Trane Symbio 210 Installation, Operation And Maintenance Manual page 55

Occupancy
Mode
Occupied,
Occupied
Standby, or
Occupied
Bypass
Unoccupied
The ventilation flow control process is a constant volume, variable temperature process. Single duct
VAV units with either electric or hot water reheat are used. Fan-powered units are not used for
ventilation flow control. Ventilation flow control must have a temperature sensor that is located and
setup as a discharge air temperature sensor. The required range of discharge air temperature setpoints
is from 19°F to 70°F (-7.22°C to 21.11°C).
Ventilation flow control staged reheat control (electric or hot water) achieves a 30-minute average
discharge air temperature to within ±5°F (±2.78°C) of the discharge air temperature setpoint when the
inlet temperature is within the control range. Ventilation flow control modulating reheat control (hot water
only) achieves a discharge air temperature to within ±5°F (±2.78°C) of the discharge air temperature
setpoint when the inlet temperature is within the control range.
Air Valve Control
Ventilation flow control uses the air valve as a constant volume device. The unit is given a constant flow
setpoint for air valve control (configured ventilation setpoint). The air valve only repositions itself in
response to changes in inlet static pressure. By using pressure-independent control for ventilation
purposes, a constant volume of fresh air can be maintained, regardless of small fluctuations in inlet
static pressure. Ventilation flow control unit can use a Ventilation Setpoint from a BAS system, if it is
valid. If the unit is standalone, the ventilation flow control uses one of the following two (2) airflow
setpoints:
•
•
Staged Reheat Control (Electric and Hot Water)
The heat outputs of the controller are binary. Only discrete levels of discharge air temperature are
possible. Since discrete discharge air temperature levels do not always provide an instantaneous
temperature within the required band, staged reheat controls to a 30-minute average discharge air
temperature. The discharge air temperature setpoint is limited from 19°F to 70°F (-7.22°C to 21.11°C).
Staged Electric Reheat Control
Units that are equipped with electric reheat should be sized so that the maximum temperature rise
across the heating elements is from 40°F to 48°F (4.44°C to 8.88°C); it should never exceed 50°F (10°
C) for safety reasons. These values were selected to allow the largest control range without damage to
the heater elements.
For staged electric ventilation flow control, the number of installed stages can range from one to three.
Three stages are recommended, since finer control is available with more stages. In cases where the
BAS-SVX091A-EN
Source Temperature
Communicated source temperature (if
valid; if not valid, discharge air
temperature) greater than configured OA
low limit.
Communicated source temperature (if
valid; if not valid, discharge air
temperature) less than configured OA
low limit.
If no reheat being used, it uses the configured Ventilation Setpoint Local.
If reheat being used, it uses the configured Airflow Setpoint Minimum Local Heat.
Calibration, Operation Modes, and Control
Air Valve Control
Constant volume (if
valid,
communicated
ventilation setpoint;
if not valid,
Any
configured
ventilation setpoint)
Closed, 0%
Closed, 0%
Reheat Control
Electric VFC staged reheat
control
Staged hot water VFC staged reheat
control
VFC modulating
reheat control
Modulating hot
(same as STC
water
capacity control)
Electric Off
Staged hot water Off
Modulating hot Off
water
Electric Off
Staged hot water On, 100% freeze
protection
Modulating hot On, 100% freeze
water protection
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