Heat saving device for space heating furnace

An improvement in space heating furnaces fueled by gas or liquid for saving heat ordinarily lost through the draft system of such a furnace, comprises a means of automatically closing the air inlet to the combustion chamber as well as the air inlet to the diverter air opening at the flue immediately after cessation of the main burner flame, and also for opening both of the air inlets immediately prior to the ignition of the main burners.

BACKGROUND OF THE INVENTION 
Field: The invention is in the field of gas or liquid fueled space heating 
furnaces which draw combustion air from the inside of the buildings which 
they heat or from a separate fresh air supply connected to an external 
source and exhaust the combustion gases exteriorly of the buildings. 
State of the Art: Furnaces fueled by various kinds of gases such as natural 
gas, methane, propane, etc., or liquids, such as fuel oil, are customarily 
used for space heating of buildings and other enclosures of various kinds. 
Hot air furnaces fueled by natural gas are widely used for heating the 
interior of homes. Such space heating furnaces have been constructed in 
many different ways, but in all cases, they require a fresh air supply, 
wherein the fresh air is either drawn from the interior of the building 
or, in some special cases, from a separate connection which conducts the 
fresh air directly from the exterior of the building into the furnace 
area. Combustion gases are exhausted from the combustion chamber to a flue 
which conducts the gas by way of a stack or chimney to the atmosphere 
exteriorly of the building. To provide proper draft in the flue, air from 
the fresh air supply is drawn into the flue through a diverter air opening 
therein. 
A significant waste of energy results during periods when the furnace is 
not operating, i.e., when fuel is not being burned in the furnace, as a 
result of: 
A. Heat loss due to warm air escaping to the exterior of the building 
through the air inlet to the combustion chamber and the air drawn into the 
flue through the diverter air opening in the flue. 
B. Unnecessary cooling of the furnace heat exchanger which is caused by 
heat transfer from the previously heated surfaces of the heat exchanger to 
the air being exhausted to the exterior of the building via the flue. 
To alleviate these heat losses, it has been suggested that dampers be 
installed in the exhaust flues of such furnaces, and it is a common 
expedient to utilize such dampers in coal-burning furnaces and fireplaces. 
However, similar dampers in modern automatically controlled gas and liquid 
fueled furnaces have been considered to be highly dangerous. An extreme 
hazard exists if the burner of the furnace to which such a damper is 
attached comes on without the damper opening the vent or flue. 
Objective: The objective of this invention was to develop a reliable, safe 
mechanism by which gas flow through the draft system of the furnace is 
automatically closed when the burner is not operating and opened when it 
is operating. 
SUMMARY OF THE INVENTION 
In accordance with the invention, the foregoing objective is achieved by 
providing an improvement in the draft systems of space heating furnaces 
which burn gas or liquid fuels and are commonly used to heat homes and 
other buildings. Such draft systems comprise a combustion air inlet and 
passages which allow air to be drawn into the combustion chamber from the 
inside of the building being heated or from fresh air conducted directly 
from the exterior of the building. A flue conducts exhaust gases to a 
stack or chimney which vents the combustion gases to the exterior of the 
building being heated. A diverter air inlet and passages for conducting 
air to the flue are usually provided, so that air from the inside of the 
building or from air obtained directly from the exterior of the building 
can be drawn into the flue to provide a proper draft. 
The improvement of the present invention comprises the provision of means 
for automatically closing and opening the combustion air inlet and the 
diverter air inlet of the draft system in response to preset conditions 
occurring in the operation of the furnace. The combustion air inlet and 
the diverter air inlet are closed when fuel is not being burned, and 
opened immediately prior to ignition of the burners and during the period 
when fuel is being burned. Thus, during intermittent periods when the 
furnace is not in operation, i.e., when fuel is not being fed to the 
burner of the furnace and heat is not being produced, the combustion air 
inlet and the diverter air inlet are closed, thereby preventing loss of 
heated air from the inside of the building through the draft system of the 
furnace, or loss of heat due to the premature cooling of the heat 
exchanger in the furnace caused by the flow of the cooler interior 
building air or the flow of the cold air being drawn from the fresh air 
which is drawn from the exterior of the building in those instances where 
the fresh air supply to the furnace is air drawn from the exterior of the 
building. When the furnace comes on, i.e., when fuel is to be fed to the 
burner and be burned in the combustion chamber, the combustion air inlet 
opens and allows the normal supply of combustion air to flow into the 
combustion chamber, and the diverter air inlet opens so that air can be 
drawn into the flue to establish a proper draft. 
