SETUP & OPERATION
HeatNet Control V3 3.x
Page 26
Using the boiler charts and the examples used in: Mixed
System Type 1: High System Turndown, a mixed hybrid
boiler system can be designed. The Priority 1 boilers should
be setup so as to keep the non-condensing boilers from
seeing return water temperatures of less than 140 degrees F
to ensure a long heat exchanger life.
Normally, the Priority 1 boilers will fire first. Once all the
Priority 1 boilers are firing, the next boiler to fire (after the
ADD BOILER timer expires) would be the Priority 2 (non-
condensing). If the return water temperature has not come
up to ~140F, the non-condensing boilers could fire in a
condensing mode. The ADD BOILER delay timer would
have to be set to a long enough period to ensure this does
not happen. Even then, the load may be too great. The
following note will explain an alternative way (not
depending on the ADD BOILER DELAY) to keep non-
condensing boilers from firing in a condensing mode.
When running with a remote BMS setpoint, care must be
taken that an Outside Air reset setpoint (or other setpoint)
sent by the BMS is not set too low. If the BMS system is
controlling the setpoint close to the condensing temperature,
the return water temperature may never rise sufficiently to
keep boilers out of a condensing mode. HeatNet online is a
good way to monitor this scenario if suspected.
If the firmware version for a HeatNet V2
board is at least 3.47(or a version 3 board),
the non-condensing boiler may hold itself off from being
added to the HeatNet MASTER’s available to fire list.
This would effectively keep the non-condensing boiler
from firing in a condensing mode, but as a result, may not
satisfy the system setpoint.
In order to use this feature, the version 2 board would
need to monitor the system or local return temperature.
This can be done locally by setting SETTINGS: HEAT
EXCHANGER: TEMPERATURE DISABLE: RETURN if
the there is no pump/valve limiting flow continuously
through the boiler. If there is a pump/valve limiting the
flow through the boiler, the SETTINGS: HEAT
EXCHANGER: TEMPERATURE DISABLE: SYSTEM
RETURN needs to be set. Then the MASTER boiler needs
to set SETTINGS: HEAT EXCHANGER: SEND RETURN
SENSOR: to which of its return temperatures it would
send to all boilers. These include the Local Return
temperature or the System Return temperature.
The MEMBER’s menu “SETTINGS: HEAT
EXCHANGER: TEMPERATURE DISABLE:” if set to
RETURN or SYSTEM RET, will force the boiler to
become unavailable to HeatNet when the SETTINGS:
HEAT EXCHANGER: TEMP< 140F. This value is
adjustable to 135F if a forced air fan is used. When the
SYSTEM RETURN or RETURN temperature is <140F the
boiler responds to a HeatNet MASTER’s request as”
unavailable”. As soon as the return temperature reaches
140F, the boiler will respond to the MASTER’s request
that it is available to fire.
If the MASTER boiler is a version 2 board, the MASTER
will always transmit its Local Return temperature to all
boilers. If the MASTER is set to Priority 1 and all other
non-condensing boilers are set to Priority 2, the MASTER
should always remain on if there is a call for heat. This
requires that the Priority 1 boiler be set up to start first
and stop last. Using this method should always send a
valid return temperature to the MEMBER boilers. This
method can also be used with a version 3 board, but a
system return sensor is preferred.
When this condition is in effect, the STATUS * screen will
indicate “blr offline”. While the boiler is in this “not
available” state, it can still be fired locally, and failsafe is
still available.
SETTINGS: HEAT EXCHANGER: SEND RETURN
SENSOR:
OFF
The MASTER sends its return
temperature to all boilers
RETURN
The MASTER sends its return
temperature to all boilers
SYS RET
The MASTER sends the
system return temperature to
all boilers
SETTINGS: HEAT EXCHANGER:
TEMPERATURE
DISABLE:
OFF
No check is made to the return
temperature – boiler remains
online
RETURN
Uses the boilers own return
sensor (No pump /valve
present)
SYS RETURN
Uses the System Return temp
received from the MASTER
Boiler (its Local or System
Return).
SETTINGS: HEAT EXCHANGER: HEAT EXCHANGER:
TEMP < 140F
Adjustable threshold temperature below which the
boiler will take itself offline.
(1) Degree F of hysteresis is provided so as to not
toggle offline<-to->online at the threshold temp.
Since the FIII boiler is non-condensing, the efficiency vs.
input is relatively flat. The MOD MAX value will not have
the same impact if the FIII non-condensing boilers were
placed in the Priority 1 set.