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Figure 10. Single or Multiple Boiler Installation Diagram
The circuits should be spaced on the header at a minimum of
3" (7.6 cm) center to center. Install a balancing cock in each return
line.
Manifold headers are recommended for split systems with or
without zone valves and also those installations with zone
circulators. If the system is to be split at remote points, good practice
requires special attention be given to main pipe sizing to allow
balancing of water flow.
COOLING PIPING
When the boiler is used in conjunction with a refrigeration system
it must be installed so that the chilled medium is piped in parallel
with the boiler. Appropriate valves, manual or motorized, must be
provided to prevent the chilled medium from entering the boiler.
Water temperature in the heating system must be reduced to less
than 100°F before cooling system is started, or damage to the
chiller unit may occur.
If the boiler is connected to chilled water piping or heating coils
exposed to refrigerated air, the boiler piping system must be
equipped with flow control valves or other automatic means to
prevent gravity circulation through the boiler during the cooling cycle.
Primary/secondary pumping of both the chiller(s) and the boiler(s)
is an excellent winter-summer change-over method, because
cooling flow rates are much more than heating flow rates. In this
way each system (heating or cooling) is circulated independently.
SPACE HEATING APPLICATIONS
Controlling of these systems is decided mainly by the type of
building system controlling that is desired. A single boiler
installation might be controlled directly from space temperature
thermostat(s). Multiple boiler installations are more effective when
the boilers are sequenced in and out of operation by some form of
main water temperature controller. With one or two boilers, individual
control settings at progressive temperature may be used. For more
than two boilers, electronic sequencing controlling is
recommended.
Individual controls, or the separate stages of a step controller,
should fire a boiler and also start the boiler loop circulator whenever
that boiler is fired. Some large installations may require the firing
of more than one boiler per stage.
The system or primary circulator may or may not be controlled by
the boiler sequencer. When this pump is operated through the first
switch of any type of step controller, care should be taken to
determine if a motor starter is needed due to insufficient switch
capacity.
If the primary pump is controlled by a manual switch or any other
controllers, the electric current supply to the boiler group should be
through the primary pump controller. The fast response of
A.O. Smith boilers eliminates any need to maintain boiler
temperature when the system is satisfied. Wiring should always
prevent firing of boiler(s) when there is no water flow in the
mains.
Installation diagrams show safety flow switches in the outlet piping
from each boiler as good protection against any boiler being fired
when the boiler loop circulator is not in operation. These safety flow
switches will also provide some protection if there is a loss of water.
Multiple boiler installations are especially adapted to the use of
outdoor reset for main water temperatures. This feature is not