Owner's Manual
32
3.2.3 Primary-secondary pumping is preferred as it does
accomplish the desired fuel economy. To get the
same economy from parallel pumping it is necessary
to install some mechanism which will prevent ow
through unred modules as well as to install separate
supply and return headers. Thus, the total installed
cost of primary-secondary pumping may not be more
than that of a properly controlled parallel pumping
system.
3.2.4 If after careful consideration, the system designer
decides to use parallel pumping, a system using
reverse return headers as shown in Figure 3-1
is recommended. Direct return headers are not
recommended because direct returns are inherently
unbalanced and may prevent some modules from
delivering their rated capacities.
3.2.5 Optional fabricated manifolds are available as
a convenience to the installer and are highly
recommended with four or more modules.
3.2.5.1 Factory fabricated manifolds are lightweight and
quite forgiving of minor piping misalignments
common to multiple boiler installations. Each end
of the 4” manifold is ready for connection to another
manifold section or to the eld piping by means
of: 1. optional self-restrained pipe couplings,
or 2. eld roll-grooving for use of groove style
couplings. One lateral connection on each manifold
is threaded and intended to be made-up rst to
positively locate the manifold during its installation.
The other lateral connections on each manifold are
longer also threaded for those installations where
threaded ttings, such as unions, are desired, but it
is recommended that these longer threaded laterals
be cut off to yield plain ends for applying the same
style couplings as on the 4” ends.
3.2.5.2 The lateral connections on the factory fabricated
manifolds for use with 805H, 806H, and 807HE
modules are 1½” schedule 40, equally spaced on
28½” centers. The lateral connections on the factory
fabricated manifolds for use with 808HE, 809HE,
and 810HE modules are 2” schedule 40, equally
spaced on 40” centers. If an 807HE and an 808HE
module are to be connected to a common manifold,
use the longer manifold with 40” spacing.
3.2.5.3 Manifolds are available to serve two or three
modules. Two-module manifolds have two return
and two supply lateral connections, three-module
manifolds have three of each.
3.2.5.4 The manifolds are adaptable to parallel pumping
applications by capping half of the lateral
connections and using two manifolds: one for
supply and one for return. Refer to Figure 3-1.
3.2.5.5 A fundamental advantage of primary-secondary
pumping over parallel pumping is that water
temperature rise and ow rate thru each module
in a primary-secondary system is independent of
the system temperature drop and ow rate. Hence,
module piping to and from the manifold and
the module circulators on a primary-secondary
application may be based on a higher temperature
rise thru the module, say 30° or 40°F, and downsized
from the lateral connections. The module piping,
valves, and circulator for primary-secondary
pumping may be sized from the data in Figure 3-4.
3.2.5.6 For parallel pumping applications module piping
should equal the lateral connection sizes. Refer to
Figure 3-4 for module ow rates and pressure drop.
3.2.5.7 The maximum ow capacity of the factory fabricated
manifold is 265.GPM. If the system is based on a
20°F ∆T, these manifolds could serve modules with
a total input of 3400.MBH. If the system is based
on ad 30°F ∆T, these manifolds could serve modules
with a total input of up to 5100.MBH.
3.2.5.8 If the optional ex couplings shown in Figures 3-1
through 3-3 are to be used, they should be installed
according to the instructions in section 3.16.
3.2.5.9 If groove style couplings are to be used, they should
be installed according to the instructions in section
3.17.
3.2.6 On fewer than four modules, the designer may elect
to use commercial schedule 40 pipe and ttings of
a smaller size than the 4” pipe size of the fabricated
manifolds. Refer to 3.4.1 for the procedure used to
size a eld fabricated manifold. It should be noted
that in the case of primary-secondary pumping the
return line to each module should not be down stream
of the supply line from that same module to avoid
short circuiting of heated water within that module.
3.2.7 On a scaled drawing of the boiler room, layout the
selected water manifolds and mains.
3.3 STOP VALVES—Another prime reason for using
modular boilers is that of servicing without shutting
down the entire system. Any individual module
can be shut down for cleaning or repairs without
interrupting the operation of the remaining modules.
This is true of electrical components and the gas
components because most codes require a service shut
off at each module. A mistake is often made by not
installing water stop valves at the headers for each
module. By installing stop valves at the headers for
each module it becomes easy to perform repairs to
the water side of the module, such as leaky ttings,
control wells, and pumps. Without stop valves
each such service call results in the aggravation of a
system shut down. In addition, it takes time for the
serviceman to drain before the repairs and then rell
and vent the system after the repairs. That additional
service time may cost the owner more over the life
of the system than the cost of the stop valves at the
time of installation. Finally, the use of water side
stop valves on each module is required by some codes
in order to exclude the header and inter-connecting
water piping from consideration as an integral part of
a boiler. Stop valves are recommended as shown in
Figures 3-1 through 3-3.