Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to smoke detectors and, in
particular, smoke detectors adapted to control the operation
of a furnace.
Smoke detectors for use in homes and offices are well
known and the purpose of such detectors is to sound an alarm
when a certain level of smoke is detected in the air
surrounding the detector. A common form of smoke detector is
the ionization type but other types are known. Often smoke
detectors are battery operated so they need not be hooked up
to electrical circuitry in the building and are able to
operate independently. Generally said detectors are mounted
on the ceiling of a room or hallway and it is often
recommended that a detector be located on each floor of a
building or residence.
United States patent No. 4,171,944 issued October 23,
1979 to J.B. Hirschm~nn teaches the use of a combined smoke
detector and furnace shut-off device wherein the smoke
detector is mounted to the wall or ceiling of the furnace room
or possibly in one of the hot air ducts leading from the
furnace. The purpose of this smoke detector is to sense the
presence of smoke unnaturally expelled from the furnace into
the furnace room or the hot air duct. When the smoke detector
senses smoke, a signal is sent through a wire to an electrical
relay connected to the ignition electrodes of the furnace,
effectively shutting off the electrical supply to the ignition
device. In addition, the smoke detector is able to generate
; a signal to operate a solenoid valve to shut-off the supply of
fuel to the furnace.
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There are several perceived difficulties with the smoke
detection device taught in the aforementioned patent
specification. One such difficulty is that if the smoke
detector is mounted in the furnace room and not in any air
duct, it will not detect any smoke that is entering into or
passing through the furnace but which is not escaping from the
furnace. Thus, the furnace may continue to operate even
though there may be a fire in or smoke in other rooms in the
house or building.
A second difficulty with the Hirschmann device is that,
even if smoke is sensed by the device, the device will only
shut-off the ignition mechanism for the furnace and perhaps
also the supply of fuel to the furnace and this may permit the
blower in the furnace to continue to operate. Experts in fire
fighting note that a furnace fan or blower which continues to
operate after a fire has started can only make matters worse
by both distributing smoke to other rooms in the house through
the duct system and by feeding the fire with the fresh air
that it needs to sustain combustion and grow.
Even if the smoke detection mechanism is mounted in the
hot air duct of the furnace rather than in the furnace room,
the Hirschmann device may not operate satisfactorily. One
reason for this is that the very hot air that enters a hot air
duct from a furnace is too hot for most standard smoke
detectors and would quickly cause the smoke detector to fail
or to simply not operate. Another difficulty with the
Hirschmann proposal is that any smoke returning to the furnace
through the return air duct may not be passed into the hot air
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duct in which the smoke detector is mounted and this would
result in the smoke detector failing to operate even when
there is smoke being circulated in or being generated in the
house. Also, Hirschmann teaches no mechanism or system for
drawing an adequate sample of air that is passing through a
hot air duct to the smoke detector. For example, it is
possible that smoke could pass through the hot air duct
containing the smoke detector yet never come into contact with
the smoke detector (for instance, the smoke might be blown
past the smoke detector on the opposite side of the duct due
to the arrangement or layout of the duct).
Recent U.S. patent No. 5,239,980, issued August 31, 1993
to F. E. Hilt et al., describes a forced air furnace control
system for preventing the build up of dangerous concentrations
of CO gas within a building. A CO sensor is mounted in the
air exit plenum of the furnace and is connected in a circuit
which produces an output signal when the concentration of CO
gas in the plenum reaches an unsafe level. A disable control
signal is then triggered through the circuit for switching the
furnace off.
U.S. patent No. 2,727,203 issued December 13, 1955 to
Heat Timer Corporation describes an apparatus for detecting
the presence of smoke in a chimney and subsequently shutting
off a burner unit. This system employs an electronic control
that becomes non-conductive with the presence of smoke to in
turn de-energize a relay and initiate the operation of a
- timer/burner/motor shut-off.
The present invention provides a unique smoke detection
211919~
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apparatus designed for use in conjunction with a return air
duct of a furnace. The smoke detector is able to detect the
presence of smoke in an air sample drawn from the return air
duct. If a certain level of smoke is detected, an alarm
device connected to the smoke detector will sound an alarm
and/or the apparatus will act to shut down the furnace and
this may include both its ignition device and a blower or fan.
According to one aspect of the invention, a smoke
detection apparatus comprises a housing adapted for mounting
on the exterior of a return air duct for a furnace and smoke
detection means for detecting the presence of smoke in the air
present in the housing, the detection means being mounted in
the housing. There are also means for drawing a small portion
of air in the return air duct into the housing. An alarm
device is electrically connected to the smoke detection
mechanism and is controlled thereby so that the alarm device
sounds an alarm when the smoke detection mechanism senses a
predetermined level of smoke in the air present in the
housing.
