SETUP & OPERATION
Page 12
SETUP & OPERATION
Basic Multi Boiler System Operation
For boiler system setup/installations
please refer to the 2008 ASHRAE Handbook, CH12 or later
revision.
A basic multi boiler system typically uses boilers of the
same size and type. With HeatNet, this includes (1) Master
and (1-15) Member boilers. The boilers are connected
together using an H-Net communications cable effectively
creating (1) boiler. This allows the system heating BTUs to
be evenly distributed amongst all of the boilers.
The Version 1.6 HeatNet board requires Minibus
connections for FlexCore boilers with more than (1) heat
exchanger. The Minibus requires a serial data cable between
each HeatNet Control board. The first and last Heat
Exchanger must have the minibus terminated for the bus to
work properly. S1 would be placed in the ON position as
indicated below for the front and rear heat exchangers. The
jumper, JS1 must always be in the position indicated
(closest to S1). It is used for testing.
Basic multiple boiler system
A basic multi boiler system can be configured using the
boiler menus to create custom systems/features. These
features are best described in the section: Default Settings
& Menu Item Description. Along with these menu items
are hardware support for many auxiliary functions.
Once the system has been properly setup (all default menu
values used and H-Net addresses assigned), the system is
enabled by placing the REMOTE/LOCAL switch to the
LOCAL position on the Master boiler. All Member boilers
must have their respective switches in the REMOTE
position. When the Master boiler’s Heat Demand input
(LOCAL switch) closes, the system becomes operational
and will fire as many boilers as it needs to maintain the
header water temperature’s setpoint. See the DHW section
to fire using two setpoints.
When a boiler is to be fired in a multi boiler system (header
water temperature is below the heating band), the Master
checks the HeatNet boilers it has available. Then the Master
checks if a Lead Boiler is to be used (LEAD BOILER > 0).
The Master boiler then looks at which type of firing rotation
it has selected: LOFO, FOFO, TRUE (runtime), or MIXED.
In our example we will use the TRUE (runtime) rotation
since it is the default.
The Master now checks all of the runtimes to determine
which boiler has the least runtime based on the MIN
RUNTIME setting in SETTINGS: FIRING MODE: The
MIN RUNTIME setting is the minimum runtime interval in
hours that is used to compare boiler to boiler runtimes.
Once the boiler designated to fire has been determined, the
Master sends the command over the H-Net cable to fire that
boiler and resets the ADD BOILER delay timer to prepare
for the next boiler to fire. If the header water temperature is
still below the heating band and the ADD BOILER delay
timer has expired to zero, the process is repeated until the
header water temperature enters the heating band.
When a boiler receives a command to fire:
NOTE: Runtime messages are displayed in the lower left
corner of the Home Screen. See Section Messages for
descriptions.
1. The system pump relay is enabled and the H-Net
control displays “Waiting for Flow” until the flow-
switch closes between J11A, 1 & 2 within the
programmed time (10 seconds default).
2. All elements in the interlock string, terminated between
J11A and J11B, must be closed before the sequence is
allowed to continue.
3. If all interlocks are closed, relay K5 is enabled to
command the combustion-air damper open (if used).
The H-Net control displays “Waiting for Damper to
Open” until the damper end switch closes.
4. Relay K6 is enabled energizing the local pump (if
used). The H-Net control commences its Waiting for
1 to 16 Boilers
Member BoilersMaster
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