U.S. patent application number 09/777405 was filed with the patent office on 2002-02-07 for apparatus for and method of operating a furnace blower to evaporate condensate within an exhaust flue.
This patent application is currently assigned to Jakel Incorporated. Invention is credited to Gatley, William Stuart JR., Halgash, Linda M..
Application Number | 20020014233 09/777405 |
Document ID | / |
Family ID | 46277313 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014233 |
Kind Code |
A1 |
Gatley, William Stuart JR. ;
et al. |
February 7, 2002 |
Apparatus for and method of operating a furnace blower to evaporate
condensate within an exhaust flue
Abstract
A blower for a furnace is provided where the blower has an
impeller that is configured to create a primary air flow of
combustion air into the blower housing and a secondary air flow of
cooling air through the blower motor. The primary air flow of
combustion air into the furnace generates hot exhaust gases for a
heat exchanger in the furnace. The secondary air flow cools the
blower motor. The secondary air flow is mixed with the hot exhaust
gases in the blower housing and cools the exhaust gases before
being discharged from the blower housing. A control operates the
blower for a time period after each combustion cycle to introduce
ambient air into the exhaust flue and chimney to ensure the
evaporation of any condensate forming from the products of
combustion contained in the exhaust. The blower may be a variable
or multi-speed motor so that a different motor speed may be used
for combustion than for the run time after combustion.
Inventors: |
Gatley, William Stuart JR.;
(Cassville, MO) ; Halgash, Linda M.;
(Edwardsville, IL) |
Correspondence
Address: |
R. Haferkamp
HOWELL & HAFERKAMP, L.C.
Suite 1400
7733 Forsyth Boulevard
St. Louis
MO
63105
US
|
Assignee: |
Jakel Incorporated
|
Family ID: |
46277313 |
Appl. No.: |
09/777405 |
Filed: |
February 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09777405 |
Feb 6, 2001 |
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09631319 |
Aug 3, 2000 |
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6318358 |
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Current U.S.
Class: |
126/110R ;
126/99R |
Current CPC
Class: |
F23L 17/005 20130101;
F24H 3/065 20130101; F04D 29/5806 20130101; F04D 25/082
20130101 |
Class at
Publication: |
126/110.00R ;
126/99.00R |
International
Class: |
F24H 003/00 |
Claims
What is claimed is:
1. A method for drying the condensate from an exhaust flue for a
fuel burning appliance, said fuel burning appliance having a
combustion blower to exhaust the products of combustion from a
combustion chamber into the exhaust flue, the method comprising the
step of running the combustion blower after the end of a combustion
cycle for a time at least longer than a post purge time period but
less than continuously.
2. The method of claim 1 wherein the running step includes the step
of running the combustion blower for at least approximately three
minutes after the end of a combustion cycle.
3. The method of claim 2 further comprising the step of running the
combustion blower after the end of each combustion cycle for the
same time period.
4. The method of claim 3 wherein the exhaust blower includes an
electric motor and further comprising the step of drawing in some
ambient air through the electric motor.
5. The method of claim 3 wherein the fuel burning appliance further
comprises a control, and further comprising the step of setting the
control to run the combustion blower for at least three minutes
after the end of a combustion cycle.
6. The method of claim 5 further comprising the step of running the
exhaust blower at a different speed after the end of a combustion
cycle.
7. The method of claim 6 wherein the motor is a variable speed
motor and the step of running the exhaust blower at a different
speed comprises the step of changing the speed at which the
variable speed motor runs.
8. The method of claim 6 wherein the motor is a multi-speed motor
and the step of running the exhaust blower at a different speed
comprises the step of changing the speed at which the multi-speed
motor runs.
9. The method of claim 2 wherein the fuel burning appliance further
comprises a control, and further comprising the step of setting the
control to run the combustion blower for at least three minutes
after the end of each combustion cycle.
10. The method of claim 9 further comprising the step of running
the exhaust blower at a different speed after the end of a
combustion cycle.
11. The method of claim 10 wherein the motor is a variable speed
motor and the step of running the exhaust blower at a different
speed comprises the step of changing the speed at which the
variable speed motor runs.
12. The method of claim 10 wherein the motor is a multi-speed motor
and the step of running the exhaust blower at a different speed
comprises the step of changing the speed at which the multi-speed
motor runs.
13. A fuel burning appliance having an exhaust outlet adapted for
connection to an exhaust flue, an exhaust blower for exhausting
products of combustion through said exhaust outlet, and a control
for controlling the operation of the exhaust blower, the control
being configured to run the exhaust blower after the end of a
combustion cycle for a time at least longer than a post purge time
period but less than continuously to thereby ensure that the
exhaust flue dries of condensate formed therein by said products of
combustion.
14. The fuel burning appliance of claim 13 wherein said control is
configured to run the exhaust blower after the end of a combustion
cycle for at least approximately three minutes but less than
continuously.
15. The fuel burning appliance of claim 14 wherein said exhaust
blower has an electric motor, and further comprising a connection
between said motor and a blower housing through which ambient air
is drawn as the exhaust blower is operated.
