CONTROL METHODS
HeatNet Control V3
Page 26
Features of the HEAT DEMAND input include:
1.
The control is designed to
predict
when to start and
stop the boiler and keep the setpoint in, or as close to
the control band as possible. If PREDICTIVE START
is enabled, the boiler may start when it is in the band
and not below it. This will help to maintain a more
accurate temperature relative to the setpoint. See also:
SETTINGS: FIRING MODE: PREDICTIVE START:
to disable this feature.
2.
The control can also use the Outdoor Reset feature.
This feature allows the setpoint to be changed
automatically based on the outside air temperature. If
this feature is used, the control input: OR OVR
(OUTDOOR RESET OVERRIDE), can be used to
override the Outdoor Reset feature and run from the
local setpoint. A contact closure on the ‘AA’ input can
also override this method.
3.
The 4-20mA setpoint control function works in
conjunction with this mode. This function translates a
4-20mA control signal to a setpoint mapped between
50F and 220F. These (2) temperatures are adjustable to
provide a setpoint range. The minimum start current is
also adjustable between 3.71 and 5mA. The setpoint
control feature is used in conjunction with the
REMOTE ENABLE input on J12A. This feature is
enabled in the SETPOINTS menu as:
SETPT SOURCE 4-20mA
4.
There is also support for a common system damper,
Heat Exchanger support, and starting the Master first
for common venting. For an overview of each of the
menu settings see:
DEFAULT SETTINGS
section.
Heating Method 2
STAGE Control T1-T2
The boiler can also be operated in 2 separate stages using
the inputs T1 and T2 inputs. Its intended use is with an
external stage controller with no analog or modulation
outputs.
Closing only one of these contacts tells the boiler to operate
at MINIMUM FIRE.
Closing the other contact will fire the boiler at MAXIMUM
output (the same rate as closing the AA input).
Stage control input
The maximum output of the boiler is based on
the MAX VFD setting in the calibration mode
and not the nameplate rating.
The AA, HEAT DEMAND (LOCAL) input, the H-Net, the
4-20mA input will all override the stage control inputs.
Heating Method 3
4-20mA Control
Placing a current source between the + and – 4-20mA inputs
will allow remote control of the boilers firing rate. An
adjustable starting mA current signal here will start and then
fire the boiler at the minimum fire rate. See
: SETTINGS:
4-20mA INPUT: CHANNEL MODE
.
See section OPTIONAL FEATURES Using the 4-20mA
input
for extensive detail.
A 20mA signal will fire the boiler at the maximum firing
rate. The input current signal is viewed as a percentage to
the boiler from 0 to 100% (0-20mA). This means that a
20% (4mA) input signal is required to start the boiler, but
since the boiler is classified as having example: 4:1 turn
down ratio, the boiler can only be fired as low as 25% of
output. Any signal between 20% and 25 %, will fire the
boiler at the minimum fire rate. If the MINIMUM setting of
the boiler is set above the example: 4:1 turndown of 25%
(such as 33%), a control signal change between 25% and
33% will not change the boilers firing rate. Once the control
signal rises above the MINIMUM fire rate, the control
signal will then affect control of the boilers fire rate.
The AA terminal, the HEAT DEMAND, and the H-Net
NETWORK are the only inputs that will override the 4-
20mA input.
Method 2
Stage Control Inputs:
T1
&
T2