In the preferred apparatus disclosed herein there are
also means for shutting down the furnace, including its
ignition device and blower.
According to another`aspect of the invention, a combined
smoke detection and furnace shut-off apparatus includes a
smoke detector for sensing the presence of smoke in air and
means for mounting this detector adjacent a return air duct
for a furnace. There is also means for conducting a portion
of air in the return air duct to the smoke detector. An alarm
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device is electrically connected to the detector and is
operated thereby so that the alarm device sounds an alarm when
the smoke detector senses smoke in said portion of air and
generates an alarm signal. There are also means for shutting
down at least an ignition device and a blower of the furnace
when a shut down signal is generated by the smoke detector.
This shutting down mechanism is electrically connected to the
smoke detector.
According to a further aspect of the invention, a furnace
shut-off apparatus includes a smoke detector device for
sensing the presence of smoke in an air sample taken from air
in a return air duct for a furnace and a mechanism for
shutting down the furnace when the smoke detector device
senses a predetermined level of smoke in the air of the return
air duct. The shutting down mechanism is electrically
connected to the smoke detector device.
Further features and advantages will become apparent from
the following detailed description taken in conjunction with
the drawings.
In the drawings,
Figure 1 is a perspective view of the top portion of a
typical furnace equipped with a smoke detection apparatus
constructed in accordance with the invention;
Figure 2 is a cross-sectional elevation taken through the
~ 25 axial centre of an air intake pipe of the smoke detection
- apparatus;
Figure 3 is a detail view in elevation, and partly in
cross-section, showing the mechanism for returning sampled air
2119194
to a hot air duct of the furnace;
Figure 4 is a detail view showing a block connector that
can be used to connect the apparatus of the invention to a
furnace control box; and
Figure 5 is an electrical circuit diagram illustrating
the preferred form of electrical circuit for a combined smoke
detection and furnace shut-off apparatus constructed in
accordance with the invention.
Shown in Figure 1 is a standard forced furnace 10 which
may be fuelled typically by natural gas or fuel oil. As is
well know, these furnaces are equipped with a suitable
ignition device (not shown) and a blower or fan for
circulating air through the furnace. As illustrated, incoming
; air enters the top of the furnace through a return air duct- 15 12. It will be appreciated that this return air duct is
connected to various rooms or hallways in the house or
building by ductwork so as to enable the air in these rooms
and hallways to return to the furnace where it can be
reheated. The returned air passes through a suitable heat
; 20 exchanger in the furnace and then the hot air is delivered to
the rooms in the house or building by means of one or more hot
air ducts 14.
Such furnaces are normally electrically operated and are
provided with power through a main power supply line indicated
at 16. This line is connected to a furnace control box 18
which is typically mountèd on one side of the furnace or
inside the exterior walls of the furnace. It will be
understood that this control box provides electrical power to
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all of the electrically operated components of the furnace
including an ignition device, a fuel pump (if required) and a
blower or fan.
A preferred form of smoke detection apparatus constructed
in accordance with the invention is indicated generally at 20.
It includes a box-like housing 22 which is adapted for
mounting on the exterior of the return air duct 12. As shown
in Figures 1 and 2, the housing can be provided with top and
bottom connecting flanges 24 and 26 and sheet metal screws 28
can be used to connect these flanges to the side of the duct.
As shown, the housing includes a top wall 30, an outer wall
32, a bottom 34 and two smaller, vertical sidewalls 36. The
housing is equipped with a further wall 38 which faces the
adjacent duct wall and which has a circular opening at 40.
15Mounted inside of the housing is a suitable smoke sensor
or smoke detector 42 which senses the presence of smoke in air
present in the housing. This smoke detector 42 can be of
standard, known construction and therefore a detailed
description of the detector herein is deemed unnecessary. For
example, it can be a standard ionization type detector or a
photoelectric smoke detector. This detector can be provided
with suitable electrical power through an electrical cord 44
that extends out of the housing. If, for example, the
; detector operates with 12 volt power, a standard step-down
transformer 46 can be connected to the cord 44. This
transformer has plugs at 48 for plugging the transformer into
a standard wall socket capable of providing 120 volts.
The apparatus 20 is equipped with means for drawing a
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small portion of air from the return air duct into the housing
22. The preferred drawing mechanism, as illustrated, is a
perforated air intake pipe 50 having a closed end 52 and an
open end at the aforementioned opening 4D in the housing.
This suction tube is preferably made of a suitable rigid
plastic but it could also be made of a metal such as steel or
tin. This pipe is adapted for insertion into the return air
duct and generally would have a length sufficient to extend
substantially across the width of the return air duct. In one
preferred embodiment, this pipe is about 12 inches long and
has an external diameter of about 2 inches. Preferably, in
order that the pipe will have an even draw across the duct,
the pipe is provided with either more openings S4 at its end
closer to the smoke detector housing than at its opposite end
or it is provided with larger openings at the end closer to
the housing. It will be understood that the pipe opens into
a sample chamber 56 formed by the housing.
