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RT-SVX073A-EN
Space Static Pressure Control without
Statitrac™
If Statitrac™ is not installed, or the space static pressure
sensor has failed, space static pressure control without
Statitrac
TM
becomes active. The relief damper will track to
the outdoor air damper position and the relief fan speed will
track to the relief damper position when the supply fan is
proven On and the outdoor air damper position is greater
than the relief enable position setpoint.
Space static pressure control operation will be terminated
whenever any of the activation conditions are not true,
when the outdoor air damper is fully closed or when the
outdoor air damper is less than the relief enable point
minus 10%.
If the relief fan or damper is in failure, the relief fan will be
commanded Off and the relief damper will be commanded
Closed.
0-25% Motorized Outdoor Air Damper
The outdoor air damper will drive open to a position
between 0 and 25% position set from the user interface
when the supply fan turns on during occupied periods. It is
driven closed when the fan is turned off or during
unoccupied periods. The following options and functions
are disallowed with 0-25% Motorized Outside Air Damper:
• Economizing
• Fresh Air Measurement
• OA CFM Compensation (VAV units)
• Relief fan
• Space Pressure Control
• Supply Air Low Limit
• Return Fan
• Energy Recovery
• Demand Controlled Ventilation
• Ultra-Low Leak Damper Option
Units Without a Return Air Damper
For units without a Return Air Damper, special
consideration of the outdoor air damper is required. The
only airpath for supply fan operation will be provided via the
outdoor air damper. If this damper fails, the supply fan
operation must be terminated immediately. Additionally, to
support proper airflow, the outside air damper must be
opened prior to the supply fan being allowed to start. The
following options and functions are disallowed when units
are configured without a Return Air Damper:
• DCV
• TRAQs
• Economization
• OA Compensation
• Ventilation Override Mode
• Emergency Override
• External Capacity Control
• Return/Relief fans with and without bypass
• Statitrac
• Ultra-low Leak dampers
• Energy Recovery Wheel
• Rapid Restart
Units With Independent Return Air
Damper Control
All units complying with agency (Title 24) requirements
and/or units configured with energy recovery option, need
independent control of the return air damper relative to the
normal outdoor air damper mechanical linkage
arrangement of other units. This requires a dedicated
actuator and control scheme. The behavior of this
configuration utilizse the same 0-100% command to the
outdoor air damper mapping it also to the return air damper
actuator. For the outdoor air damper 0% equates to fully
closed and 100% is fully opened. To satisfy this one
command control for both dampers, the 0% command for
the return damper equates to fully open and 100%
command equates to fully closed.
Energy Recovery Wheel
The primary components of the energy recovery system
are the energy recovery wheel, relief air bypass damper,
outdoor air bypass damper, and the energy recovery
preheat output. See “Energy Recovery Wheel ,” p. 70 and
Figure 38, p. 72
Filter and differential pressure sensors are also placed
between the wheel and the outdoor air damper. An
adjustable setpoint is provided at the user interface. When
the measured pressure exceeds this setpoint a diagnostic
will be generated to notify the user when that filter needs to
be changed. The differential pressure is only valid when the
outdoor air bypass damper is fully closed.
When the energy recovery wheel is not operational,
including when the unit is powered off, both bypass
dampers are driven open. Both dampers actuate from a
command of 0% to 100% where 0% equates to fully open
(minimum capacity) and 100% equating to fully closed
(maximum capacity). The energy recovery wheel is only
energized when both the Supply Fan and Relief Fan are
requested on by the various functions that control them.
Energy recovery is a passive function and does not request
fan operation. Once the required airflow is present, the
wheel is commanded on if the indoor vs. outdoor conditions
are such that energy can be recovered. This is assessed
differently in cooling and heating modes.
Unit Startup
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