OPTIONAL FEATURES
HeatNet Control V3 3.x
Page 77
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 water
flow are provided.
1.
Water Flow Limited Control (BMS)
2.
Boilers Limited Control (BMS)
3.
Water Flow Meter
The water flow settings are used to limit HeatNet’s ability to
add boilers when the system water 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 water 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 number 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.
Using these features can limit HeatNet’s
ability to maintain setpoint.
4.
Flow Limited Control
: This method helps HeatNet to
limit the # of boilers firing based on the System Water
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: