Setup & Operation; Basic Multi Boiler System Operation - HydroTherm HeatNet KN -6 User Information

SETUP & OPERATION
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 evenly distributed amongst all of the boilers. (See: Figure
35, Typical Single Boiler System, page 55).
Figure 2 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, page 61. 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 to 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 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 expired to zero, the process is repeated until the header
water temperature enters the heating band.
When a boiler receives a command to fire:
1. The system pump relay is enabled and the H-Net
control displays 'Flow Wait' until the flow-switch closes
between J11A, 1 & 2 within the programmed time
(10seconds).
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 'Damp: Wait' until the
damper end switch closes.
4. Relay K6 is enabled energizing the local pump (if
used). The H-Net control commences its 'Flow-Wait'
timer (adjustable 10–240 sec.). The flow switch contact
is checked on terminals J11B, 5 &6.
5. With all the interlocks closed, the boiler start relay K1
is enabled and energizes terminal 6 on the ignition
control. This signal is present on J5 Boiler Start
Operator.
6. The ignition control begins its cycle and provides an
output signal from terminal 4 to the H-Net control J5
Blower. The H-Net control responds and provides an
output signal to the VFD which sets the blower to the
programmed pre-purge speed. If an Ametek blower is
used, a soft start speed is applied before the pre-purge
speed.
7. After air-flow is established the ignition control waits
for the air switch to close. When the air switch closes it
provides an input to terminal 7 and pre-purge timing
commences. The H-Net display indicates 'Pre Purge'.
8. When purge is complete the ignition control energizes
the pilot gas valve from terminal 8, and the spark
generator from terminal 10, beginning a 10-second Pilot
Flame Establishing Period (PFEP). The H-Net control
responds to J5 Pilot Valve and provides an output
signal to the VFD which sets the blower to the
programmed ignition speed. The H-Net display
indicates 'Pilot'.
9. At the end of the PFEP the spark generator is de-
energized. If the pilot flame is detected, by the UV
scanner, the ignition control energizes the main gas
HeatNet Control V3 2.x
Page 10