VAV-SVX07F-EN 41
Calibration, Operation Modes, and Control
Figure 6. 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-t
o-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: D
ischarg
e air temperatures should not exceed between 100°F and 110°F, with a
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 Table 9 and Table 10, p. 42 for fan powered reheat.
Table 9. Local Heat Only With No Fan Present
Configuration Method of Control
Local Remote Stage 1 Stage2 Stage 3
PWM electric
(1 to 3 stages)
Not applicable
• 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
SCR electric Not applicable
• Local PI capacity loop
• SCR heat capacity = total capacity
• Total capacity limited by
co
mmunica
ted supply heat control
Not applicable Not applicable
On/Off electric
(1 to 3 stages)
Not applicable
Local thermostatic:
•On: Zt < HSP
• Off: Zt HSP + 0.5 °F (0.28°C)
Local thermostatic:
• On: Zt <HSP - 1°F (0.56°C)
• Off: Zt HSP - 0.5°F (0.28°C)
Local thermostatic:
•On: Zt < HSP - 2°F
• Off: Zt HSP - 1.5°F (16.9°C)
Each stage represents an equal percentage of total capacity. Total capacity is limited by communicated
supply heat control.
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