SETUP & OPERATION
HeatNet Control REV 1.38-1
Page 9
SETUP & OPERATION
Basic Multi Boiler System Operation
For boiler system setup/installations please
refer to 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 distributed amongst all of the boilers. (See:
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Figure 2
Basic multiple boiler system
Master
Members
1 to 15 boilers total
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,
page 46
. 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 HeatNet 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. Once the Master boiler’s Heat Demand input
(LOCAL switch) closes, the system is operational and will
fire as many boilers as it needs to maintain the header water
temperature’s setpoint.
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 ADVANCED SETUP: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 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 counted down to 0, the process is repeated until the
header water temperature enters the heating band.
When a boiler receives a command to fire it:
1.
Enables the System Pump Relay and waits for the
System Flow Prove switch to make in the interlock
string (J5B.1).
2.
Next, the interlock string is checked for any other
tripped interlocks (J5A & J5B). Also, the High Limit,
Ignition Control, Gas Valve Prove (Optional), and any
hardware faults (sensors, etc…) are checked before
continuing.
3.
If all interlocks are good, and if the combustion air
damper is used, the K5 combustion air damper relay is
enabled. The damper prove switch is then monitored for
closure.
4.
The local pump relay K6 is now energized and the
proof of flow is monitored for closure on J5B.7.
5.
With all interlocks good, the boiler start relay K1
energizes and provides a signal to terminal 6 of the
ignition control.
6.
The ignition control then begins an ignition cycle by
first energizing its blower relay. The H-Net control then
sets the blower VFD to the Pre-purge speed.
7.
The ignition control then waits for the air switch to
close by monitoring its terminal 7.
8.
Once the pre-purge time expires on the ignition control,
it closes its pilot valve relay causing the H-Net control
to adjust the blower to the ignition speed and attempt to
light the pilot.
9.
If the pilot is successful, the ignition control energizes
its main gas valve relay and starts its trial for main
flame (UV scanner).
10.
Once the main flame is proven, the H-Net control holds
the fire rate at low fire for the MODULATION
DELAY time period. After this time expires, the PID
modulation is then allowed to modulate the boiler and
places the boiler in the running state.
