SETUP & OPERATION
HeatNet Control REV 1.38-1
Page 10
As boilers are added to the system the
ADVANCED
SETUP:ADAPTIVE 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: Smith HeatNet
Control: Master
).
If all boilers are firing, the modulation rate is allowed 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.
Once the header water temperature is in the band, only
the modulation rate is used to achieve the target setpoint.
The system will then maintain 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 while trying to
keep the temperature within the heating band. If the
system is now delivering too many heating BTUs, the
water temperature will cross the top of the heating band.
When the header water temperature first exits the top of
the heating band, the runtimes of the boilers are again
checked for the one with the most runtime. The selected
boiler will then turn off immediately and a shed boiler
delay timer will be loaded with the SHED BOILER
delay time. This time will need to expire before the next
boiler will stop, but only if the header water temperature
remains above the heating band. This timer is used to
allow the header water temperature to settle 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
immediate large discontinuous loss of BTUs.
This cycle will continue until the call for heat is removed
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.
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.
Mixed Boiler System Operation
Starting Boilers:
When a boiler is to be fired (water temp is below the heating
band), the Master checks the HeatNet boilers it has
available. The Master boiler then looks at which boilers are
returning priority firing status (set on a boiler in:
(ADVANCED SETUP:SYSTEM:BOILER
TYPE:PRIORITY :
1
). If the Start condition for the Priority
1set is met (ADVANCED SETUP:FIRING MODE:
MODE: MIXED:SET
FIRST
(
example
), the Master or
Member boiler that is configured as PRIORITY 1, with the
lowest runtime, will be fired
FIRST
(
example
).
As long as the start condition for Priority 1 is met, all
boilers in the PRIORITY 1 set will fire based on runtime.
Once all boilers in the PRIORITY 1 set have fired, the
PRIORITY 2 set of boilers will fire based on runtime.
If the Start condition changes and/or is not met (such as
with: OA T or RET temp), the PRIORITY 2 set of boilers
will fire first/next based on runtime. This has the effect of
flipping the priority of the sets.
Stopping Boilers:
When a boiler is to be stopped (water temp is above the
heating band), the Master checks the HeatNet boilers it has
available. The Master boiler then looks at which boilers are
returning priority firing status (set on a boiler in:
(ADVANCED SETUP:FIRING MODE: MODE:
MIXED:SET
LAST
(
example
) If the Stop condition for
Priority 1 is met, the Master or Member boiler that is
configured as PRIORITY 1 with the highest runtime will be
stopped
LAST
(
example
). As long as the stop condition and
SHED DELAY time are met, all remaining PRIORITY 1 set
of boilers will stop based on runtime. If the Stop condition
changes and/or is not met (such as with: OA T or RET
temp), the PRIORITY 2 set of boilers will stop first/next
based on their highest runtime.
A boiler’s firing priority can be designated as such in:
“ADVANCED SETUP:SYSTEM:BOILER TYPE:FIRING
PRIORITY : 1” menu on each boiler. A priority of ‘1’ is the
highest priority, a ‘2 the lowest (default is always 2).