Variable Air Volume Applications; Vav); Supply Fan Output Control; Minimum Supply Fan Output - Trane Voyager Commercial Installation, Operation And Maintenance Manual

S S t t a a r r t t u u p p
conditions must be met as described above for
entering and leaving Tempering operation.
CV Units with Modulating Heat
On units with Modulating Gas Heat, Supply Air
Tempering is inherent to the Modulating Heat design
and does not require any additional configuration/
enabling. Modulating Heat Tempering is accomplished
by allowing the unit to return to heating if the Zone is
marginally satisfied and the Supply Air temperature
begins to fall. The following conditions must be true to
enable the unit to perform "Tempering":
• The supply fan is ON.
• The unit is in Occupied mode.
• Zone Temp. is less than the active Cooling setpoint.
• The unit is in Heat mode but is not actively heating
OR
• The unit is in AUTO-COOL mode but not actively
cooling and cooling capacity has been OFF for 5
minutes.
Once the above conditions are met, and the supply air
temperature drops below the ZHSP - 10°F, the unit will
transition back into active heating operation and will
begin to control the modulating heat output to
maintain the supply air temperature.
Once the unit has entered into Tempering mode, the
unit will leave active heating either by normal heat
termination as determined by the heating control
algorithm or when the Zone Temperature reaches the
active ZCSP.
SZ VAV Units with Staged Heat
For SZ VAV units configured with a Staged Heating
type, the Supply Air Tempering function will operate as
on a CV unit with Staged Heat.
SZ VAV Units with Modulating Heat
For units configured with a Modulating Heat type,
"Tempering" is an extension of normal Heating control
which allows a transition from inactive "Auto-Cool"
mode to Heating based on supply air temperature if the
Zone Temperature is in control. The following
conditions must be true to allow the unit to enter
Supply Air Tempering:
• Supply Fan is ON.
• The unit is in Occupied mode.
• The unit is operating in Auto-Cool Mode.
• Cooling has been inactive for 5 minutes.
When the above conditions are true, Tempering will be
allowed when the Supply Air Temperature falls below
the user selectable Minimum Supply Air Cooling
Setpoint (minus deadband) as long as the Zone
Temperature is < ZCSP - 1°F. Once the unit transitions
into "Tempering" the unit will transition to normal
heating control and will control the supply air
48
temperature between the minimum and maximum
supply air setpoints.
If the Zone Temperature rises above the ZCSP during
"Tempering" the unit will de-energize Heating and
"Tempering" will be disabled until conditions allow for
it again. Normal Auto-Changeover requirements will be
in control to allow the unit to transition into Active Cool
mode.
Variable Air Volume
Applications (SZ VAV)

Supply Fan Output Control

Units configured for Single Zone VAV will include a
VFD controlled supply fan motor which will be
controlled via the 0-10Vdc Indoor Fan Speed output
located on the RTOM and the RTRM Supply Fan output.
With the RTRM Supply Fan output energized and the
RTOM Indoor Fan Speed output at 0Vdc the fan speed
output is 33% (20Hz) for cooling mode and 58% (35Hz)
for heating modes from the VFD motor and at 10Vdc
the fan speed output is 100% (60Hz). The control will
scale the 0-10Vdc output from the RTOM linearly to
control to 38%-100% controllable range based on the
space heating or cooling demand.

Minimum Supply Fan Output

Refer to the table below for details on minimum supply
fan output signals associated with each unit function.
Note that each value represents the actual Fan Output
%.
Table 25. Fan output - standard efficiency
Function
Ventilation Only
Economizer Cooling
Cool 1 (C1 Energized)
Cool 2 (C1 or C2)
Cool 3 (C1 + C2 Energized)
SZVAV Modulating Heat
CV Staged Heat
SZVAV Modulating Heat
Tempering
CV Staged Heat Tempering
Modulating Reheat
Table 26. Fan output - high efficiency
Function
Ventilation Only
Economizer Cooling
Minimum Fan Output %
58%
58%
58%
67%
67%
58%
100%
58%
100%
80%
Minimum Fan Output %
45%
45%
RT-SVX34R-EN