Rapid 4044, Installation, Operation & Service Manual

Page: 77 / 162

SECTION 17: D
UCT
C
ONSIDERATIONS
69 of 154
SECTION 17: DUCT CONSIDERATIONS
The air handler has been designed to operate at the
specific air
v ol u me and external static press u re that
w as originally specified. Static press u re is increased
by any additional components that are added to the
air handler (i.e. inlet hood, filter section, dampers,
d
u ct w ork, discharge heads, etc) Additional static
press u re beyond original intention (or time of order)
w ill affect the performance of the air handler and
red u ce the air v ol u me that can be deli v ered.
Proper engineering methods need to be employed
w hen calc u lating d u ct and component static press u re
(i.e. 2009 ASHRAE Handbook - F u ndamentals,
Chapter 21).
The system d
u ct w ork m u st comply w ith Sheet Metal
and Air Conditioning Contractors Nationals
Association (SMACNA) or any other recognized
standards.
As a general r
u le, all d u cting sho u ld ha v e a straight
r u n of at least 3 d u ct diameters immediately before
and after the air handlers mechanical accessories.
No d
u ct fittings, elbo w s or transitions w ith restrictions
can be placed w ithin 3 d u ct diameters.
D u ct diameter for ro u nd d u cts (in inches):
Dh = d
Dh:diameter
d:ro
u nd d u ct inside diameter
D u ct diameter for rectang u lar d u cts (in inches):
Dh = (2*H*W)/(H+W)
Dh:diameter
H:rectang
u lar d u ct inside height
W:rectang u lar d u ct inside w idth
The air handler is not designed to s u pport the w eight
of d u ct w ork. D u ct w ork m u st be constr u cted in a
fashion that is self-s u pporting. D u ct w ork sho u ld be
straight, elbo w s sho u ld be minimal and any
transitions sho u ld be grad u al.
Depending on the options ordered w ith the air
handler, flanges (either external or internal) may be
pro
v ided to facilitate connection of d u ct w ork. In
cases w here flanges are not pro v ided, flat s u rfaces
on the exterior skin of the air handler are pro v ided to
facilitate connection of d u ct w ork.
Neither the flanges nor exterior skin of the air handler
are capable of s
u pporting the load of the d u ct w ork.
D u ct w ork s u pport m u st come from the str u ct u re itself
that the air handler is ser v icing. On horizontal r u ns, it
is recommended that d u ct w ork be s u pported e v ery 6
ft (1.8 m) for d u ct w ork that has a cross section of 10 ft
(3 m) or less and e v ery 4 ft (1.2 m) for d u ct w ork
w hich has a cross section of greater than 10 ft (3 m).
On v ertical r u ns, it is recommended that d u ct w ork be
s u pported e v ery 10 ft (3.0 m). On both cases,
s u pporting members sho u ld be sized to carry the
w eight load.
17.1 Inlet Air Duct
Inlet d u ct w ork height and w idth m u st be no smaller
than the air handler inlet height and w idth and s u pply
only u ncontaminated air to the air handler. ( See
Page 10, Section 5 for ret u rn air dimensions).
17.2 Return Air Duct
Ret u rn air d u ct w ork height and w idth m u st be no
smaller than the air handler ret u rn air opening height
and w idth. ( See Page 10, Section 5 for ret u rn air
dimensions).
17.3 Supply Air Duct Work
S u pply air d u ct w ork sizes sho u ld be determined by
the application req u irements of the system. S u pply
air d u ct w ork m u st be smaller than s u pply air
opening. See Page 10, Section 5 for dimensions.
Cut/Pinch Hazard
Wear protective gear
during installation,
operation and
service.
Edges are sharp.
Falling Hazard
Use proper safety
equipment and prac-
tices to avoid falling.
WARNING
Failure to follow these instructions can result
in death, injury or property damage.