Furnace Theory Of Operation - ICP N9MP1 Service Manual

Single Stage Multi Position Furnace
Figure 1
Component Locations for Four Position Furnaces
Furnace Vent Pipe
Vent Pipe
Grommet
Manual Gas Valve
Gas Valve/Ignition Module
Vent Drain Fitting
Diagnostic Light
Combustion
Blower
5
/ ² OD Vent Pipe
8
Drain Hose
3
/ ² OD Transition Box
4
Drain Hose
D
oor Interlock Switch
Fan/Delay Control

3. FURNACE THEORY OF OPERATION

The high efficiencies and lower profile (compared to previous
series) of this furnace have been obtained using design tech-
niques not typical of traditional furnace designs. A brief de-
scription of these new design techniques and the purpose
they serve follows.
1. Reducing the height of the furnace while maintaining
the high efficiency of pervious models required main-
taining the surface area of the heat exchanger and yet
minimizing the overall size.
The design required to achieve these results is the "SER-
PENTINE" design, wherein the flue gasses must follow a
serpent shaped passage through the heat exchanger via
convection.
This "Serpentine" path is resistive to normal convective flow,
and requires that a partial vacuum be created at the outlet
of the heat exchanger to maintain the flow of flue products
through the heat exchanger.
2. The serpentine heat exchanger design does not lend
itself well to the ribbon type, or slotted port type burner
found in more traditional design furnaces for the follow-
ing reasons:
A. The secondary combustion airflows at right angles
to the burner flame, making it likely to "pull" the flame
off a ribbon or slotted port type burner.
Rating Plate
Air
3
(Dual Certified or Direct
dwg 25--23--29a
B. The flame "height" of a ribbon or slotted port type
burner would make it difficult (if not impossible) to
prevent impingement of the flame on the heat ex-
changer surfaces whole maintaining the low profile
heat exchanger.
For these reasons, an "INSHOT" type burner is used in this
series. The inshot burner (also called a "jet" burner) fires a
flame straight out its end. This burner is designed to fire into
a tube style heat exchanger, making it an ideal application in
the tube--like passages of the serpentine heat exchanger.
3. In order to extract the maximum amount of heat pos-
sible from the flue gasses, a secondary heat exchang-
er (condenser) is connected to the outlet of the primary
heat exchanger. This condenser removes additional
heat from the flue gasses, causing their temperature to
drop below dew point. This results in the forming of
condensation (water) which then must be routed to a
drain.
4. The placement of the secondary heat exchanger at the
outlet of the primary heat exchanger creates additional
resistance to the flow of gasses.
5. To overcome the resistance to convective flow of the
Primary and Secondary heat exchangers requires the
use of an Induced Draft Combustion Blower Assembly.
Service Manual
Air Intake Pipe
Vent Model)
Primary Heat Exchanger
Secondary Heat Exchanger
Pressure Switch
Plastic Transition Box
Circulating Air Blower
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