SETUP & OPERATION
HeatNet Control V3 3.x
Page 17
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 airflow is established the ignition control waits
for the air switch to close. When the air switch closes it
provides an input to terminal 7 of the Honeywell FSM
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 blower which sets the blower speed 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
valve from terminal 9 to
J5 Main Valve
. The H-Net
display indicates “Running 0%” (0% indicates PID
modulation signal is not being calculated yet).
10.
If main-flame is detected the H-Net control holds the
burner at the low-fire rate for the
MODULATION
DELAY
time period. After this timer expires, the PID
allows the boiler to modulate and places the boiler into
the running state.
As boilers are added to the system settings in the
SETTINGS: ADAPTIVE MODULATION MOD: DROP DOWN
menu determines when the modulation rate drops down to
compensate for the newly added BTUs. For the drop down
to be active, one boiler needs to be running when a new
boiler is added (see:
Introduction: The KN-SERIES H-Net
Control: MASTER
).
If all boilers are firing, the modulation rate is released to go
to 100%. If all boilers are not firing, the modulation is
limited to the MOD-MAX clamp value. The MOD-MAX
clamp is used to keep the boilers running as efficiently as
possible. The following
Mixed Boiler System Operation:
Selecting Mixed Boilers
section outlines this with examples.
If the boiler is running as a stand-alone
boiler or is direct modulated (including the
AA input), the MOD-MAX clamp will also be
in effect for the ADD BOILER DELAY time.
This is to minimize thermal shock to the boiler.
Once the header water temperature is in the heating band,
only the modulation rate is used to achieve the target
setpoint. The system will maintain the setpoint until the load
demand increases or decreases.
As the load decreases, the header water temperature will
start approaching the top of the band. The PID now lowers
the modulation rate to the boilers, attempting to keep the
temperature within the heating band. If the system is
delivering too many BTUs, the water temperature will cross
the top of the heating band.
When the header water temperature first exceeds the top of
the heating band, the boilers are again checked for the one
with the most runtime. The selected boiler will turn off
immediately and a “
Shed Boiler Delay”
timer will be
loaded with the delay time. This time will need to expire
before the next boiler will be stopped, but only if the header
water temperature remains above the heating band. This
timer is used to allow the header water temperature to return
back into the band when a boiler is stopped. When a boiler
is stopped there is a fixed rate of BTUs (Min Fire) that will
be removed (PID discontinuity to modulate from Min Fire
to 0 BTUs on a boiler). The timer allows for this loss of
BTUs.
This cycle will continue until the call for heat is satisfied or
the Warm Weather Shutdown feature is enabled.
Mixed Boiler Types Using
Priority Sets
Using the
Basic Multi Boiler System Operation
, a
MIXED
BOILER PRIORITY
method may be added to control
condensing, non-condensing, base load, or other boiler sets
in a system
together. These sets compose a system which
provides for optimal performance and economy. Having
dedicated sets of boilers gives the system engineer a tool to
create many different boiler systems.
A boiler set can be constructed by simply setting the
FIRING
PRIORITY
on each boiler (to be in a set) at the
same Priority. Setting all (example) condensing boilers to
the highest Priority of 1, and then setting all (example) non-
condensing boilers to a Priority of 2, will create (2) sets of
boilers, one condensing and the other non-condensing. Once
this is done, the Priority 1 set of condensing boilers will
have a firing order that has a higher Priority and is
independent of the other non-condensing set with the lower
Priority. The boiler set with the highest Priority can then be
fired based on a conditional settings menu. The lower
Priority set will follow.