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KN INSTALLATION AND OPERATION INSTRUCTIONS
The
K N
condensing cast iron boiler
Operation
Overview
The
K N
is a cast iron boiler designed and constructed to allow full condensing operation. The illustration
at left shows how the boiler is heated with a down-fired premix gas burner mounted above the heat
exchanger. The
K N
blower pulls gas and air through a venturi assembly and pushes the mixture into
the burner. The power of the blower forces the flue products through the heat exchanger and out the
vent.
Boiler operation is controlled with the
K N
electronic control. The control modulates boiler firing rate
based on system demand, allowing input as low as 20% of maximum (5:1 turndown). Combined with
the indoor or outdoor reset option of the
K N
control, this allows maximum possible condensing mode
operation, with thermal efficiency up to 99% at minimum input.
Cast iron heat exchanger
The
K N
cast iron heat exchanger uses graphite port seals and ground joint fit-up between sections for
maximum flexibility and resistance to thermal expansion. The heat exchanger provides maximum heat
transfer with its counterflow design and flow-controlling baffle assembly.
Premix burner
Premix means the air and gas are mixed before they enter the burner. The mixing of gas and air in the
blower and piping ahead of the burner causes a uniform gas/air mix in the burner, providing reliable
operation with low excess air. The result is exceptional combustion efficiency.
The burner consists of a high-temperature stainless mesh secured to a stainless steel distributor plate. The
design causes uniform flame across the entire surface of the burner and the ability to operate at very low
firing rates. The flame is ignited with direct-spark electrodes and an electronic ignition control. Flame is
proven using a flame rod (flame rectification sensing).
Because of its low excess air operation and controlled combustion, the burner also provides low NO
X
emissions and quiet operation.
Gas valve, blower and venturi
Most gas valves regulate at a positive pressure downstream of the valve (typically 3½ inches water
column). But the
K N
gas valve regulates to ZERO pressure downstream. This is called a “zero governor”
valve. The advantage is that gas will only flow if something lowers the pressure downstream of the valve
below zero. That is just what happens when the blower pulls air through the venturi. As the air speeds up
to pass through the narrow throat of the venturi, a vacuum forms in the throat. The more air that flows
through the throat, the greater the vacuum.
The gas valve raises the negative pressure in the venturi to zero by letting gas flow. The lower the pressure
in the venturi throat, the more gas will that will flow. So gas flow automatically adapts to air flow, ensuring
consistent gas/air mix throughout the boiler’s modulating range. Thus, the
K N
HeatNet® electronic
control regulates the blower speed to control boiler firing rate.
K N
HeatNet® control
The
K N
HeatNet® electronic control consists of a microprocessor-based module and a keypad/display
unit for user interface. The control regulates boiler water temperature by adjusting boiler firing rate (by
varying the blower speed). The control considers how fast the temperature changes and how the
temperature varies over time to establish the best firing rate to meet demand. Options include an outdoor
sensor for outdoor reset operation and an indoor reset option. (Indoor reset monitors up to 8 zone
thermostats and determines a maximum firing rate needed to meet the demand. This keeps the boiler at
the highest possible efficiency.) In addition, the control can be set for multiple boiler operation, either
stand-alone or utilizing on-board HeatNet® technology. The control also automatically cycles the factory-
installed postpurge circulator to equalize residual heat in the boiler after firing.
K N-2