OPTIONAL FEATURES HeatNet Control V3
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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.
3. Flow Limited Control (BMS)
4. Boilers Limited Control (BMS)
5. 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 4-20 mA
(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 has the ability
to limit the # of HeatNet boilers allowed to fire. When a
system has a fixed amount of boilers that HeatNet reports are
available, the BMS can limit the # of boilers that can fire. The
BMS can write the GPM value it has for flow, or directly
write a register with how many boilers HeatNet can control. If
the BMS GPM flow feature is active, the direct control
becomes inactive.
Note: using these features can limit HeatNet’s ability to
maintain setpoint.
1. Flow Limited Control: This method helps HeatNet to
limit the # of boilers firing based on the System Flow in
GPM. In variable flow systems, this will limit HeatNet’s
ability to add new boilers when insufficient flow is
available. The # of boilers allowed to fire is determined
by:
# Of HeatNet boilers that can fire = BMS GPM Set Rate/
LOWEST FLOW
To activate this flow limited feature for use with a BMS:
b. Set SETTINGS: FLOW METER: ENSBLED? YES
c. Set ADVANCED SETTINGS: FLOW METER:
GLYCOL MIX ? %. Currently, any mix over 10%
de-rates the flow by 30% (rule of thumb method).
Example: if the LOWEST FLOW = 50 GPM, HeatNet
will calculate a New Lowest Flow required to be 65
GPM. The LOWEST FLOW does not need to be
changed, but is calculated to 65 GPM and that value is
used by HeatNet.
d. Set SETTINGS: FLOW METER: INPUT TYPE to
BMS.
e. Set SETTINGS: FLOW METER: LOWEST FLOW
(The automatic value loaded will equal the lowest
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