16. The fuel burning appliance of claim 14 wherein said electric
motor comprises a variable speed motor and said control is
configured to run said electric motor at a different speed during a
combustion cycle than after a combustion cycle.
17. The fuel burning appliance of claim 14 wherein said electric
motor comprises a multispeed motor and said control is configured
to run said electric motor at a different speed during a combustion
cycle than after a combustion cycle.
18. The fuel burning appliance of claim 13 wherein said control is
configured to permit the exhaust blower post combustion cycle run
time to be adjusted.
19. A fuel burning appliance having an exhaust outlet adapted for
connection to an exhaust flue, an exhaust blower for exhausting
products of combustion through said exhaust outlet, and a control
for controlling the operation of the exhaust blower, the control
being configured to run the exhaust blower after the end of each
combustion cycle for at least about three minutes to thereby ensure
that the exhaust flue dries of condensate formed therein by said
products of combustion.
20. The fuel burning appliance of claim 19 wherein said exhaust
blower has an electric motor, and further comprising a connection
between said motor and a blower housing through which ambient air
is drawn as the exhaust blower is operated.
21. The fuel burning appliance of claim 20 wherein said electric
motor comprises a variable speed motor and said control is
configured to run said electric motor at a different speed during a
combustion cycle than after a combustion cycle.
22. The fuel burning appliance of claim 20 wherein said electric
motor comprises a multi-speed motor and said control is configured
to run said electric motor at a different speed during a combustion
cycle than after a combustion cycle.
23. A method for drying the condensate from an exhaust flue for a
fuel burning appliance, said fuel burning appliance having a
combustion blower to exhaust the products of combustion from a
combustion chamber into the exhaust flue, the method comprising the
step of running the combustion blower after the end of a combustion
cycle for at least about three minutes but less than
continuously.
24. The method of claim 23 further comprising the step of drawing
at least some ambient air into the exhaust blower at least during
the time period after the end of the combustion cycle.
25. The method of claim 24 wherein the exhaust blower includes an
electric motor and wherein the step of drawing in some ambient air
includes the step of drawing in some ambient air through the
electric motor.
26. The method of claim 25 wherein the fuel burning appliance
further comprises a control, and further comprising the step of
setting the control to run the combustion blower for at least three
minutes after the end of a combustion cycle.
27. The method of claim 26 further comprising the step of running
the exhaust blower at a different speed after the end of a
combustion cycle.
28. A method for drying the condensate from an exhaust flue for a
fuel burning appliance, said fuel burning appliance having a
combustion blower to exhaust the products of combustion from a
combustion chamber into the exhaust flue, the method comprising the
step of running the combustion blower after the end of each
combustion cycle for a fixed period of time equal to at least three
minutes but less than continuously.
29. The method of claim 28 wherein the exhaust blower includes an
electric motor and further comprising the step of drawing in some
ambient air through the electric motor.
30. The method of claim 29 wherein the fuel burning appliance
further comprises a control, and further comprising the step of
setting the control to run the combustion blower for at least three
minutes after the end of each combustion cycle.
31. The method of claim 30 further comprising the step of running
the exhaust blower at a different speed after the end of each
combustion cycle.
32. A method for drying the condensate from an exhaust flue for a
fuel burning appliance, said fuel burning appliance having a
combustion blower to exhaust the products of combustion from a
combustion chamber into the exhaust flue and a control configured
to control the operation of said blower, the method comprising the
step of determining a duty cycle for said combustion blower to
thereby ensure that the exhaust flue dries of condensate formed
therein by said products of combustion.
33. The method of claim 32 wherein the determining step includes
the step of determining either of the frequency or duration of
blower run time after appliance combustion cycles.
34. The method of claim 33 wherein the control is configured to
perform the determining step.
35. The method of claim 34 wherein the determining step includes
the step of determining blower run time after combustion.
36. The method of claim 34 wherein the determining step includes
the step of determining a frequency for blower run time after
combustion.
37. The method of claim 32 wherein the step of determining said
blower duty cycle includes determining blower run time after
combustion to be a time greater than a post purge time period but
less than continuously.
38. The method of claim 32 wherein the step of determining includes
the step of determining the duty cycle for the exhaust blower in
response to the appliance duty cycle.
39. A fuel burning appliance having an exhaust outlet adapted for
connection to an exhaust flue, an exhaust blower for exhausting
products of combustion through said exhaust outlet, and a control
for controlling the operation of the exhaust blower, the control
being configured to determine a duty cycle for the exhaust blower
to thereby ensure that the exhaust flue dries of condensate formed
therein by said products of combustion.
40. The fuel burning appliance of claim 39 wherein said control is
configured to determine a post combustion blower run time greater
than a post purge time period but less than continuously.
41. The fuel burning appliance of claim 39 wherein said control is
configured to determine a frequency for blower run time after
combustion.
42. The fuel burning appliance of claim 39 wherein said control is
configured to determine the duty cycle for the exhaust blower in
response to the appliance duty cycle.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. Ser. No.
