A.O. Smith 2000 Instruction manual - page 24
24
8. PRIMARY SYSTEM CONTROL
All VF boiler installations require a “Primary System Control” that
senses and reacts to water temperature inside the storage tank
on domestic water applications or in the return line on primary/
secondary hydronic heating systems. The Primary System Control
will activate and deactivate boiler heating cycles based on its
setpoint and current system water temperature. There are three
suitablemethodstoconfigureaPrimarySystemControl.Oneof
these three methods MUST BE used.
1. The Primary System Control can be the boiler’s control system
working with the factory supplied Remote Temperature
Probe or the optional Quad Thermistor Probe installed inside
the storage tank on domestic water applications or in the
return line on primary/secondary hydronic heating systems.
See the Field Wiring and the Remote Temperature Probe
Installation sections in this manual. This application ensures
theboiler’sabilitytofullymodulateitsfiringrate.
2. Alternatively, the iCOMM™ system hardware working with
an onsite BACnet compliant BMS (Building Management
System) can be used as a Primary System Control. This
application ensures the boiler’s ability to fully modulate its
firingrateandallowsBACnetcompliantcontrolstoutilize
outdoor temperature reset schedules to maximize energy
savings on hydronic heating applications during medium
and low load conditions. iCOMM™ system hardware is
purchased separately from the manufacturer. For more
information call 888 928-3702.
3. ThePrimarySystemControlmayalsobeafieldsupplied
external control such as a storage tank thermostat or boiler
sequencing panel. Field supplied external controls must
have a set of “dry” (no voltage or load) control contacts to
use with the boiler’s Enable/Disable circuit to activate and
deactivate boiler operation, see the Field Wiring section in
this manual for wiring instructions. Field supplied Primary
System Controls must be able to sense water temperature
inside the storage tank on domestic water applications
or in the return loop on primary/secondary hydronic
heating systems. If the external control has no provision
(temperature sensor) to sense system temperature in this
way it must not be used as a Primary System Control.
NOTE:Whenafieldsuppliedexternalcontrolisusedas
the Primary System Control it activates and deactivates
boiler operation based on the temperature it senses in the
system.Itcannotcontroltheboiler’sfiringrate.Theboiler
willnotbeabletofullymodulateitsfiringratewhenusing
this type of Primary System Control.
When using an external supervisory control as the Primary
System Control the Operating Setpoint of boiler control
system must be set at least 5° higher than the system
setpointofthefieldsuppliedPrimarySystemControl.This
is done to ensure the boiler’s setpoint does not deactivate
the current heating cycle before the external control’s setting
hasbeensatisfied.Thisalsopreventstheboilerfromshort
cycling. See the Operating Setpoint Adjustment Procedure
in this manual for instructions on how to change the boiler’s
Operating Setpoint.
REMOTE TEMPERATURE PROBE INSTALLATION
All VF boilers are supplied from the factory with a Remote
Temperature Probe which is suitable for all single boiler
applications. When connecting up to 4 boilers to a single storage
tank or one Primary/Secondary Hydronic Heating system the
optional Quad Thermistor Probe should be used. Call the toll free
support phone number on the back of this manual to order the
Quad Thermistor Probe.
On domestic hot water applications the Remote Temperature
Probe or the optional Quad Thermistor Probe must be installed in
the designated temperature control opening on the storage tank,
typically a 3/4 inch NPT opening in the lower portion of the tank.
On hydronic heating applications the probe being used must be
installed in the return line of the primary hydronic heating loop
before(upstream)thefirstboiler.Seethepipingdiagramsinthis
manualforprobelocation.AfieldsuppliedTeefittingwitha3/4
inch NPT branch is installed in the return line for this purpose.
Once the probe has been installed in the system, see the Field
Wiring section of this manual for wiring instructions.
Whentheprobehasbeeninstalledandthefieldwiringiscomplete
the probe must be designated as the “Controlling Probe.” To do this
turn off power to the boiler and locate the SW1 dipswitches on the
boiler control system’s MCB circuit board. SW1 dipswitch #4 must
besettothe“On”positiontoconfiguretheRemoteTemperature
Probe or the optional Quad Thermistor Probe as the Controlling
Probe. The SW1 dipswitch #4 is set to “Off” from the factory so
this reconfiguration must be performed on all installations. See
the MCB - Ten Position Dipswitch SW1 section of this manual for
instructions on how to change dipswitch settings. When power to
the boiler is turned back on the boiler’s control system will now
monitor the remote probe that was installed and use temperature
data from the probe to activate and deactivate heating cycles and
tomodulatethefiringrateoftheboiler.
FIELD SUPPLIED EXTERNAL CONTROL INSTALLATION
On domestic hot water applications the temperature sensor for
the field supplied Primary System Control must be installed in
the designated temperature control opening on the storage tank,
typically a 3/4 inch NPT opening in the lower portion of the tank.
On hydronic heating applications the temperature sensor must
be installed in the return line of the primary hydronic heating loop
before(upstream)thefirstboiler.Seethepipingdiagramsinthis
manualforlocation.AfieldsuppliedTeefittingwitha3/4inchNPT
branch is installed in the return line for this purpose.
See the Field Wiring section of this manual and the instructions
that came with the field supplied control to connect the
external control to the boiler’s Enable/Disable circuit.
INTERNAL CONTAMINANTS
The hydronic system must be internally cleaned and flushed
after a new or replacement boiler has been installed, to
remove contaminants that may have accumulated during
installation. This is extremely important when a replacement
boiler is installed into an existing system where Stop Leak
or other boiler additives have been used.
Failure to clean and flush the system can produce acid
concentrations that become corrosive, and leads to heat
exchanger failure.
All hot water heating systems should be completely flushed
with a grease removing solution to assure trouble-free opera-
tion. Pipe joint compounds, soldering paste, grease on tubing
and pipe all tend to contaminate a system
Failure to flush contaminants from a system can cause solids
to form on the inside of boiler exchangers, create excessive
blockage of water circulation, deterioration of the pumps seal
and impellers.
HOT WATER SUPPLY BOILER SYSTEM-
GENERAL WATER LINE CONNECTIONS
This section provides detailed installation diagrams for a typical
method of application for the unit.
Piping diagrams will serve to provide the installer with a reference
for the materials and methods of piping necessary for installation.