Preferably there is mounted on the pipe 50 an air filter
58 which, in one preferred embodiment, is a broken cell
plastic foam filter in the form of a sleeve. The preferred
illustrated filter extends around and along the length of the
pipe 50 and thus the filter also has a length sufficient to
extend substantially across the width of the duct. In one
preferred embodiment the filter sleeve has an internal
diameter of 2 inches and an outer diameter of 3 inches. It
will be understood that there is cut or otherwise formed in
the air duct wall 60 a circular opening 62 having a diameter
large enough to permit insertion of both the pipe 50 and its
2~1919
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surrounding air filter 58. It will be understood that the
purpose of the filter 58 is to remove large particles from the
sample of air being drawn into the housing 22. This will help
ensure that such particles do not interfere with the operation
of reduce the life of the smoke detector 42.
It is highly advantageous to have an air sampling pipe
such as the perforated pipe 50 that extends across the width
of the duct. This helps to ensure that any smoke passing
through the return air duct will be drawn into the pipe and
sensed by the smoke sensor 42. If there was only a simple
opening 62 cut in the return air duct for sampling purposes,
it is quite possible that smoke could pass down through the
return air duct, for example on the side opposite the opening
62, and not be drawn into the housing 22. Thus, the use of
the sampling pipe 50 helps to ensure the reliability of the
smoke detection apparatus.
Also part of the drawing mechanism is a conduit or pipe
66 which is connected to the housing 22 and is adapted for
connection to an adjacent hot air duct such as illustrated
duct 14. It will be appreciated that there is a low pressure
region created at the outlet 68 of the pipe 66 by the
relatively fast moving hot air in the duct 14, which air is
being blown through the duct by a blower or fan in the
furnace. The direction of movement of this hot air is
indicated by the arrow H in Figures 1 and 3. It is because
the air in the housing 22 is drawn out of the housing through
the pipe 66 that air is drawn into the housing via the
sampling pipe 50. Instead of using the pipe 66 and the hot
211919~
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air duct, it would also be possible to force air out of the
housing 22 through an opening therein by means, for example,
of a small fan or blower. However, this solution could be
more expensive to construct and to maintain and operate over
a long period of time. Moreover, if a fan is used, in order
that the fan would not operate unnecessarily, for example,
when the furnace itself is not operating, it may be desirable
to provide an electrical control mechanism whereby the fan for
the smoke detection apparatus would only operate when the
blower or fan in the furnace is operating.
In a preferred embodiment, a pivoting damper is provided
at the intake opening of the housing 22. This damper can be
of standard design and is very simple in its construction. It
is manually adjusted by the installer of the present smoke
detection apparatus. It is mounted on the side of the housing
22 with its pivot pin projecting through the side of the
housing where it can be turned to make an adjustment. The
damper is normally set to permit an air flow of between 150
and 200 cu. ft. per minute. The liquid filled nonometer of
standard construction and mounted on the housing can be used
to set this air flow, which operation is done when the furnace
is turned on and running.
; In one preferred embodiment of the invention, the pipe 66
is a one inch flexible plastic pipe that is attached to the
hot air duct by means of a plastic flange connector 70 that is
connected to the wall of the duct by means of sheet metal
screws 72. In the illustrated preferred embodiment, the
flange connector includes a plastic air deflector 74 that acts
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to deflect the returning air from the pipe 66 in the direction
of the hot air passing through the duct. Thus, in the
illustrated embodiment of Figures 1 and 3, the deflector 74 is
arranged to deflect the sampled air upwardly.
The preferred smoke detection apparatus of the invention
includes an alarm device 76 that is electrically connected to
the smoke detector or smoke sensor 42 and controlled thereby
so that the alarm device sounds an alarm when the smoke
detector senses a predetermined level of smoke in the air
present in the housing. Except for the manner in which the
alarm or buzzer is mounted, the alarm device can be of
standard construction and similar to those used in previously
known smoke detectors. However, in the preferred embodiment
of the invention, the alarm device 76 is adapted for mounting
on a hot air duct such as the duct 14. In this way, the sound
made by the alarm will readily travel through the hollow hot
air duct or ducts so that it can be heard at various locations
and on different levels of the housing or dwelling. Although
it is possible to mount the alarm device 76 right in the hot
air duct, in the illustrated embodiment it is hard mounted to
the plastic flange connector 70 on the outside of the hot air
duct. Even in this outside position, testing has shown that
the sound caused by the alarm readily travels through the hot
air duct to distance locations in the house or building. The
alarm device 76 is connected to the smoke detector by an
electrical wire 78 of sufficient length to reach between the
housing and the location of the buzzer on the hot air duct.