09/1631,319 filed Aug. 3, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to a draft inducing blower
in a furnace, and, more particularly, the invention pertains to an
improvement in the blower design that provides not only for
internal cooling for a motor that drives the blower but also a
control that runs the blower motor for a period of time after a
combustion cycle to ensure that any condensate that collects in the
exhaust flue including the chimney will evaporate.
[0004] 2. Description of the related Art
[0005] Blowers to which the present invention is directed are
common in the art. Generally, these blowers are located downstream
of a combustion chamber or combustion tubes in the furnace,
depending upon the style of furnace. The blower induces combustion
air to be drawn into the combustion chamber or combustion tubes,
where the combustion air is mixed with fuel and ignited to generate
heat for the furnace. The heated exhaust gases are then drawn
through a heat exchanger by the blower and discharged from the
blower to an exhaust pipe or flue that vents to the outside
atmosphere typically through a chimney. This chimney may be a
masonry chimney with a clay tile liner, as is well known in the
art.
[0006] The blower generally includes a blower housing and a blower
motor installed on the blower housing. The blower housing typically
has a side wall, top piece, and bottom piece that define a volute
for the blower housing. When the blower is energized, an impeller,
operably connected to a shaft of the blower motor, rotates in the
volute to draw exhaust gases through an intake hole in the center
of the bottom piece and to compress gases in the volute. The
impeller draws exhaust gases directly from the combustion chamber
or combustion tubes into the blower housing. The pressurized
exhaust gases are directed into a discharge exit that extends
outward and away from the side wall of the blower housing. In this
arrangement, the impeller rotates at a high rate of speed to
generate sufficient air flow to draw combustion air into the
combustion chamber and combustion tubes and to expel the exhaust
gases into the exhaust flue. The discharge exit is coupled to an
exhaust pipe or flue that vents the exhaust gases to atmosphere
through a chimney. This exhaust flue is totally dependent on the
installation, but is subject to certain limitations imposed by
various building codes such as the National Fuel Gas Code and in
accordance with the safety standards set by various industry
groups.
[0007] In a typical conventional furnace, the combustion air is
drawn into a vestibule of the furnace before it is directed into
the combustion chamber or combustion tubes. Generally, the blower
motor and blower housing are located in the vestibule with the
blower intake in communication with the combustion chamber or
combustion tubes. Control electronics for the furnace are also
generally located in the vestibule or blower compartment.
[0008] During operation of the furnace, temperatures in the
vestibule increase and tend to degrade performance of furnace
components located in the vestibule. The proximity of the vestibule
to the combustion chamber or tubes and the heat generated by the
blower motor as the motor runs elevate the temperature within the
vestibule. The hot exhaust gases circulating through the blower
also contribute to the elevated temperatures in the vestibule. The
elevated temperature within the vestibule tends to shorten the life
of the blower motor, and electronics and controls located within
the vestibule. However, because the blower draws relatively cool
air into the vestibule before combustion, the vestibule is
generally the preferred place on the conventional furnace for
positioning temperature sensitive equipment for the furnace.
Additionally, to maintain proper operation of the blower motor
during the period of elevated temperature in the vestibule,
conventional blower motors utilize an auxiliary fan attached to the
rotating shaft of the motor to dissipate the heat generated by the
motor.
[0009] Although the auxiliary fan usually provides adequate heat
removal for the motor, the auxiliary fan has many disadvantages.
First, the use of an auxiliary fan on the blower motor increases
the size and/or height of the motor assembly, thereby preventing
the streamlining of the motor assembly and reduction of the space
reserved for the blower in the furnace. Because the auxiliary fan
is generally positioned outside of the motor casing, guards and
other safety devices must be attached to the motor casing to
prevent inadvertent contact with the rotating fan blades during
operation. The guard and the fan itself also add cost to the blower
motor. The blower motor with an auxiliary fan generates additional
noise. Finally, because the motor is positioned in the vestibule,
the auxiliary fan re-circulates and reuses air in the vestibule.
This re-circulation and reuse of the air in the vestibule
contributes to the elevated temperatures of the vestibule and the
associated components positioned therein. Because the motor
operates in the vestibule at higher temperatures, the motor
capacity must again be increased, which adds cost to the
blower.
[0010] Historically, gas fired furnaces came first in which no
combustion blower was provided and instead the natural convection
forces were relied on to exhaust the products of combustion from
the combustion chamber and heat exchanger. In these kind of
installations, measurements were made and standards were set for
the sizing and placement of flue vents to ensure that condensate
which had a tendency to form on the inside of chimneys was allowed
to evaporate to avoid damaging the chimney liner typically made of
clay tile. About twenty years or so ago, combustion blowers were
first implemented as they were found to increase the efficiency of
furnaces in converting fuel into usable heat. While this
improvement was highly desirable from an efficiency standpoint, it
created new problems with respect to determining and implementing
the proper size of flue pipes needed to ensure that the chimney
remained dry as the furnace operated. These issues were worked out
with the solutions being that, in general, smaller diameter chimney
or vents were required to accommodate the exhaust from a furnace of
the same capacity having a combustion blower than a simple draft
furnace.
