CONTROL METHODS HeatNet Control V3
Page 37
This Method highlights the flexibility of the HeatNet
system. It works much the same as DHW METHOD 1,
but also has the ability to provide space heating and
failsafe functions. With a three boiler system, and with
any one boiler down, the system can still provide space
heating and a DHW call seamlessly.
With this method the Master boiler will use two PID
controls to simultaneously maintain the DHW and space
heating setpoints. This method is determined by
SETTINGS: DISTRIBUTED CONTROL: MASTER
TYPE: Combination.
This method utilizes a 10k thermistor connected to the
DHW Sensor input and the HEADER sensor input of a
MASTER boiler. Setting up the DHW portion of this
method is done via the menus in: SETTINGS:
DOMESTIC HOT WATER. For information on setting
up the space heating portion of this method, Refer to Heat
Demand Control Method 1 located in the CONTROL
METHODS section.
When this method is used (due to use of the DHW sensor),
the OR OVR input functions as an enable/disable. This
allows the DHW heating function to be enabled or
disabled much in the same way as the Heat Demand input
for space heating.
The DHW pump is individually controlled on each boiler
that fires in DHW. The Master does not use its pump
globally when any DHW boiler is called. The Master only
engages its DHW pump if it was called to perform DHW
heating.
When using this method, a DHW band is also available in
the Home screen. The space heating band will be
displayed on the left and the DHW Heating band on the
right. The bands will operate in a split screen view.
When using MASTER TYPE: COMBINATION, the
Master may control DHW and Space Heating needs. If the
Master goes down or loses communication with the
Member, a Failsafe mode is available to provide temporary
heat.
The DHW Failsafe mode is active when a Member
boiler’s SETTINGS: FAILSAFE MODES: H-NET
COMMUNICATIONS LOST: is set to ON. When this is
set to on, normal DHW heating using the OR OVR or DHW
sensor is disabled, even though there may be a DHW call on
one of these inputs.
When the Master Boiler’s communication is lost, and
after 10 minutes of not being restored, the DHW inputs
become active. The boiler now enters a stand-alone mode.
The Heat Demand on that boiler becomes active and not
only runs to provide failsafe space heating, but DHW heat
as well. The STATUS screen will display H-NET LOST.
If a thermostat is used, the boiler will run to Method 5A
until the thermostat input removes the DHW call. If a DHW
temperature sensor is used, the boiler will modulate to
maintain tank temperature. The DHW Call always has
priority over space heating. A dual 10k sensor is available
that can be wired from one tank to two boilers.
The DHW Method 2 examples uses (3) boilers. The
Master controls the Space and Domestic needs, though it
is not a DHW boiler. Failsafe control is provided by
wiring the Member boiler to the tank sensor (dual sensor
is optional) and any other system control needs the
Member may require in its backup role. Then one of the
local DHW control methods can be used to implement
DHW heating.
One advantage to this configuration is that a BMS can
control the system through the Master. It can also monitor
system status through a central location (Master boiler) by
a BMS, or HeatNet Online. This failsafe method can also
be used in the Combination DHW/Space Heating
Simplified Drawing.
Set up the Master boiler first:
1. Connect a 10k thermistor from the DHW tank’s
sensor well to J10B terminals on the MASTER, and
connect a Header Sensor to the SYSTEM HEADER
input. Wire any pump or valve from the DHW Pump
relay’s (normally open) contact to control flow of the
heating water into the tank’s coil or DHW loop.
2. Now, set the SETTINGS: DISTRIBUTED
CONTROL: MASTER TYPE: to Combination.
This setting informs the HeatNet control that (2) PIDS
are to be used to control DHW and space heating.
3. There are two MODULAR BOILER menus, one for
space heating and one for DHW heating. These (2)
menus appear when the SETTINGS:
DISTRIBUTED CONTROL: MASTER TYPE is
set to Combination. The (2) Modular boiler settings
are located in the SETTINGS: MODULAR
BOILER: menu. Normally, there is only one, but
with (2) independent PIDs, the (2) heating setpoints
may behave differently due to their loads or for other
various reasons. These allow for separate ADD,
SHED, MODULATE DELAY TIME, and
MODULATION MAXIMUM settings for DHW
and space heating.
4. Next, enter the SETTINGS: DOMESTIC HOT
WATER menu. When prompted for BOILER
MODE enter OFF.
5. Change the DHW SETPOINT to the desired target
temperature of the water in the tank/ or DHW loop.
Once the control determines there is a call for DHW
heat, the DHW PID will target this SETPOINT.
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