In a preferred embodiment of the invention, a shutter means is provided 
over the combustion air inlet and similarly over the diverter air inlet, 
with means for automatically opening and closing the shutter means when 
the furnace is operating and when it is on standby between periods of 
operation, respectively. The shutter means is preferably spring biased to 
hold it in the closed position, and a motor drive is provided to 
counteract the spring bias and thereby open the shutter against the force 
of such spring bias when the motor drive is energized. Means are provided 
for energizing the motor drive during those periods when the furnace is 
operating, i.e., when fuel is being burned in the combustion chamber. When 
the furnace shuts down to its standby condition, the motor drive is 
de-energized and the shutter closes under the force of the spring. 
The operation of the motor drive is advantageously controlled by the 
thermostat, which is commonly employed on furnaces of the type concerned 
herewith to control the automatic fuel control valve and thereby the flow 
of fuel to the combustion chamber of the furnace. When the thermostat 
indicates a need for heat, it energizes a relay which in turn energizes 
the motor drive causing the shutter to open, thereby permitting air to 
flow through the combustion air inlet to the combustion chamber and 
through the diverter air inlet to the flue. When the shutter reaches the 
"full open" position, a switch is tripped, closing the circuit which 
activates the fuel control valve, thus introducing the fuel into the 
combustion chamber for ignition. The shutter remains open as long as the 
thermostat indicates a need for heat and, therefore, as long as fuel is 
being burned in the furnace. As soon as the heat requirement has been 
satisfied, the thermostat de-energizes the relay which de-energizes the 
drive motor causing the shutter to close under the spring force. The 
closing action of the shutter releases the switch which de-energizes the 
fuel control valve, thus stopping the flow of fuel into the combustion 
chamber, thereby eliminating the need for air flow to the combustion 
chamber or to the diverter air inlet.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
A furnace having original equipment conforming to the invention is 
illustrated in FIGS. 1-3. The furnace comprises a housing having return 
air inlet 10 in one of the sides 11 thereof. The return air circulates 
through a conventional heat exchange plenum in the furnace, and heated air 
flows from the hot air outlet 12 on the top 13 of the furnace. 
A gas or liquid fuel is burned at burner 14 within the combustion chamber 
15 of the furnace. Ignition means are provided as part of the burner for 
igniting the fuel when fuel is fed to the burner. The ignition means 
commonly comprises a pilot flame which burns continuously. The draft 
system of the furnace provides for proper flow of combustion air into the 
combustion chamber 15 of the furnace to support combustion of the fuel. 
As shown in FIGS. 1-3, the front 16 of the furnace is provided with two air 
openings 17 and 18, respectively. The upper or diverter air opening 17 
provides for air flow to chamber 19 wherein hot exhaust gases from the 
outlet 20 of the combustion chamber 15 mix with the air from opening 17, 
and the mixture of gases are then exhausted through flue 21 at the top of 
the furnace. The introduction of air through opening 17 to chamber 19 
prevents an excessive draft from being pulled through the combustion 
chamber 15 of the furnace. The operation and design of chamber 19 per se 
is well known in the art and does not form a part of the present 
invention. 
The lower or combustion air opening 18 opens to a combustion air supply 
chamber 22 from which the combustion air is drawn into the combustion 
chamber 15. As is common in such furnaces, chamber 19 and the combustion 
air supply chamber 22 are separated by a partition 23 which provides a 
small opening 24 for flow communication therebetween. The small opening 
24, as is well known in the art, prevents excessive pressure differentials 
from developing between chamber 19 and the combustion air supply chamber 
22. 
In accordance with this invention, two shutter plates 25 and 26 (FIGS. 2 
and 3) are adapted to open and close the openings 17 and 18, respectively. 
The shutter plates 25 and 26 are pivotally connected along their lower 
edge to the front 16 of the furnace so that each of the shutter plates can 
be rotated back and forth between an essentially upright position as shown 
in FIG. 2, wherein the openings 17 and 18 are closed, and an essentially 
laterally extending position as shown in FIG. 3, wherein the openings 17 
and 18 are open. 