[0011] As a partial solution to this problem, which was
particularly acute for replacement of old design draft type
furnaces not having draft induced motors with draft induced
furnaces which might otherwise require expensive adjustment of flue
pipe sizes or furnace placement, what are called chimney kits were
developed. Examples of a chimney kit may be found in U.S. Pat. Nos.
6,112,741; 5,941,230; and Des. 386,577; the disclosures of which
are incorporated herein by reference. Basically, these chimney kits
comprise draft hoods that, through convection, introduce ambient
air into the exhaust flue which helps to lower the dew point
temperature in the flue which thereby increases the tendency for
condensate to form in the chimney after which it can be evaporated.
Regulating the air flow through the chimney kit allows the room
temperature air to flow through the kit. This allows a natural
draft to occur as in the older style furnaces. While a chimney kit
does provide a solution enabling replacement of an older design
draft furnace with an updated furnace having a combustion blower
with minimal reconfiguring of the flue pipes, it does have several
drawbacks including its expense and installation cost.
[0012] Draft hoods have also found use in other fuel fired
appliances such as gas hot water heaters. However, these
installations have to deal with the same "wet" chimney concerns,
and retrofit installations, or replacement installations, must also
find a way to prevent a wet chimney. This is true for any Category
I or III fuel burning appliance as defined by the appropriate
standards agency, and includes various types of appliances
including water heaters, furnaces, etc. fueled by various types of
fuel including oil, gas, wood, etc. A report and paper was prepared
in August of 1992 by Battelle for the Gas Research Institute
entitled "Analysis of the Effects of Dilution Air and Appliance
Efficiency on Venting Category I Gas Appliances", the disclosure of
which is incorporated herein, which investigated the impact of
dilution air and appliance efficiency on the design and
installation guidelines for venting Category I gas appliances. The
investigation utilized a computer program named "VENT II" for
simulating appliance operation given a specified set of
installation parameters to help determine whether a chimney of a
preselected size would reach a steady state "dry" condition within
an allowed period of operation with a draft hood. Several
conclusions drawn in the study are important for consideration
here. It was concluded that a draft hood did not appear to offer
any advantages on an appliance with a steady state efficiency
greater than 80.5 percent in terms of the venting requirements, but
"may" offer significant advantages for appliances operating at 80.5
percent efficiency and below. Indeed it was concluded "At 83
percent steady-steady efficiency, no method of adding dilution air
to the vent configuration examined (20-ft. height, 5-ft.single-wall
lateral, 4-inch diameter) allowed the chimney to dry out within the
wet-time limit." These conclusions were summarized in Table 4 in
the report which indicated that even under the operational
conditions of the several modalities tried, an appliance operating
at 83 percent efficiency always resulted in a wet chimney. These
various operating modalities included a) no dilution air introduced
into the flue; b) use of a draft hood to introduce dilution air; c)
use of a draft hood and a flue damper which allowed dilution air to
enter the vent system only during the on-cycle; d) a small hole in
the blower housing through which dilution air could pass
continuously; and e) continuous operation of the combustion blower.
For an appliance operating at 80.5 percent efficiency only the
draft hood modality achieved a dry chimney. Thus, based on this
authoritative report, a draft hood was taught as the modality of
choice in order to achieve a dry chimney, over the other modalities
tested including running the blower full time.
[0013] It is also known in the prior art that it is desired to
operate the combustion blower for perhaps a pre-purge time and a
post-purge time, to clear the combustion chamber both before and
after combustion. The time typically chosen by a furnace
manufacturer for post-purge cycles is on the order of 15 to 30
seconds, and as best known to the inventors herein less than 1
minute in virtually all cases. This time is typically set in the
furnace control at the factory, is thus typically independent of
the installation, and is included in draft hood equipped fiurnaces
indicating that this setting is not seen as having any impact on
the condensate issue.
[0014] Therefore, it is an object of the present invention to
combine the advantages of an improved blower that overcomes the
disadvantages of conventional blowers, including providing a blower
that cools the blower motor without the use of an auxiliary fan
attached to the blower motor, while at the same time minimizing the
condensate formation problem that limits the replacement of old
design draft furnaces without the need of a metal vent liner. Still
another object of the invention is to eliminate the need for a
draft hood or chimney kit for a draft induced furnace and yet still
achieve a dry chimney, especially in a replacement installation for
a simple draft induced furnace.
SUMMARY OF THE INVENTION
[0015] The present invention overcomes shortcomings of prior art
draft induced furnaces that use an auxiliary fan attached to the
blower motor to cool the blower motor but which at the same time
require the use of a chimney kit or metal vent liner for
replacement installations. The blower of the present invention
provides cooling for the blower motor with a flow of air induced by
the same combustion blower motor and which also incorporates a
control that provides a method of operation that achieves a dry
chimney in replacement installations of old design draft furnaces.
The present invention may also be used with conventional draft
induced furnaces that have a combustion blower, without the
inventive blower motor cooling feature, to permit them to be
retrofit into existing installations as well.
