OPTIONAL FEATURES
HeatNet Control V3 3.x
Page 65
For
system pump modulation
a 0-10Vdc control signal
output is provided at J4.3 (signal) and J4.7 (ground). This
signal is output by the MASTER boiler as a percent function
of the number of boilers running and can be used to set the
speed of a System Pump using a Variable Frequency Drive.
Two wires are required and need to be inserted into the J4.3
and J4.7 positions to access this signal.
This signal has a step response and is not linear
to the system or boiler’s input firing rate.
The output signal is proportionally mapped to % using the
equation:
%VFD = (boilers running/total boilers)
The %VFD represents the stepped percentage of boilers
running where:
0Vdc = 0% (to) 10Vdc = 100%
If there are (6) boilers in a system and (2) are running, the
control signal = 33% or 3.3Vdc. This signal could then be
applied to a system pump’s VFD to control the speed of the
pump relative to how many boilers are firing. The VFD would
need to be set appropriately to allow the correct flow through
each boiler.
In low volume systems sudden temperature changes may
occur when the flow is stepped up or down by a large
percentage. In these situations, the SETTINGS: ADAPTIVE
MODULATION: MODULATION MODE may need to be
changed from ADAPTIVE and the ORIGINAL KN method
used. Other adjustments may also be required.
Currently, no failsafe mode is available in the event the
MASTER boiler’s control fails. If this method is employed, a
failsafe boiler could be used to override the control signal and
enable the system pump’s VFD using some external wiring
and an external relay or have the VFD default to a safe speed
on loss of the control signal.
If (2) pumps are available, pump rotation is available. The
rotation of the (2) pumps can be controlled using two
methods.
1.
Pumps are switched based on the system run time
2. Pumps are switched by the difference between each
pump’s runtime. The HeatNet control keeps a running
record of each pump’s runtime in hours. If a pump is
taken offline or replaced. The runtimes can then be
adjusted until they become equal.
These features may be selected in the menu, SETTINGS:
SYSTEM PUMP: PUMP ROTATION
Local Pump Options
The
local circulator pump
is supported by (3) modes and (2)
features.
1.
The first mode allows the circulator pump to remain on,
unless the controls outside high air temperature setting
has been met when using Warm Weather Shutdown.
2.
The second mode will allow the circulator pump to be
turned on whenever there is a call for heat (any control
input). This mode will stop the circulator pump when the
call for heat is lost, and the pump post purge time has
been satisfied.
3.
The third mode works much the same as mode 2, but it
allows the inlet sensor (RETURN) to be used with the
outlet sensor (SUPPLY) to keep the pump on until a delta
(difference) temperature is met. A return temperature
sensor is required for this mode, because the delta
temperature (SUPPLY – RETURN) measured is across
the boiler. In this mode, the post purge time is also used.
After the delta temp has been met, the post purge time
needs to expire before the pump is turned off. This mode
works much the same as mode 2.
MASTER PUMP/VALVE REMAINS ON
: This is a special
feature of the local circulator pump to prevent deadheading
water flow when all boilers are off. When this feature is
enabled, the MASTER boiler will enable its local circulator
pump/valve when
NO
boilers are running. If boilers are
running in LOCAL override and not controlled by H-NET,
but are visible to H-NET, the pump(s) on these boilers are
presumed ON. In this situation, the MASTER
will not
enable
its circulator pump/valve unless it is running.
Master Valve Remains Open Update
If the boiler was not firing, the local pump/valve post
purge time reduced to 30s, instead of the full post purge
time, and the flow prove time maximum is increased to
600s to allow for longer valve stroke times.