OPTIONAL FEATURES HeatNet Control V3
Page 69
control) is reloaded. If the setpoint timer is not written, a
default timeout value of 60 seconds is assumed. The
timer is automatically reloaded with the default value
when a setpoint is written.
The BMS mode is always on by default. To
disable or change the time watching the BMS
communications, go to the Setpoint Timer item
in the Communications menu.
SETUP: AUX FUNCTIONS: FAILSAFE MODES.
2. HeatNet Communications Lost
SETUP: AUX FUNCTIONS: FAILSAFE MODES: H-
NET COMM LOST
This mode allows a member boiler to run in LOCAL if
the communications link via the H-NET cable is lost.
This includes the MASTER boiler losing its Control
board, Communications board, or the power on the
MASTER is switched OFF. When this MODE is set to
ON, and if the member boiler loses its link (heartbeat
packet over the H-NET cable) to the MASTER Boiler,
this MEMBER will fire to the LOCAL setpoint.
The heartbeat packet over the H-NET cable
needs to be lost for 10 minutes.
This MEMBER boiler will continue to run at the LOCAL
setpoint until H-NET communications from the
MASTER boiler is re-established.
Ensure that this Member boiler’s Damper and System
pump control are configured correctly with the
assumption that the Master is not powered. Also ensure
that any other System settings related to outside air
temperature sensing and system interlocks are set to
provide safe operation. Domestic Hot Water can also be
provided using this mode. See the DHW section of this
manual.
3. Low Temperature Protection
LOW TEMP: OFF, SUPPLY, HEADER, DHW, or
RETURN
This mode may be used by the MASTER or MEMBER
boiler and can be used as a type of freeze protection. In
this mode you may select which Sensor you wish to
monitor, or you may opt to turn this mode OFF. If you
select a sensor, you may then associate it with a
temperature at which the boiler will turn ON. Once the
temperature at this sensor falls below the LOW TEMP
temperature the boiler will start and fire to its LOCAL
setpoint. Once the Boiler reaches its setpoint it will turn
OFF.
4. Using the Base Load Relay
If there are no boilers available to fire (offline or faulted)
and there are no boilers in local override, and there is a
call for heat, The J4 Base Load relay will close. If a
boiler becomes available and needs to fire, the Base Load
boiler will remain firing until the temperature exceeds the
band. This is provided to keep the system from entering a
no heat situation.
Limited Flow Boiler Control
Options
Three methods to limit the boilers operation based on flow are
provided.
1. Flow Limited Control (BMS)
2. Boilers Limited Control (BMS)
3. System Flow Meter
The flow settings are used to limit HeatNet’s ability to add
boilers when the system flow changes. In variable flow
systems, and when the system flow is reduced, any boiler(s)
that is/are running may develop a high delta temperature
across the boiler. When this occurs, the boiler(s) will enter a
high delta T protection mode and drop to half of the rate
called for. At this time, the Master may not be able to achieve
setpoint due to the reduced output with the running boiler(s).
The Master will then call on more boilers to achieve setpoint,
but at the same time splitting the flow through the boiler(s) it
has running. The flow can be so reduced that the boiler(s) trip
their operating limits or even their high limits.
A flow meter input is supplied on the analog input 4-20mA
(2). This input can be configured to capture flow in the system
that will be used to limit the # of boilers to fire. If a flow
meter and a System Return sensor are present, a BTU load
measurement will be displayed in the running screen. The
BTU value is relative to the accuracy of the sensors, the gas
BTUs, the flow sensor accuracy, and is only available as an
estimate of the BTU load. A calibrated BTU meter would be
required to get a more accurate measurement.
The BTU load value may also be accessed through Modbus
read registers 30242 (upper 16-bit word) & 30243 (lower 16-
bit word). These two words will need to be combined in order
to get the BTU load value.
When using the BMS GPM register the BTU values are only
calculated to a whole GPM since the BMS GPM register
currently does not support floating point numbers.
The Building Management System (BMS) also can limit the #
of HeatNet boilers allowed to fire. When a system has a fixed
number of boilers that HeatNet reports are available, the BMS
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