Mammoth 7 to 24 Tons: High Efficiency, Superior IAQ Twin and Quad Circuit Horizontal and Vertical (M-Vintage) - Manual (Page 6)

6
MAMM-WSHP-IOM-1MA (November 2011)
Ductwork and Attenuation
Discharge ductwork is normally used with the M-
vintage horizontal and vertical multiple circuit units.
Return air ductwork may also be required.
All ductwork should conform to industry standards
of good practice as described in the ASHRAE Systems
Guide.
The discharge duct system will normally consist of
a flexible connector at the unit connection, a transition
piece to the full duct size, a short run of duct,
and elbow with vanes, and a trunk duct teeing into
a branch duct with discharge diffuses. The transition
piece must not have angles totaling more than
30° or severe reduction in airflow performance can
result. Do not connect the full duct size to the unit. Use a
transition piece sized according to the discharge collar
on the unit to get to the full duct size. With metal duct
material, the sides of only the elbow and entire branch
duct should be internally lined with acoustic fibrous
insulation for sound attenuation. Glass fiber duct board
material is more absorbing and may permit omission of
the canvas connector.
The ductwork should be laid out so that there is no
line of sight between the unit discharge and
the distribution diffusers.
Do not use sheet metal screws directly into the unit
cabinet for connection of supply or return air ductwork,
especially return ductwork which can hit the drain pan
or the air coil.
Outside air may be required for ventilation. The
temperature of the ventilation air must be controlled so
that the mixture of outside air and return air entering
the
unit is within application limits. It is typical to close off
the ventilation air system during unoccupied periods
(i.e. night setback). The ventilation air system is typically a separate
building subsystem with distribution ductwork. Simple
introduction of the outside air into each return air
plenum chamber reasonably close to the unit air inlet is
recommended. Do not duct outside air directly to the
unit inlet. Provide sufficient distance for the thorough
mixing of outside and return air.
.
Ventilation Air