[0016] The blower of the present invention has an impeller that is
configured to create a primary air flow of combustion air into the
blower housing and a secondary air flow through the blower motor.
The secondary air flow is drawn through a casing of the blower
motor and into the blower housing where it is mixed with the
exhaust gases and discharged from the blower housing. Preferably,
the blower housing has an enlarged shaft hole that is sized to
allow sufficient cooling air to pass through the motor casing and
motor into the blower housing.
[0017] During furnace operation, the impeller of the blower draws
air into the vestibule. A first portion of the air is used by the
furnace for combustion, and a smaller, second portion of the air is
used for cooling the blower motor and exhaust gases. The impeller
draws the second portion directly over the motor including its
windings into the exhaust stream. Because the second portion is not
recirculated with air in the vestibule, it does not contribute to
the elevated temperature in the vestibule. As the air in the
vestibule has not been recycled by the blower motor, the air in the
vestibule is turned over and replaced more rapidly making the
vestibule cooler.
[0018] The blower of the present invention eliminates the need for
an auxiliary fan and allows for the blower to be more compact and
streamlined. The blower of the present invention has no external
rotating equipment, and the safety concerns and costs incident with
the auxiliary rotating fan are obviated. The blower motor of the
present invention allows the use of a lower cost blower motor while
reducing the noise associated with the blower. When installed in
the furnace, the blower of the present invention provides a cooler
vestibule and therefore cooler environment for the furnace
electronic controls. The blower of the present invention also cools
the exhaust stream from the furnace so as to lower overall
operating temperatures of the furnace.
[0019] Included with the present invention is an appliance control,
in the preferred embodiment a furnace control, that may be set to
allow for a running of the blower motor for a pre-selected time
after each combustion cycle to continue to provide dilution air
into the vent and chimney to dry it out. Test data have been
obtained using the VENT II program indicating that perhaps as short
as a 3 minute run time would provide the desired effect for a
typical installation for a 80.5 percent appliance. This provides
not only a simple and elegant solution to allow for the retrofit of
an appliance using a fan assisted combustion system (FACS) for an
older design and less efficient draft appliance, but at less cost
and greater effectiveness than with the draft hood solution of the
prior art.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0020] Further objectives and features of the present invention are
set forth in the following detailed description of the preferred
embodiment of the invention and in the drawing figures wherein:
[0021] FIG. 1 is a side elevation view of a blower of the present
invention;
[0022] FIG. 2 is a top plan view of the blower of FIG. 1;
[0023] FIG. 3 is a top plan view of the blower of FIG. 1 with a
blower motor removed from the blower;
[0024] FIG. 4 is a bottom view of the blower of FIG. 1;
[0025] FIG. 5 is a cross sectional view of the blower of FIG. 1
taken along the line 5-5 of FIG. 2;
[0026] FIG. 6 is a top cross section view of a blower housing of
the blower of FIG. 1 taken along the line 6-6 of FIG. 1;
[0027] FIG. 7 is a schematic drawing of a conventional low
efficiency furnace into which the blower of FIG. 1 is
installed;
[0028] FIG. 8 is a schematic drawing of a conventional high
efficiency furnace into which an alternative embodiment of the
blower present invention is installed; and
[0029] FIG. 9 is a schematic drawing of a alternate embodiment of
the low efficiency furnace of FIG. 7.
[0030] Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
[0031] FIGS. 1-6 provide details of the furnace blower 18 of the
present invention. The blower 18 is positioned on a blower mounting
surface 20 in a furnace 21 and includes a blower motor 22 and a
blower housing 24. The blower motor 22 is preferably positioned on
top of the blower housing 24 and contained within a motor casing
26. However, the motor 22 and blower housing 24 could have other
relative positions. The motor casing 26 is supported on a first
side wall 28 of the blower housing 24 by mounting feet 30 extending
outward from the motor casing 26. The mounting feet 30 preferably
have mounting holes 32, and mechanical fasteners 34 are directed
through the mounting holes 32 to secure the motor casing 26 to the
first side wall 28 of the blower housing 24.
[0032] As shown in FIG. 2, on a top side 36 of the motor 22
opposite the top, first side wall 28 of the blower housing 24, the
motor casing 26 preferably has at least one vent hole 38 through
the motor casing 26 that leads into an interior 40 of the motor
casing 26 surrounding the motor 22. Although several vent holes 38
are shown positioned on the top side 36 of the motor casing 26, the
vent holes may also be positioned along a top most edge of side
walls 42 of the motor casing 26. As shown in FIG. 5, the motor
casing 26 is also provided with a motor casing opening 44
preferably positioned adjacent the first side wall 36 of the blower
housing 24. A blower motor shaft 46 extends from the motor 22 in
the motor casing 26, through the motor casing opening 44 and into
the blower housing 24. The motor casing opening 44 and the vent
holes 38 have preferably the same cross sectional area and are
preferably positioned on the spaced apart portions of the motor
casing 26 to allow cooling air to flow through and cool as much of
the motor 22 as possible.
