JBE(X) Manual
Section C - Installation
and into the fan. In cases of heavy condensation, a
condensate drip leg may be required on the bottom of
the housing, to remove condensate.
e.
Determine the duct size, as indicated. Remember that
changing the fitting type and number of elbows can
have a large impact on the pressure drop. If the
pressure drop is too high, the unit will not make the
required NOx or input due to the increased pressure
drop. The burner capacity is reduced about 6% for
each 1” of pressure drop.
f.
Determine the location of the FGR shutoff valve
(linkage systems only). It can be mounted in either
the vertical or horizontal run, but it must be near the
top of a vertical run to reduce the potential for
condensation collection. If the valve is mounted in
a horizontal run, the valve shaft must be horizontal
(so condensation does not collect in the bearing) and
the actuator motor must be on top of the valve (with
insulation between the line and drive motor). Also,
there must be a condensation drip leg in the horizontal
run, before the shutoff valve, to remove condensation.
g.
Determine if pipe reducers are needed for the
connection to the FGR control valve and the FGR
shutoff valve.
h.
The duct must be properly supported, to handle its
own weight and to control the thermal expansion and
contraction. The supports may need to be anchored
to provide this stability in the FGR duct.
CAUTION
UNCONTROLLED CONDENSATION CAN CAUSE
PREMATURE FAILURE OF THE CONTROL VALVES,
FAN AND MOTOR. ADEQUATE MEANS MUST BE
PROVIDED TO REMOVE CONDENSATION FROM THE
SYSTEM. COLD STARTUP WILL GENERATE SIGNIFI-
CANT AMOUNTS OF CONDENSATION.
i.
The FGR duct is normally made from schedule 40
pipe because it is obtainable and inexpensive.
Schedule 20 pipe can also be used.
j.
The duct components must be seal welded, flanged
or screwed together to provide an airtight duct. Air
leakage into the duct will prevent the system from
working properly. It’s sufficient to inspect the welds
for a proper seal. They don’t need to be leak tested.
10. Draft and Stacks
Stacks and breechings must be designed to maintain
a relatively constant draft at the boiler outlet without
large variations. The draft at the boiler outlet should
be maintained /- 0.1” wc. More important than
the actual draft is the variation in draft at any given
firing rate. For example, a tall stack or multiple units
in a single stack may have different draft conditions
depending on the outside temperature and the number
of units running. The draft variation at any given firing
rate should be controlled to /- 0.05” wc.
The stack should be designed to avoid wind influences
from adjacent structures as well as preventing the flue
products from entering inlet ducts, windows or other
occupied areas. It should be of sufficient height to ex-
tend above the roof of the building or adjoining build-
ings to avoid down drafts in the stack or the possibility
of carrying combustion gases to undesirable locations.
Local codes should be checked for criteria on heights
and exit velocities. The breeching should be designed
to be as straight and short as practical, to minimize
pressure fluctuations. Smooth bends, gradual transi-
tions, low velocities and tight construction are all im-
portant. Round breechings are preferred to square or
rectangular ducts because they are more efficient and
less likely to generate noise on the flat side due to
10 HP
NAMEPLATE
O
C
45°
FGR Shutoff Valve
(Linkage Units Only)
Drain Valve
FGR Duct (Typical)
Drain Line
Condensate
Trap
Drain Valve (Manual Ball
Valve, Stainless Steel)
Stack
FGR Control Valve
Alternate Construction
Using "Tee"
Stack
Figure C-13
FGR Duct Installation
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