A linkage arm 27 is connected between the shutter plates 25 and 26 so that 
as the upper end of the arm 27 is pushed downwardly, the shutter plates 25 
and 26 are simultaneously moved into their upright position closing the 
openings 17 and 18. Conversely, as the upper end of the linkage arm 27 is 
pulled upwardly, the shutter plates 25 and 26 are simultaneously moved 
into their laterally extending position, thereby opening the openings 17 
and 18. 
The upper end of the linkage arm 27 is connected to a motor drive unit 28 
by a knee action linkage system 29. A spring 30 is provided which urges 
the knee action linkage system 29 to assume an extended position as shown 
in FIG. 2. In the extended position, the upper end of arm 27 is pushed 
downwardly, thereby closing the shutter plates 25 and 26 over the openings 
17 and 18, respectively. When the motor drive unit 28 is activated, it 
moves the knee action linkage system against the force of spring 30 into 
an angled, drawn-up position as shown in FIG. 3. In this position, the 
upper end of arm 27 is pulled upwardly, and the shutter plates 25 and 26 
are simultaneously moved into their laterally extending positions, thereby 
opening openings 17 and 18, respectively. 
A conventionally constructed furnace which has been modified to conform to 
the present invention is shown in FIG. 4. This furnace is similar in its 
construction to the furnace shown in FIGS. 1 and 3, with the exception 
that the shutter plates 25 and 27 and system for opening and closing the 
air inlets 17 and 18, as built into the furnace of FIGS. 1-3, are not part 
of the original equipment of the furnace shown in FIG. 4. The furnace 
shown in FIG. 4 has a fuel burning and combustion gas exhausting system 
similar to that of the furnace shown in FIGS. 1-3. Combustion air is drawn 
through an opening in the front 16 of the furnace, and the combustion 
gases are exhausted through flue 21. As in the furnace of FIGS. 1-3, a 
second opening in the front of the furnace is provided communicating with 
a chamber similar to chamber 19 shown in FIG. 2. Air drawn through the 
second opening mixes with the hot exhaust gases coming from the combustion 
chamber in the same manner as hereinbefore described with respect to the 
furnace shown in FIGS. 1-3. 
A shutter box 31 is attached to the front 16 of the furnace as shown in 
FIG. 4 to cover the openings in the furnace which communicate with 
respective chambers therein corresponding to chambers 15 and 19 as shown 
in the furnace illustrated in FIGS. 1-3. A set of shutter plates 32 are 
positioned in the shutter box 31, with the plates 32 being attached to a 
linkage arm 33, which when pushed upwardly simultaneously closes the 
shutter plates 32 and when pushed downwardly simultaneously opens the 
shutter plates 32. A motor drive unit 34, attached to the shutter box 31 
and linkage arm 33, is adapted to push the linkage arm 33 downwardly to 
simultaneously open the shutter plates 32. The linkage arm 33 is biased by 
spring means which apply a constant force thereon in an upward direction. 
When the motor drive unit 34 is energized, it pushes the linkage arm 33 
downwardly against the force of the spring means, thereby simultaneously 
opening the shutter plates 32. When the motor drive unit 34 is 
de-energized, the spring means forces the linkage arm 33 to move in the 
opposite direction, thereby simultaneously closing the shutter plates 32. 
The shutter plates 25 and 26 of the embodiment illustrated in FIGS. 1-3 and 
the shutter plates 32 of the embodiment illustrated in FIG. 4 are adapted 
to automatically open and close in response to preset conditions occurring 
in the operation of the furnace. The operation of the shutters and the 
furnace will be further explained with reference to electrical diagram of 
the furnace control system shown in FIG. 5. 
The burning of fuel in the furnace is controlled primarily by the 
thermostat 35, as is conventional in such furnaces. The thermostat 35 is 
connected in series with one pole of the secondary winding of a 
transformer 36, a relay 37, and then to the other pole of the transformer 
36. When the thermostat 35 makes contact, it energizes relay 37. In 
conventional furnaces, the relay 37 would in turn energize the automatic 
fuel control valve 38 thereby turning the furnace on. 
In accordance with the present invention, the thermostat 35 does not 
control the automatic fuel control valve 38 of the furnace directly, but, 
instead, energizes the relay 37, thereby closing the two contacts 37a and 
37b of the relay 37. Contact 37a is connected to the 120 volt supply to 
transformer 36, and when it is closed, the shutter motor 39 is energized. 