[0033] On the blower housing 24 opposite the first side wall 28 is
a bottom, second side wall 48 that rests adjacent the blower
mounting surface 20 in the furnace 21. An upstanding wall 52
extends between a first and second side walls 28,48, and together
the first and second side walls 28,48 and the upstanding wall 52
define a volute 54 of the blower housing 24. The blower housing 24
has a discharge exit 56 leading outward and away from the volute
54. The upstanding wall 52 and the bottom, second side wall 48 have
flange portions 58 extending parallel to the blower mounting
surface 20 with each of the flange portions 58 having a plurality
of matching holes 60. Mechanical fasteners 62 are preferably
threaded through the matching holes 60 into the blower mounting
surface 20 to secure the blower housing 24 to the furnace 21.
[0034] As shown in FIG. 3, the top, first side wall 28 is formed
with the upstanding wall 52 and has a shaft hole 64 that leads into
volute 54 of the blower housing 24. The shaft hole 64 is preferably
aligned with the motor casing opening 44 and receives the motor
shaft 46 therethrough. The shaft hole 64 and motor casing opening
44 can have the same cross sectional area so as to not restrict the
flow of cooling air from the interior 40 of the motor casing 26
into the blower housing 24.
[0035] As shown in FIG. 4, the bottom, second side wall 48 of the
blower housing is generally flat so that it may mount flush to the
blower mounting surface 20 of the furnace 21. The bottom, second
side wall 48 has a center intake 66 leading into the volute 54 of
the blower housing 24. The center intake 66 is preferably
positioned on the blower mounting surface 20 of the furnace 21 to
allow combustion exhaust gases to flow directly into the blower
housing 24. The center intake 66 preferably has the same cross
section area as the shaft hole 64 and motor casing opening 44 to
allow sufficient and balanced flow through the blower 18.
[0036] As shown in FIG. 5, the blower housing 24 has an impeller 70
rotatably disposed within the volute 54. The impeller 70 has a
circular back plate 72 and a first set of blades 74 on one side of
the circular back plate 72 and a second set of blades 76 on the
opposite side of the back plate 72. Preferably, the blades of the
first and second sets 74,76 are arranged in a circular pattern on
their respective sides of the back plate 72. The first set of
blades 74 is positioned adjacent the top, first side wall 28 of the
blower housing 24, and the second set of blades 76 is positioned
adjacent the bottom, second side wall 48. The blades 74,76 extend
axially away from the back plate 72 and a support ring 78 is
provided to hold a distal end 80 of each of the sets of blades
74,76 in a fixed perpendicular orientation to the backing plate 72.
In this arrangement, the first set of blades 74 is shorter in axial
length than the second set of blades 76 and therefore the first set
of blades 74 produces a lower flow rate than the second set of
blades 76. The impeller may also be provided with spiral vanes. In
this arrangement, the geometry of the vanes is dimensioned so that
the first set of vanes generates a lower flow rate than the second
set of vanes.
[0037] The impeller 70 is operably connected to the motor shaft 46
through a connection bushing 82 located on the circular back plate
72 of the impeller 70. Because the size of the first set of blades
74 is reduced, the connection bushing 82 is preferably positioned
on the underside of the circular back plate 72 in the center of the
second set of blades 76. In this arrangement, the motor shaft 46 is
directed through a center hole 84 in the circular back plate 70 and
into the connection bushing 82. A set screw 86 or a press-on
connection bushing 82 secures the impeller 70 to the motor shaft
46.
[0038] The backing plate 72 on the impeller 70 partitions the
impeller 70 into a first section 88 and a second section 90 that is
separated from the first section 88. The suction created by each of
the sections 88,90 is separately induced by the rotation and
orientation of the respective first and second sets of blades
74,76. When the impeller 70 is rotated by the blower motor 22, the
first set of blades 74 in the first section 88 create a suction at
the shaft hole 64 in the top side wall 28, and the second set of
blades 76 in the second section 90 create a suction at the intake
66 at the bottom side wall 48. Because the shaft hole 64 is aligned
with the motor casing opening 44, the first section 88 draws
cooling air through the interior 40 of the motor casing 26 into the
blower housing 24 while the second section 90 draws combustion
products into the blower housing 24. The impeller 70 compresses the
combustion products and cooling air together in the volute 54 and
directs the mixed exhaust gases to the discharge exit 56.
[0039] The operation of the blower 18 in the furnace 21 will be
discussed with reference to FIG. 7 to provide greater detail of the
flow paths generated by the blower 18 in the furnace 21. Although
the furnace 21 shown in FIG. 7 is a conventional low efficiency
furnace (e.g. 80%), a blower 18 of the present invention may also
be used in a high efficiency furnace (e.g. 90%) as shown in FIG. 8
with slight modifications to the blower housing to make it leak
tight and resistant to higher temperature exhaust and condensate
that forms in the exhaust gas stream.
[0040] As shown in FIG. 7, the furnace 21 is provided with a main
circulation fan 92 that draws a flow of air, generally indicated at
reference number 94, from rooms of a house and pushes the flow of
air 94 through a heat exchanger 96 around an exterior surface of
combustion tubes 98 or combustion chamber, depending on style of
furnace, wherein the flow of air 94 is heated and returned back
into the rooms of the house.
