RBI FUTERA XLF Series, Control Manual

Page: 19 / 128

SETUP & OPERATON HeatNet Control V3
Page 19
Figure 13 Mixed Condensing/Non-Condensing Boiler
System
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MASTER
Condensing
MEMBER 1
Condensing
HNET HNET
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HNET
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MEMBER 2
Non-
Condensing
MEMBER 3
Non-
Condensing
Priority 1 Set Priority 2 Set
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Outdoor Air
Sensor
Figure 14 Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
Priority 1
CB/CW 4:1
Priority 2
MB/MW
4:1
4.5 24:1 60% 750, 750
1000, 1000,
1000
4.75 32:1 60% 500, 500
1250, 1250,
1250
6.5 26:1 65% 1000, 1000
1500, 1500,
1500
6.0 48:1 65%
500, 500,
500
1500, 1500,
1500
For the examples, the RBI FIII/Fusion series water heaters
will be used. These boilers are non-Condensing, fully
modulating, low mass, and HeatNet compatible.
The Mixed Boiler System table show some examples of
mixed systems using different sizes along with Fusion
condensing (Priority 1) and Futera III non condensing
(Priority 2) boilers.
Using the boiler charts and the examples used in: Mixed
System Type 1: High System Turndown, a mixed 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 140F 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 SETUP: AUX
FUNCTIONS: HEAT EXCHNAGER: TEMP DISAB:
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 SETUP: AUX
FUNCTIONS: HEAT EXCHNAGER: TEMP DISAB: SYS
RET needs to be set. Then the Master boiler needs to set
SETUP: AUX FUNTIONS: HEAT EXCHNAGER: SEND
RETURN: 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 “SETUP: AUX FUNCTIONS: HEAT
EXCHNAGER: TEMP DISAB:” if set to RETURN or SYS
RET, will force the boiler to become unavailable to
HeatNet when the SETUP: AUX FUNCTIONS: HEAT
EXCHNAGER: TEMP< 140F. This value is adjustable to
135F if a forced air fan is used. When the SYS RET 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