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BUILDING VENTILATION DESIGN GUIDE
Method 2: Unconditioned Outdoor Air (Non-Ducted, Natural Ventilation)
Natural ventilation devices, such as operable windows or louvers may be used to ventilate the building when local code permits. The open
area of a window or the free area of a louver must meet the minimum percentage of the net occupied floor area.
Advantages
• Occupants control the volume of the ventilation air manually.
• Useful for historic buildings that have no ceiling space available for
outdoor air ductwork.
• May be used with the full lineup of Multi V indoor units.
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 Multi V concealed indoor units or to the frame
of Multi V 1-way and 4-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
levels of the
2
occupied space.
108 |
Disadvantages
• In some locations, it may be difficult to control humidity levels when
• Thermal comfort levels may be substandard when windows are
• Indoor units may have to be oversized to account for the added
• Provides outdoor air to perimeter spaces only. Additional mechani-
• Outdoor air loads may be difficult to calculate since the quantity of
• May affect indoor unit proper operation when open.
Disadvantages
• Fan(s) will be required to push outdoor air to the indoor unit. Indoor units are engineered
for low sound levels and are not designed to overcome the added static pressure caused
by the outdoor air source ductwork.
• Ventilation air must be pre-filtered before mixing with the return air stream. LG indoor
cassette models are configured to introduce the ventilation air downstream of the return
air filter media.
• Ducted, 1-way, and 4-way cassette models are the only indoor units that accept the
connection of an outdoor air duct to the unit case.
• Mixed air conditions must be between a minimum of 59°F DB while operating in heating
and a maximum of 76°F WB while operating in cooling. Depending on the ventilation air
volume requirement, the location choices are limited where untreated outside air may be
introduced to the building using this method.
• Larger indoor units may be required to satisfy for additional outdoor air.
• Motorized dampers may be required to prevent outdoor air flow through the indoor unit
when the indoor unit is not operating.
• An LG Dry Contact adapter may be necessary to interlock the motorized damper with the
indoor unit.
• While operating in heating, the untreated outdoor air may delay the start of the indoor unit
fan impacting building comfort.
• 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 for each indoor unit to
provide an accurate reading of the conditioned area temperature.
©
windows are open.
open.
heating and cooling loads when windows are open.
cal ventilation system may be required to satisfy requirements for
interior spaces.
outdoor air is not regulated.

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