[0041] Separated from the main circulation fan 92 and the duct work
that contains the air flow 94 is a vestibule 100 of the furnace 21
and the blower 18 of the present invention. Preferably, the blower
18 is positioned on the blower mounting surface 20 in the vestibule
100 of the furnace 21. The motor casing 26 extends outward into the
vestibule 100 with the second side wall 48 of the blower housing 24
mounted adjacent the discharge port of the combustion
tubes/combustion chamber 98. The second section 90 of the impeller
70 in the blower 18 draws combustion air, generally indicated at
102, into the vestibule 100 from a furnace room in the house
through louvers 104 in a side and top structure of the furnace 21.
Then, the second section 90 of the impeller 70 draws the combustion
air 102 into the combustion tubes/combustion chamber 98 and into
the intake 66 of the blower housing 24 before expelling combustion
products, generally indicated at 106, out the discharge exit 56 and
into an exhaust pipe 108.
[0042] The first section 88 of the impeller 70 draws cooling air,
generally indicated at 110, from the vestibule 100 through the vent
holes 38 and the motor casing 26, out through the motor casing
opening 44, and into the blower housing 24 through the shaft hole
64. The cooling air 110 is then mixed with the hot combustion
products 106 as the impeller in the volute of the blower housing
compresses the gases 106,110. The cooling air 110 cools the motor
and the motor casing 26 as it is drawn through the motor casing 26
and lowers the temperature of the combustion products 106. Due to
the location of the exhaust pipe 108 of the furnace 21 in the
vestibule 100, the lower combustion products 106 temperature lowers
the temperature of the vestibule 100. In a typical furnace, the
vestibule chamber interior also contains the electronics and
controls 111 to control the operation of the blower and furnace 21.
The flow of air 102 being drawn into the vestibule 100 along with
the lower vestibule temperature cools the control electronics
111.
[0043] As shown in FIG. 8, the arrangement of the blower in a high
efficiency furnace 21' produces flow paths through the furnace 21'
that are similar to those described above with reference to the low
efficiency furnace 21 of FIG. 7. The blower 18 draws the combustion
air 102 into the vestibule 100 before entry in the combustion
tubes/combustion chamber 98. The blower 18 is positioned in the
vestibule 100 where the first section 88 of the impeller 70 may
draw cooling air 110 directly from the vestibule 100 and through
the motor casing 26. The second section 90 draws combustion
products 106 into the blower where the combustion products are
mixed with the cooling air 110 and discharged out the exhaust pipe
108. Because in the high efficiency furnace 21' the combustion air
102 is drawn from outside the house, the vestibule 100 is provided
with an inlet pipe 112.
[0044] FIG. 9 shows an alternate embodiment of a low efficiency
furnace 21" in which the blower 18 of the present invention is
installed. In this embodiment, combustion air 102 is drawn into the
vestibule 100 through louvers 104 in a top structure of the furnace
21". The flow of combustion products 106 and cooling air 110
through the blower 18 is similar to that described above with
reference to FIG. 7.
[0045] The blower of present invention provides improved cooling
for the blower motor and the several other advantages described
above. The blower may be used in a furnace or other type of
appliance such as a hot water heater or clothes dryer or any other
Category I or III fuel burning appliance where combustion products
must be actively evacuated from the appliance through a chimney.
The blower motor may be a single speed motor, or a variable or
multi-speed motor, depending on design choice.
[0046] The control 111 for a furnace may be an integrated control
in the form of a computer or other digital circuit, as is commonly
found in present day designs, and its operating parameters may be
determined by software loaded into the control. Alternatively, or
in conjunction therewith, the installer or even a serviceman may be
provided access to check and even alter these settings through a
keyboard or other input device which may be connected to the
control or with a control panel provided. Various kinds of controls
may be used and even electromechanical controls provided with a
discrete timer which may be set to achieve the purposes of the
present invention.
[0047] The present invention includes a control that may be set,
either in software or hardware or otherwise, to provide a run time
after a combustion cycle during which ambient air is introduced
into the vent or exhaust flue. Attached hereto are Exhibits A and B
of data generated by the VENT II program which demonstrate the
effectiveness of the present invention. Exhibit A represents
essentially a "worst case" scenario for a typical installation in
which the furnace has been chosen to be a 100,000 btu, 80.5 percent
efficiency furnace with a 1 foot vertical and 5 foot horizontal 6
inch flue feeding a 20 foot chimney with an 8 minute combustion
time every 20 minutes. With these conditions, as simulated in the
program, it has been found that a dry chimney can be achieved with
as short as a 3 minute run time after each combustion cycle.
Exhibit B is the data for the same installation, except that the
furnace is 83 percent efficient, in which a dry chimney can be
achieved with as short as a 4 minute run time after each combustion
cycle. Thus, using the computer program developed and used to
generate data for the Gas Research Institute Topical Report
referenced above, a simulation has been shown to achieve a dry
chimney for an 83 percent efficient appliance which was impossible
to achieve with the operating modalities reported therein.