The motor 39 of FIG. 5 corresponds to the motor drive units 28 and 34 of 
FIGS. 1-3 and FIG. 4, respectively. The energization of the shutter motor 
results in the opening of shutters 25 and 26 of FIGS. 1-3 and of shutter 
plates 32 of FIG. 4. 
Contact 37b of relay 37 is connected with the automatic fuel control valve 
38 through a series connection with a switch 40, which is, in turn, 
associated with the shutter plates. Switch 40 is closed when the shutter 
plates are in their full open position. The contact 37b of relay 37 having 
been closed, the circuit to the automatic fuel control valve 38 is 
completed when the switch 40 is closed, and the furnace turns on. It 
should be noted, however, that the furnace can not be turned on, i.e., 
fuel ignited therein, unless the shutter plates are in their fully open 
position. If they are not in the fully open position, the switch 40 will 
remain open, and the automatic fuel control valve 38 will not be 
activated. 
A safety control unit 41 is associated with the automatic fuel control 
valve 38, as in conventional furnaces of the type illustrated. The safety 
control unit 41 serves as an override control of the automatic gas control 
valve, closing the valve in cases of pilot light malfunction or 
overheating of the heat exchange plenum in the furnace. The unit 41 
performs such functions independent of the improved draft system of this 
invention. A fan control 42 is also shown in FIG. 5 which controls the 
operation of the furnace fan motor 43. The operation of the fan control 
and the furnace fan is also independent of the present invention. The 
safety control unit 41, fan control 42, and fan motor 43 are shown simply 
as a part of the total electrical diagram of a typical furnace which 
otherwise conforms to the present invention. 
As long as the thermostat 35 indicates a need for heat and, therefore, as 
long as fuel is being burned in the furnace, the relay 37 remains 
energized and the shutter plates remain open, thereby allowing air to flow 
through the furnace draft system. As soon as the heat requirement has been 
satisfied, the thermostat 35 breaks its connection to the relay 37, which, 
in turn, de-energizes the motor 39 on the shutter drive unit, and the 
shutters close under the spring forces which are associated therewith. As 
the shutters initiate their closure, the switch 40 is disconnected, and 
the automatic fuel control valve 38 turns off so that fuel flow to the 
furnace ceases. Thus, when the furnace has been turned off, and it is in 
its standby condition, the shutters close the openings to the combustion 
chamber and flue of the furnace, thereby preventing heat loss due to warm 
air from the interior of the building escaping to the exterior through the 
flue and chimney of the furnace. In addition, unnecessary cooling of the 
furnace heat exchanger by air flowing from the building through the flue 
and chimney is also prevented. 
The draft control system of the present invention is safe, even in cases of 
malfunction of one or more of the component parts thereof. The shutter 
system must be in its fully open position for the furnace to ignite. Even 
if the switch 40 failed and remained in its closed position indefinitely 
and the motor 39 or some other component of the shutter system 
simultaneously failed so that ignition of the furnace could occur while 
the shutter system remains closed, there is no serious safety problem. The 
fuel introduced into the combustion chamber would burn with incomplete 
combustion due to the limited air which could be drawn into the combustion 
chamber of the furnace through the closed shutter system. The incomplete 
products of combustion would be exhausted to the exterior of the building 
through the flue and chimney so that they would not present a fume problem 
within the building. The heating efficiency of the furnace would drop 
significantly, thus calling attention to the inhabitants of the building 
that some malfunction had occurred in the furnace, and the malfunction 
would then be corrected. 
In systems which have been proposed heretobefore of placing a damper in the 
flue or chimney of the furnace, a severely hazardous situation exists if 
the damper does not open. In such situations, the combustion gases are 
released to the inside of the building being heated, and thus, present an 
air contamination or fume problem along with a fire hazard. In accordance 
with the present invention both of these problems, and at least about a 20 
percent reduction in fuel consumption is obtained as compared to 
conventional furnaces which do not conform to the present invention. 
Whereas this invention is here illustrated and described with specific 
reference to embodiments thereof presently contemplated as the best mode 
of carrying out such invention in actual practice, is to be understood 
that various changes may be made in adapting the invention to different 
embodiments without departing from the broader inventive concepts 
disclosed herein as comprehended by the claims that follow.