YORK INTERNATIONAL
18
FIG. 16 –
DUCT PENETRATION OF ROOF
FIG. 17 –
ROOF TO DUCT INSTALLATION -
HORIZONTAL DISCHARGE
When a unit is used with a ceiling plenum return air
system, sound may be transmitted from the unit through
the ceiling to the conditioned space. For such applica-
tions, there should be a sound absorption chamber in-
stalled on the unit return air inlet. Various reference
sources are available regarding acoustic design.
On units with return fans it is espe-
cially important to consider the effects
of sound transmission into the condi-
tioned space.
FRONT DISCHARGE UNIT INSTALLATION
1. Roof penetrations by ducts should utilize
counterflashed curbs. (Typical arrangements are
shown in Figure 16.)
2. All penetrations into ducts should be sealed water-
tight. Attachment of supports should use a mini-
mum number of duct penetrations.
3. Duct systems should not be pressurized without suf-
ficient time for curing of sealant systems. Follow
sealant manufacturers recommendations for appli-
cation of the sealant.
4. Adequate clearances between ducts and roof pen-
etration openings should be provided.
5. Ducts should be supported to avoid transfer of duct
weight across flexible connections. (See Figure 17)
6. Horizontal ducts should be pitched and provided with
drainage outlets as illustrated (by the system de-
signer).
7. Ducts should be installed at a height sufficient to
install roofing and flashing.
PIPING
1. Whenever possible, piping should be brought down
through the unit within the pipe chase. (See Figures
18 and 19)
2. Where piping is insulated, insulation should not be
installed until after the flashing has been completed.
COIL PIPING
Consult the job specifications and submittal drawings for
specific piping requirements, coil connection sizes and
location. The unit should be level to assure proper vent-
ing and draining of coils. The piping arrangements must
provide for a balanced flow in multiple coil installations.
(See Figure 20 showing factory coil connections.)
The coils will meet performance ratings only if the air
flow is uniform over the face of the coil. High air ve-
locity spots on the coil may cause the carry-over of
moisture from the coil. Low air velocity areas of the
coil will not deliver the published ratings. The duct con-
nections must be designed to provide for uniform flow
of air across the face of the coil. The entering duct
must provide a smooth transition from any high velocity
effects. Stratifications of return air, especially where
below freezing outside air enters, must be avoided to
prevent coil freeze-up.
Installation
LD06494
LD06337
