupied period when the supply air valve is closed and the reheat is disabled. During occupied
operation, the control algorithm indirectly provides freeze protection. Refer to the following table for
unoccupied VFC control.
Controller
Operation
Networked and
valid
communicated
supply air
temperature
Stand-alone,
coil
temperature
sensed at
discharge air
temperature
(a)
Stand-Alone Controller Freeze Protection
Controllers operating without communications do not have the source temperature available to them. In
these cases, the discharge air temperature sensor is assumed to provide a reasonable representation
of the coil temperature at conditions with no airflow, if the sensor is close to the coil. If the discharge air
temperature (at no airflow) falls below the configured outdoor air low limit, the hot water valve is fully
opened. The hot water valve remains OPEN until the discharge air temperature is 10°F above the
configured outdoor air low limit or occupied operation begins. If the communicated source temperature
56
Air Valve
Position Condition
Closed no Communicated supply air temperature greater than configured outdoor air low
flow limit.
Communicated supply air temperature less than or equal to configured
outdoor air low limit, freeze protection active diagnostic (with 10°F hysteresis).
Closed no Discharge air temperature greater than configured outdoor air low limit.
flow
Discharge air temperature less than or equal to configured outdoor air low
limit, freeze protection active diagnostic (with 10°F hysteresis).
(a)
Place the discharge temperature sensor in close proximity to the hot water coil discharge. The sensor effectively reports coil temperature
when there is no airflow through the coil. Therefore, the coil can be freeze protected by the discharge air temperature sensor.
Hot Water
Valve
Position
Closed
Open to 100%
Closed
Open to 100%
BAS-SVX091A-EN