It will be understood that the alarm device is actuated and
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sounds an alarm when the smoke detector or sensor 42 senses
smoke in the sampled air and generates an alarm signal.
In the preferred combined smoke detection and furnace
shut-off apparatus of the invention there is also means for
shutting down the furnace 10, including an ignition device and
a blower thereof. This shutting down mechanism indicated
generally at 80 is connected to the smoke sensor 42 and
controlled thereby. The shutting down mechanism operates to
shut down the furnace when the smoke detector senses a
predetermined level of smoke in the air present in the
; housing. Generally speaking, this would be the same level of
- smoke that sets off the alarm device 76. The preferred
shutting down mechanism, when activated, breaks a power line
L1 which is part of supply line 16, providing electrical power
to the furnace. The shutting down mechanism includes an
electrical lead 82 extending from the housing 22 and the smoke
sensor therein to a line connector 84 illustrated in Figure 4.
In a typical furnace installation having a furnace control box
; 18, the apparatus of the invention is connected into this
control box by first disconnecting the main power lead L1 from
the control panel in the box. It is then simply necessary to
connect the connector block 84 by pushing in the plug or jack
86 that extends from one side of the block. The plug or jack
86 is connected at the location where L1 was connected. The
line L1 is then inserted into and connected to the block 84.
The lead or line 82 is connected to a suitable latching relay
46 located in the housing 22, which relay is illustrated
schematically in the circuit diagram of Figure 5.
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Although the illustrated embodiment of the smoke
detection apparatus 20 is provided with electrical power from
a wall outlet, it will be understood that the apparatus could
also be provided with power from one or more batteries in the
same manner as known smoke detectors.
The two electrical leads extending between the connector
84 and the junction box 90 in the housing 22 can comprise BX
cable. By means of this cable, the 120 volt power supply
coming in through line 16 is rerouted to an inlet connection
of the junction box. The second lead 82 connects a power
outlet side of the junction box to the control box 18, thereby
normally providing electrical power to the furnace components,
including its blower and ignition device.
In the electrical circuit diagram of Figure 5 the wall
socket power pack that provides power to the smoke detector 42
includes a four-way bridge 102 to rectify the alternating
current and provide the DC power supply. Connected to this
bridge is a resistor 103, which can be a lK resistor, which
acts to limit current to the LED. Connected to the resistor
is an LED 105. Also connected to the resistor is a capacitor
98 to smooth out the DC current. Connected in the line from
the bridge 102 to the smoke detector is a 1/2W resistor 100 to
current limit the voltage. Connected between power line 107
and the smoke detector 42 is a zenor diode 96 which acts as a
voltage regulator providing 9 volts. There are two identical
diodes indicated at 109 which act to rectify the square wave
signal from the smoke detector in order to charge a capacitor
94. The purpose of the capacitor 94 is to provide a delay so
2119194
i~ .
- 15
that two beeps from the smoke detector are required to shut
down the furnace. As is usual, the smoke detector 42 is
provided with a test switch indicated at 92, which switch can
be closed manually in order to test the unit.
Indicated at 46 is a latching relay, which relay is
located in the housing 22 containing the smoke detector. This
latching relay is activated once the smoke detector has
detected smoke and has set off an alarm and will continue to
operate to keep the furnace off even if the electrical power
fails. An electrical line 108 connects this latching relay to
the smoke detector and the capacitor 94. The relay has two
contacts indicated at 112 and 114. These contacts are shown
in the reset condition and in the reset condition power is
supplied to a second relay indicated at 118. This second relay
must be energized in order to allow the furnace to operate.
However, in the set condition the upper contact 114 will
supply 12 volt power to the remote beeper or alarm device 76
while the lower contact 112 supplies 12 volt power to a LED
diode 115. Also, in the set condition the upper contact
disconnects power from the second relay 118. The second relay
has a single contact 120 and this relay is connected to a
terminal strip with two connecting screws indicated at 121.
It is the screws 121 which are connected to the furnace wires
including electrical lead 82 indicated in Figure 1. Also
shown in Figure 5 is a lK resistor 116. The resistor 116
which is connected to ground is a current limiting resistor
for the alarm LED 115, this LED comprising a simple red light
- 211919~
- 16
indicating that the alarm has been triggered and is shutting
down the furnace.
In one preferred embodiment the zenor diode 96 is type
IN5346B and the two diodes 109 are type IN4001.
It will be understood that the reset button at 104 is
pushed to close the switch when smoke has been cleared from
the system and one wishes the furnace now to operate.
It will be appreciated that various modifications and
changes can be made to the described combined smoke detection
and furnace shut-off apparatus without departing from the
spirit and scope of this invention. Accordingly, all such
modifications and changes as fall within the scope of the
appended claims are intended to be part of this invention.
