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RT-PRC031-EN 23
Applications Considerations
The Trane 100 percent modulating
exhaust system with Statitrac
provides efficient control of building
pressure in most applications simply
because 100 percent modulating
exhaust discharge dampers (or VFD)
are controlled directly from building
pressure, rather than from an indirect
indicator of building pressure, such
as outdoor air damper position.
100 Percent Modulating Exhaust
System without Statitrac,
Constant Volume Units Only
This fan system has performance
capabilities equal to the supply fan.
The FC exhaust fans are started by
the economizer's outdoor air damper
position and the exhaust dampers
track the economizer outdoor air
damper position. The amount of air
exhausted by this fan is controlled by
modulating discharge dampers at the
fan outlet. The discharge damper
position is controlled by a signal that
varies with the position of the
economizer dampers. When the
exhaust fans start, the modulating
discharge dampers are fully closed,
and exhaust airflow is 15 to 20
percent of total exhaust capabilities.
Advantages:
• The exhaust fan runs only when
the economizer reaches the
desired exhaust enable point.
• Exhaust dampers are modulated
based on the economizer
position.
• The exhaust fan discharges in a
single direction resulting in more
efficient fan operation compared
to return fan systems.
• When discharge dampers are
utilized to modulate the exhaust
airflow, the exhaust fan may be
running unloaded whenever the
economizer dampers are less
than 100 percent open.
The Trane 100 percent modulating
exhaust system provides excellent
linear control of building exhaust in
most applications where maintaining
building pressure is not important.
100 Percent Modulating
Return Fan Systems with
Statitrac™ Control, Constant
Volume and VAV units
For both CV and VAV applications,
the IntelliPak II air handler offers 100
percent modulating return fan
systems. A differential pressure
control system, Statitrac, uses a
differential pressure transducer to
compare indoor building pressure to
atmospheric pressure. The return fan
exhaust dampers are modulated,
based on space pressure, to control
the building pressure to within the
adjustable, specified deadband that
is set at the Human Interface Panel. A
VFD modulates the return fan speed
based on return duct static pressure.
Economizer and return air dampers
are modulated independent of the
exhaust dampers based on
ventilation control and economizer
cooling requests.
Advantages:
• The return fan operates
independently of the supply fan
to provide proper balance
throughout the airflow envelope.
• Statitrac compensates for
pressure variations within the
building from remote exhaust
fans and makeup air units.
• The return fan acts as both
exhaust and return fan based on
operation requirements.
The Trane 100 percent modulating
return system with Statitrac provides
efficient control of building pressure
in applications with higher return
duct static pressure and applications
requiring duct returns.
Exhaust discharge dampers are
controlled directly from building
pressure, return fan VFD is controlled
from return static pressure, and
return/economizer dampers are
controlled based on ventilation
control and economizer cooling
requests. 100 Percent Modulating
Return Fan without Statitrac™
Control, Constant Volume Units Only
The exhaust discharge dampers are
modulated in response to building
pressure. The return fan runs
continuously while the supply fan is
energized.
Economizer and return air dampers
are modulated independent of the
exhaust dampers based on
ventilation control, and economizer
cooling requests.
Advantages:
• The exhaust dampers are
modulated as needed through a
space pressure sensor input to
maintain building pressure.
• The return fan discharges in two
directions, thereby balancing
exhaust and unit return air
volumes.
Supply and Return Airflow
Configurations
The typical air handler installation
has both the supply and return air
paths routed through the roof curb
and building roof. However, many air
handler installations require
horizontal supply and/or return from
the air handler because of a
building's unique design or for
acoustic considerations.
With IntelliPak II, there are several
ways to accomplish horizontal
supply, see Table 1, p. 24 and/or
return, see Table 2, p. 24.