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Method 4: Unconditioned Outdoor Air (Non-Ducted, Fan Assisted Ventilation)
When approved by local codes, the fan assisted ventilation method uses exhaust fans to remove air from the building, and outdoor air is
drawn into occupied spaces through a wall louver or gravity roof intake hood. Supply fans can also be used to push the outdoor air into the
space and building positive pressure will vent the exhaust air through louvers or roof-mounted exhaust hoods. Outdoor air is neither cooled
nor heated before entering the building.
Advantages
• Outdoor air may be manually controlled by the occupant or auto-
matic controls may be installed to open/close outdoor air dampers
or to turn on/off ventilation fans.
• Useful for large open spaces like warehouses, garages, and
workshops.
• Outdoor air volume is a known quantity. Air loads may be easier to
calculate since fans will regulate the amount of outdoor air.
• May be used with a full lineup of Multi V indoor units.
Method 5: Coupled Dedicated Outdoor Air (CDOA)
A separate, dedicated outdoor air system delivers air directly to a Multi V indoor unit or to the return air duct system. After mixing with the
return air stream, ventilation air passes through the indoor unit and into the conditioned space. The pretreatment system is capable of
filtering, conditioning, and dehumidifying outdoor air to room neutral conditions.
Advantages
• Separate ceiling registers or grilles for intro-
duction of the outside air to the conditioned
space may be avoided.
BUILDING VENTILATION DESIGN GUIDE
Disadvantages
• Ducted, 1-way, and 4-way cassette indoor units are the only models designed for direct
connection of an outside air duct.
• The building occupant may not notice the outdoor air pretreatment system has malfunc-
tioned until the unconditioned outdoor air exceeds the indoor unit mixed air limits of 59°F
DB for heating and 76°F WB for cooling.
• If the coil entering air condition limitation is exceeded, the indoor unit may malfunction
and ceases to operate.
• If the outdoor air unit cooling or heating system fails, the malfunction may be masked by
the indoor unit ramping up operating parameters to compensate for the failure.
• Motorized dampers may be required to prevent outdoor air from entering the indoor unit
while the indoor unit has cycled off.
• An LG Dry Contact adapter is necessary to interlock the motorized damper with the
indoor unit fan operation.
• In lieu of using the factory mounted return-air thermistor, a remote wall temperature
sensor or zone controller may be required to provide an accurate conditioned space
temperature reading.
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Disadvantages
• In some locations of the country, it may be difficult to control
humidity levels while outdoor air louvers/hoods are opened.
• Thermal comfort levels may be substandard when louvers/hoods
are opened.
• Indoor units may have to be oversized to account for the added
heating/cooling loads when louvers/hoods are open.
• Hot, cold, and/or humid areas may be present if the outdoor air is
not evenly distributed to the different spaces.
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