CONTROL METHODS
HeatNet Control V3 3.x
Page 33
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 Control Input 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.
1.
Closing only one of these contacts tells the boiler to
operate at MINIMUM FIRE.
2.
Closing the other contact will fire the boiler at
MAXIMUM output (the same rate as closing the AA
input).
Figure 23
Stage Control Input
The maximum output of the boiler is based on
the
MAXIMUM %
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 Control Input 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