[0048] While the present invention has been described by reference
to specific embodiments, it should be understood that those
embodiments are intended by the inventors to be merely illustrative
and not limiting. Modifications and variations of the invention may
be constructed without departing from the scope of the invention as
defined by the following claims and their legal equivalents. For
example, while the inventors have demonstrated the operability of
the invention in the context of a typical installation, it is noted
that an idealized run time may be calculated for each installation.
However, it is anticipated that appliance manufacturers will set
the "run time" at the factory to be more than adequate for every
expected installation both for safety and ease in manufacture.
Other factors which the furnace manufacturers may take into account
are the desire to shorten the "run time" to minimize the noise that
the furnace makes within the home as well as the energy usage of
the combustion fan. Furthermore, the blower motor may well be a
variable speed or multi-speed motor so that it may be run at a
different speed during the run time than during combustion. For a
shortened run time, the motor may perhaps be run at a faster speed.
For a less objectionable noise level, the motor may perhaps be run
at a slower speed. These kind of parameters could be determined as
a matter of design choice by a routineer in the art and to satisfy
the preferences of the designer and are thus not seen to be
critical to the invention. This "safe" run time may be well in
excess of any calculated "worst case" scenario of a typical
installation that resulted in the 3 minute run time disclosed in
the preferred embodiment. For example, a 6 minute run time may be
chosen. However, care will need to be taken to avoid the apparently
limiting case demonstrated in the Gas Research study that found
that a continuous run time was not effective, even for an 80.5
percent efficient furnace, in achieving a dry chimney in a typical
installation. Furthermore, the post-purge run time of the prior art
has not been demonstrated to achieve a dry chimney, being
apparently under a minute at its longest, and hence provides a
lower limit than the 3 minute limit known to the inventors.
[0049] While the inventors have determined that a pre-selected,
fixed, and repetitive run time is effective in achieving the
purposes of the invention, it may be that further experimentation
would demonstrate that the run time could be varied and yet the
chimney would be dry. For example, the run time could be calculated
at the end of each combustion cycle as a fraction or otherwise be
related to the actual combustion cycle time, so that the run time
would vary for each combustion cycle. For an 8 minute combustion
cycle, a 75% run time would require a 6 minute run time. Should the
furnace require a 4 minute combustion cycle to heat the house,
given the outside temperature and other factors present at that
moment, then a 3 minute run time would occur. Thus, with this
operating modality, a different run time would be used after each
combustion cycle and yet the data might very well demonstrate a dry
chimney had been achieved. Additionally, it could be that a run
time could be provided after fewer than every combustion cycle and
yet still achieve a dry chimney within the parameters of the
appropriate standard. For example, a run time could be provided
after every other combustion cycle, or every two out of three
combustion cycles, etc.
[0050] As the control is typically an electronic logic device,
including a microprocessor, an even more sophisticated operation
may be provided wherein the computing and monitoring capabilities
of the control could be more fully utilized. For example, the
control will have data corresponding to the frequency at which the
appliance is operating as well as the time period for each
combustion cycle. The control could thus use this information to
custom calculate and effect a run time and frequency adapted to a
particular, and ever changing, operating environment. As anyone can
appreciate, an appliance such as a gas fired furnace will
experience a differing operation or duty cycle comprising a
differing frequency and duration of combustion depending on many
variables including the particular home within which it is
installed, the particular temperature of the day, sun loading, the
setting of the home thermostat, the relative humidity both inside
and outside the home, the efficiency of combustion including the
air/gas mix, etc. All of these variables have an impact on the
furnace duty cycle, but the furnace typically runs in response to
the single setting of a thermostat. Similarly, the furnace
manufacturer may not want to set the control for a fixed run time
after combustion and instead allow the control to be more
responsive to the actual conditions experienced by the furnace, as
evidenced by its duty cycle. The inventors believe that a person of
ordinary skill in the art, using the teaching of the present
invention, could readily determine what range of run times and
corresponding frequencies for after combustion blower operation
would be required for a given furnace duty cycle in order to
achieve a dry chimney. Furthermore, it is anticipated that there is
some readily determinable working relationship between the blower
run time duration and frequency such that a control could be set to
optimize either for a minimum run time or a minimum frequency, or
to optimize both in combination to suit the designer's preferences.
In this way, the control could take a more active role in
determining the post combustion blower run time and frequency to be
used for any given operational cycle as experienced by the
appliance.
[0051] These different kind of operating modalities are considered
by the inventors to be within the scope of the present
invention.
[0052] Still another advantage of the present invention is its
versatility. It can not only be used with the fanless motor cooling
invention of the parent, but may also be used with a prior art
induced draft furnace or other appliance. It is only required that
the appliance have a combustion fan which may be operated after a
combustion cycle to provide dilution or ambient air into the
chimney.
[0053] As mentioned above, the embodiments disclosed herein are
intended to be illustrative and the invention is intended to be
limited solely by the scope of the claims appended hereto and their
legal equivalents.
* * * * *