Trane IntelliPak WEHE Series Installation, Operation And Maintenance Manual page 13

setpoint based on the space temperature and/or humidity
conditions. Concurrently, the unit will control and optimize
the supply fan speed to maintain the zone temperature to
a zone temperature setpoint.
Supply Fan Output Control
Units configured for Single Zone VAV control will utilize
the same supply fan output control scheme as on
traditional VAV units except the VFD signal will be based
on zone heating and cooling demand instead of the supply
air pressure.
VFD Control
Single Zone VAV units will be equipped with a VFD-
controlled supply fan which will be controlled via a 0-
10VDC signal from the Rooftop Module (RTM). With the
RTM supply fan output energized and the RTM VFD output
at 0VDC, the fan speed output is 37% (22Hz) from the VFD
by default; and at 10VDC the fan speed output is 100%
(60Hz). The control scales the 0-10VDC VFD output from
the RTM linearly to control between the 37-100% range.
The VFD will modulate the supply fan motor speed,
accelerating or decelerating as required to maintain the
zone temperature to the zone temperature setpoint. When
subjected to high ambient return conditions the VFD will
reduce its output frequency to maintain operation. Bypass
control is offered to provide full nominal airflow in the
event of drive failure.
Ventilation Control
Units configured for Single Zone VAV control will require
special handling of the OA Damper Minimum Position
control in order to compensate for the non-linearity of
airflow associated with the variable supply fan speed and
damper combinations. Units configured for TRAQ with or
without DCV will operate identically to traditional units
with no control changes.
Space Pressure Control
For units configured with Space Pressure Control with or
without Statitrac, the new schemes implemented for
economizer minimum position handling require changes
to the existing Space Pressure Control scheme in order to
prevent over/under pressurization. The overall scheme
will remain very similar to VAV units with Space Pressure
Control with the exception of the dynamic Exhaust Enable
Setpoint.
For SZVAV an Exhaust Enable Setpoint must be selected
during the 100% Fan Speed Command. Once selected, the
difference between the Exhaust Enable Setpoint and
Design OA Damper Minimum Position at 100% Fan Speed
Command will be calculated. The difference calculated will
be used as an offset and added to the Active Building
Design OA Minimum Position Target in order to calculate
the dynamic Exhaust Enable Target, which will be used
throughout the Supply Fan Speed/OA Damper Position
range.
RT-SVX35H-EN
The Exhaust Enable Target could be above or below the
Active Building Design OA Minimum Position Target
Setpoint, based on the Active Exhaust Enable Setpoint
being set above or below the Building Design Minimum
Position at 100% Fan Speed Command. Note that an
Exhaust Enable Setpoint of 0% will result in the same effect
on Exhaust Fan control as on VAV applications with and
without Statitrac.
Occupied Cooling Operation
For normal cooling operation, cooling capacity will be
staged or modulated in order to meet the calculated
discharge air target setpoint. If the current active cooling
capacity is controlling the discharge air within the
deadband, no additional cooling capacity change will be
requested. As the Discharge Air Temperature rises above
the deadband, the algorithm will request additional
capacity as required (additional compressors or
economizer). As the Discharge Air Temperature falls below
the deadband, the algorithm will request a reduction in
active capacity.
Default Economizer Operation
By default, the unit will be setup to optimize the minimum
supply fan speed capability during Economizer Only
operation. If the economizer is able to meet the demand
alone, due to desirable ambient conditions, the supply fan
speed will be allowed to increase above the minimum
prior to utilizing mechanical cooling if discharge air
setpoint falls below the discharge air Lower Limit
(Cooling) setpoint.
Unoccupied Mode
In Unoccupied mode the unit will utilize setback setpoints,
0% Minimum OA Damper position, and Auto Fan Mode
operation as on normal CV units. The Supply Fan speed,
and cooling and modulating types of heat, will be
controlled to the discharge air target setpoint as is done
during occupied periods. The Supply fan speed during
staged heat control will be forced to 100% as on normal CV
units.
Occupied Heating Operation
Occupied heating operation has two separate control
sequences; staged and modulated. All staged heating
types will drive the supply fan to maximum flow and stage
heating to control to the Zone Heating Setpoint. For units
with Hydronic and Gas heat, modulated SZVAV Heating.
On an initial call for heating, the supply fan will drive to the
minimum heating airflow.
On an additional call for heating, the heat will control in
order to meet the calculated discharge air target setpoint.
As the load in the zone continues to request heat
operation, the supply fan will ramp-up while the control
maintains the heating discharge air temperature. Heating
can be configured for either the energy saving SZVAV
Heating solution as described above, or the traditional,
less efficient CV Heating solution.
General Information
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