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Large systems with multiple boilers should include main water
temperature controls (with or without outdoor reset) to sequence the
boiler on and off, in relation to the load on the system.
24 VAC System Controller (Optional)
GB models require a field supplied 24VAC operating control to be
installed in the system such as: loop thermostat, indoor/outdoor reset
control, sequencing panel, or energy management system. The
connection for such devices is located in the 24 VAC junction box at
the rear of the unit. A 24 VAC thermostat/aquastat can only be used as
an "On/Off" switch for the unit. The actual controlling of the staging will
be through either the inlet or tank probe.
INTERNAL CONTAMINANTS
The system must be internally cleaned and flushed after a new or
replacement unit has been installed to remove contaminants that
may have accumulated during installation. This is doubly important
when a replacement unit is installed into an existing system where
Stop Leak or other boiler additives have been used.
All systems should be completely flushed with a grease removing
solution to assure trouble-free operation. Pipe joint compounds, soldering
paste, grease on tubing and pipe all tend to contaminate a system.
Failure to clean and flush the system can cause solids to form on
the inside of the heat exchanger, can produce acid concentrations
that become corrosive, can allow excessive amounts of air or other
gases to form which could block circulation, foul system
accessories and damage circulator seals and impellers.
It is recommended that after installation, the boiler and system
when filled should include the proper percentage of cleaning solution
This bypass may also be used with multiple boilers manifolded for
reverse-return flow. The system bypass would be installed from boiler
outlet to suction side of pump.
The boiler piping system of a hot water heating boiler connected to
heating coils located in air handling units where they may be
exposed to circulating refrigerated air, must be equipped with flow
control valves or other automatic means to prevent gravity circulation
of the boiler water during the cooling cycle. It is highly recommended
that the piping be insulated.
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
start the boiler loop circulator and fire the boiler. 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.
Multiple boiler installations are especially adapted to the use of
outdoor reset for main water temperatures. This feature is not
mandatory but offers smooth, efficient operation of a modern
system.
Normal use of flow control valves is required to prevent cross
circulation of zones as with any multiple pump system.
Figure 10. Single or Multiple Boiler Installation Diagram