Heating Control Methods; Heating Method 1; Heating Method 2; Heating Method 3 - HydroTherm HeatNet KN -6 User Information

CONTROL METHODS

Heating Control Methods

An overview of the (5) methods for controlling the KN
series boiler are presented here. They are outlined in more
detail at the end of this section.

Heating Method 1

The first method is to use the KN Series boiler in its stand-
alone modulating method. This method uses a PID
algorithm to maintain a setpoint and is enabled using the
HEAT DEMAND input. Closing a relay contact or switch
across the HEAT DEMAND input will cause the Master
boiler to control all member boilers using H-Net.
A member boiler may also be controlled by the HEAT
DEMAND input (LOCAL mode). The member boiler will
then ignore commands from the Master and maintain its
LOCAL SETPOINT at the supply sensor.

Heating Method 2

The second method is to view the KN boiler as two separate
boilers or as a HIGH/LOW boiler using T1 & T2.

Heating Method 3

The third method is to allow a remote 4-20 ma or 0-10 VDC
signal to control the firing rate (modulation) of the boiler
using the 4-20ma input, along with the 4-20ma REMOTE
ENABLE input.

Heating Method 4

The fourth method turns the boiler ON and OFF @ 100%
modulation using the AA terminal.

Heating Method 5

The fifth method uses an RS485 digital communications
cable with the MODBUS protocol. The boiler is controlled
by writing and reading registers using MODBUS
commands. A bridge module may also be used to convert
BACnet or LonWorks protocols to MODBUS.
Short cycling may occur when a firing rate is
sent to a member boiler that would cause the
supply temperature to raise high enough to
trip the operating limit (low flow rate). After
the supply temperature falls, the boiler would
restart and the process may continue. A
member boiler would use its supply (outlet)
sensor to protect itself from short cycling by
limiting the firing rate coming from the
Master. This occurs in the event that the
member's supply temperature increases above
the (OPERATE LIMIT- OPERATE LIMIT
BAND).

Operating Limit

When the master boiler or an external control input is used
to control a member boiler (i.e. AA, T1-T2, 4-20ma, H-
Net), a software operating limit on the member boiler will
be used to limit the maximum output of the member boiler.
This operating limit can be adjusted in the
SETUP:SETPOINTS:OPERATING LIMIT.
There is also an associated operating limit band that must be
set in conjunction with the operating limit to help prevent
this LIMIT from being reached. Its purpose, is to limit the
output of the boiler as it approaches the operating limit. If
the band is set to 10 degrees, then for every degree that it
approaches the operating limit, the maximum output will be
lessened by 10%. With a band of 20 degrees, for every
degree that it approaches the band, the maximum output will
be lessened by 5%. You can think of this operating limit as
a smart aquastat which prevents the High Limit from
tripping. This method minimizes boiler short cycling when
using external inputs. The minimum setting is 1 degree and
effectively turns the limit band OFF. The default setting is
20F.

Input Priorities

The KN-Series control inputs are prioritized so that
multiple levels of external control can be employed at the
same time. This means that if we are firing the boiler with a
low Priority input and a higher Priority input is called for,
the boiler will now fire at the higher Priority input. When
the high Priority input is removed, the boiler will revert
back to the lower Priority input that is still being called.
Priority 1
The AA terminal has absolute control, and if used, will
always fire the boiler at 100% output, regardless of any
other input. The 4-20mA input may be raised to this
Priority using ADVANCED SETUP: 4-20mA
INPUT:CHANNEL MODE:PRIORITY.
HeatNet Control V3 2.x
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