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Due to our policy of continuous product innovation, some specications may change without notication.
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52 | FOUR-WAY CASSETTE
Four-Way Ceiling Cassette System Engineering Manual
Method 3: Unconditioned Outdoor Air Ducted to Indoor Units
Untreated outdoor air is channeled through a duct system that is piped to the return air duct on Duct-Free Split system ducted indoor units or
to the frame of Duct-Free Split system four-way cassettes.
Advantages
• May require less ductwork if indoor units are
placed near outdoor walls or a roof deck.
• Controls must be interlocked to shut off the
outdoor air supply fan when the space is
unoccupied.
• Third-party demand-control ventilation
controls may be installed to regulate outdoor
intake based on the CO
2
levels of the
occupied space.
Disadvantages
• Fan(s) will be required to push outdoor air to the indoor unit to overcome the additional
static pressure.
• Filter required to be added to the outdoor air duct.
• Ducted and four-way cassette models are the only indoor units that accept the connection
of an outdoor air duct to the unit case.
• In most cases, in lieu of using the factory mounted return-air thermistor on indoor units, a
remote wall temperature sensor or zone controller will be needed to provide an accurate
reading of the conditioned area temperature.
• Unconditioned outdoor air may affect indoor unit performance, which may necessitate
oversizing the indoor unit.
Outside air may ow backward through the return air-lter grille when the indoor unit fan speed slows or stops in response to changes in the
space load. This may result in captured particulate on the lter media being blown back into the conditioned space.
OA Wall Cap
Damper
Inline Fan
with Filter
Figure 30: Unconditioned Outdoor Air Ducted to Indoor Units.
BUILDING VENTILATION DESIGN GUIDE
Methodology illustrations are for examples only and do not depict actual
indoor units for the specic outdoor unit pairing. These are generic illus-
trations to show ventilation design only.
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