Start/Stop Priority Conditions - HydroTherm HeatNet KN -6 User Information

SETUP & OPERATION

Start/Stop Priority Conditions

The following is an example using mixed
condensing and non-condensing boilers:
FIRE FIRST
Condensing boilers may be configured to fire first (set to
PRIORITY 1) when:
2. The Return water temperature is below 140F and
condensing occurs. (The Master's return water sensor
would need to be moved to the header return.)
3. The Outside Air Temperature is above a setpoint
determined by the system configuration. This setpoint
ensures that the more efficient condensing boilers run
first during shoulder months (Spring and Fall) when
minimal heating is required. Below this setpoint, larger
boilers should be brought on first to ―base load‖ the
system.
4. Greater efficiency is required.
STOP FIRST
Condensing boilers may be configured to stop first (set to
PRIORITY 1) when:
The Return water temperature is above 140F and
condensing is minimized, thus leaving the larger lower cost
boilers running to carry the load.
1. 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.
2. 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. A System Return
sensor will be required. However, the return temperature
sensor may have been moved on the Master to provide
system return temperature on existing installations and is
still supported).
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:
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
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.
HeatNet Control V3 2.x
Page 13