SETUP & OPERATION
HeatNet Control REV 1.38-1
Page 12
2.
The Outside Air Temperature is below an adjustable
setpoint determined by the system configuration. This
setpoint ensures that the larger non-condensing boilers
run during the coldest months when maximum heating
is required. Above this setpoint smaller condensing
boilers should be brought on first to run the system as
efficiently as possible.
3.
Maximum heating is required
START PRIORITY 1 SET SELECTIONS
(Always the lowest runtime first):
The
condensing boiler set
(Priority 1) has a
higher Priority to
fire
when one of these
conditions is met. Values are adjustable.
FIRST
:
The condensing boilers (Priority 1) are always
started FIRST
OA T > 15F
:
The condensing boilers (Priority 1) are
started when the OA temperature is greater than the Mixed
Boiler Outdoor Air Temperature setting.
RET < 140F
:
The condensing boilers (Priority 1) are
started when the Return water temperature is less than the
Mixed Boiler Return temperature setting (This may not
applicable in most configurations since the local return
temperature on the Master is used to provide a difference
temperature across the heat exchanger. However, the return
temperature sensor may be moved on the Master to provide
system return temp if the difference temp is not required).
STOP PRIORITY 1 SET SELECTIONS
(Always the highest runtime first):
The
condensing boiler set
(Priority 1) has a
higher Priority to
stop
when one of these
conditions are met. Values are adjustable.
LAST:
The condensing boilers (Priority 1) are always
stopped LAST.
OA T < 15F:
The condensing boilers (Priority 1) are
stopped first when the OA temperature is less than Mixed
Boiler Outdoor Air Temperature.
RET > 140F:
The condensing boilers (Priority 1) are
stopped first when the Return water temperature is greater
than the Mixed Boiler Return temperature. (This may not
applicable in most configurations since the local return
temperature on the Master is used to provide a difference
temperature across the heat exchanger. However, the return
temperature sensor may be moved on the Master to provide
system return temp if the difference temp is not required)
Start/Stop settings
Any combination of Start Conditions and Stop Conditions
can be used to optimize the mixing of condensing (Priority
1) and non-condensing boilers (Priority 2) for best
performance/economy.
The default settings for the start and stop conditions of the
condensing set are:
The default start setting always starts the condensing boilers
(Priority 1 example) first, except for the lead boiler setting.
The
lead boiler
will always start first if enabled, unless
there is a boiler already running (this includes a Member
boiler in LOCAL). The default stop condition setting always
stops the condensing boilers (Priority 1) last.
If prolonging the life of the heat exchanger(s) on non-
condensing boilers is very important, consider starting the
condensing boilers (KN series) when the return water
temperature is below 140F.
The return water temperature sensor would
need to be moved from the Master’s return
inlet to the system return. The
EXCHGR
DELTA
may need to be adjusted in
SETUP:AUX FUNCTIONS:HEAT
EXCHANGER
to prevent the Master from
going to ½ input when a high
DELTA T
is
reached.
This method would lead to the non-condensing boilers
carrying the load when the system temperature
stabilizes above 140F, since non-condensing boilers
will start first with the Return water temperature is >
140F. The condensing boilers can then be stopped first
when the RET water temperature is above the 140F.
Remember, any combination of the Start and Stop
conditions may be applied for best performance and
economy in the system.
Base load boilers can also be mixed in the same way as
condensing and non-condensing boilers. The base load
boiler(s) can be prioritized in one set (example, Priority
2) and non-base load boilers (Priority 1). The non-base
load boilers can then be set to fire first and once they
are all firing, the base load boiler would fire.
To minimize the cycling of a large base load boiler,
consider using the stop condition. Change it to the OA
T < 15F (Outside Air Temperature) condition. This
setting may be used to stop the priority 1 boiler set
when the OA T drops below the OA T setpoint, thus
leaving the large base loaded boiler on and shutting off
S T A R T P R I O R I T Y 1
> S E T : F I R S T
S T O P P R I O R I T Y 1
S E T : L A S T