Trane Symbio 210 Installation, Operation And Maintenance Manual page 50

Calibration, Operation Modes, and Control
Setpoint Minimum, space temperature is allowed to drift downward, in the deadband between the active
cooling setpoint and active heating setpoint.
When the space temperature drops below the active heating setpoint, the air valve opens to the Airflow
Setpoint Reset Minimum Local Heat and the SCR controls the electric heater to maintain space
temperature at the active heating setpoint. SCR control is dependent on the degree that the space
temperature is below the active heating setpoint and the amount of time that the space temperature has
been below the active heating setpoint.
If the discharge air temperature reaches the Discharge Air Temperature Design Setpoint, the air valve
opens further and modulates between Airflow Setpoint Reset Minimum Local Heat and Airflow Setpoint
Reset Maximum Local Heat to maintain space temperature at the active heating setpoint, while the SCR
controls the electric heater to maintain discharge air temperature at the Discharge Air Temperature
Design Setpoint (see figure below). If the air valve reaches Airflow Setpoint Reset Maximum Local Heat,
the SCR controls the electric heater to maintain space temperature at the active heating setpoint, while
the air valve remains at Airflow Setpoint Reset Maximum Local Heat.
Figure 8. Single Duct VAV Unit with Modulating Hot Water or SCR Electric Heat
Reheat de-energizes when the space temperature rises more than 0.5°F (0.28°C) above the heating
setpoint. When reheat is de-energized, the cooling Airflow Minimum Setpoint is enforced.
The Trane VAV unit's SCR electric heater module takes a 0-to-10 Vdc control signal from AO2. Any
signal less than 0.2 Vdc, and the heater is turned off. For a signal between 0.2 and 10 Vdc, the heater is
on and modulated up to 100% capacity.
Important: Discharge air temperatures should not exceed between 100°F and 110°F, with a
Table 16. Local heat only with no fan present
Configuration
Local
PWM electric
(1 to 3 stages)
SCR electric
On/Off electric
(1 to 3 stages)
50
temperature between 85°F and 95°F being optimal for space temperature control. If air that
is too hot is delivered to the space through ceiling-mounted diffusers, and then leaves the
space through ceiling-mounted return-air grilles, the buoyancy of this hot air will tend to
cause some of the air to bypass from the supply-air diffusers to the return-air grilles,
resulting in uneven air distribution and possible comfort complaints. Refer to and for fan
powered reheat.
Remote
Not applicable
•
•
•
Not applicable
•
•
•
Not applicable Local thermostatic:
•
•
Each stage represents an equal percentage of total capacity. Total capacity is limited by
communicated supply heat control.
Method of Control
Stage 1
Local PI capacity loop
Each stage represents an equal percentage of total capacity PWM Output (one stage =
100%; two stages = 50% each; three stages = 33.33% each)
Total capacity is limited by communicated supply heat control
Not applicable
Local PI capacity loop
SCR heat capacity =
total capacity
Total capacity limited by
communicated supply
heat control
Local thermostatic:
On: Zt < HSP • On: Zt <HSP - 1°F
(0.56°C)
Off: Zt ≥ HSP + 0.5 °F
(0.28°C) • Off: Zt ≥ HSP - 0.5°F
(0.28°C)
Stage 2 Stage 3
Not applicable
Local thermostatic:
• On: Zt < HSP - 2°F
• Off: Zt ≥ HSP - 1.5°F
(16.9°C)
BAS-SVX091A-EN