58 | INTRODUCTION
Four-W
ay Ceiling Cassette System Engineering Manual
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Method 5: Decoupled Dedicated Outdoor Air System (DDOAS)
Provide a separate, dedicated outdoor-air system designed to filter, condition, and dehumidify ventilation air and deliver it directly to the
conditioned space through a separate register or grille. This approach requires a separate independent ventilation duct system not
associated with the Duct-Free Split system.
Advantages
•
May be used with the full lineup of Duct-Free Split system indoor
units.
•
The outdoor air unit may supply “neutral” air to the occupant space
even when the Duct-Free Split system indoor unit fan changes
speed or cycles on and off. DDOAS controls do not have to be
interlocked with the Duct-Free Split system.
•
In lieu of installing localized smaller outside air treatment
equipment throughout the building, this method centralizes the
ventilation air source making service and filter changes easier and
less disruptive for the building occupants.
•
Third-party demand control ventilation controls are more readily
accommodated.
Disadvantages
•
Ceiling space is required to accommodate ductwork between the
outdoor air unit and ceiling diffusers.
LG recommends using the DDOAS method in all installations.
Outdoor
Air Unit
Indoor Unit
s
Ceiling Diffuser
Indoor Unit
Figure 35: Decoupled Dedicated Outdoor Air System (DDOAS).
BUILDING VENTILATION DESIGN GUIDE
Methodology illustrations are for examples only and do not depict actual
indoor units for the specific outdoor unit pairing. These are generic illus
-
trations to show ventilation design only.