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.
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