Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF INVENTION
UNVENTED GAS FIREPLACE
FIELD OF THE INVENTION
This invention relates to an improved unvented gas fireplace. In particular,
the
invention relates to an unvented linear gas fireplace in which the air flow
into a
unvented closed combustion chamber is controlled by a restriction in the path
of the
air flow through a plenum chamber around the combustion chamber.
BACKGROUND OF THE INVENTION
Gas-fired fireplaces are becoming extremely popular because they are generally
cleaner, safer and less expensive to build than wood-fired fireplaces.
Unvented gas-
fired fireplaces in particular have become increasingly popular, because they
allow
the consumer to fit or retrofit a fireplace into any pre-existing room having
a gas line,
without incurring the costs associated with chimney construction or
construction of a
venting system. Further, because unvented fireplaces do not require chimneys
or
flues, it is possible to locate the fireplace in practically any location. For
example,
the fireplace may be located against a wall, or in a corner, or in the middle
of a room,
where the flame is visible from two or more sides. The fireplace may also be
of any
shape and size, depending on the location in which it is to be installed.
Such fireplaces are considered to be highly efficient, drawing room air in for
combustion and returning the warmed air directly to the room. However, because
unvented fireplaces vent most or all of the combustion products to the
directly to the
room rather than outside, they must meet rigid standards, requiring that the
fireplace
burn extremely efficiently in order to minimize the buildup of the combustion
products.
U.S. Patent No. 2696205 to Ruhl describes a space heater that operates
similarly to
a typical unvented fireplace. The heater comprises a heater unit surrounded by
a
series of flues and baffles. Ambient air passes through the heater section,
where it
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is combusted by a flame within a metal radiant element. The flow of the
combustion
air from the heater to the surrounding room is partially controlled by a
deflecting
choke surface, which accelerates expulsion of the heated air by increasing the
air
pressure at the choke. A second stream of air also freely flows behind the
heater
unit, through the flues and out the baffles. This second stream of air is
warmed by
thermal contact with the flues and thus also warms the room, but in addition
it serves
a cooling function, ensuring that the area immediately around the rear of the
heater
does not get too hot.
.io U.S. Patent No. 5054468 to Moon et al. describes an unvented fireplace
assembly
consisting of two chambers, namely a combustion chamber surrounded by a plenum
chamber. Ambient air moves through the plenum chamber, warming by contact with
the outside of the combustion chamber, before returning to the room in which
the
fireplace is located. Air is also pulled directly into the combustion chamber
by a fan;
the heated combustion air is then expelled back into the room. U.S. Patent No.
5139011 to Moon describes a similar unvented fireplace with a pair of airflow
paths.
Ambient air passes through a duct assembly around the combustion chamber,
heating the air before returning it to the room. Combustion air is again
pulled directly
into the combustion chamber by a fan and heated before being returned to the
room.
Each of these patents uses a dual intake system, which makes the system more
complex, and makes it difficult to maintain a steady flow of air into both
airflow
pathways. If air moves relatively quickly into the combustion chamber, for
example,
there may not be sufficient plenum airflow to cool the area outside the
combustion
chamber. Further, in each of these cases, the combustion air and the plenum
air are
expelled into the room at different places and likely at different rates. The
combustion air is hotter than the radiantly heated plenum air, which can lead
to
undesirable localized temperature variations.
U.S. Patent No. 5678534 to Fleming and U.S. Patent No. 5906197 to French each
disclose a single-intake fireplace in which the incoming airflow is divided
into several
pathways, one flowing to the combustion chamber, and the others flowing to
various
convection pathways or plenum chambers surrounding the combustion chamber.
The air from the plenum or convection areas is then mixed with the combustion
air
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before being returned to the room. In order to minimize the combustion
products
being expelled into the room, the combustion air passes through a catalytic
converter
to convert any combustion products to carbon dioxide and water before the
combustion air mixes with the plenum air and re-enters the room.
U.S. Patent No. 6425390 to Campbell and U.S. Patent No. 5,701,882 to Champion
each disclose a gas fireplace in which combustion air is drawn directly into
the
combustion chamber while a second pathway for room air is provided in one or
more
plenum chambers surrounding the combustion chamber. Neither Campbell nor
io Champion disclose a combustion chamber that is essentially sealed from the
surrounding room, meaning that there is little to no control over the amount
of air
passing into the combustion chamber. This may adversely affect the appearance
of
the flame and the efficiency of burning within the combustion chamber.
It is therefore an object of this invention to provide an unvented gas
fireplace that
overcomes one or more of the disadvantages found in the prior art fireplaces
referred to above.
SUMMARY OF 'THE INVENTION
The invention comprises an unvented gas fireplace in which air flow through a
closed
combustion chamber is controlled by means of a restriction in the air flow
path
through an outer plenum chamber surrounding the combustion chamber. The
restriction in the air flow path through the plenum chamber causes a pressure
differential between the plenum and combustion chambers. The relative increase
in
plenum chamber pressure forces air into the combustion chamber, where it is
combusted and mixed with the air in the plenum chamber before the air mixture
is
exhausted into the surrounding room.
In one aspect, the invention comprises an unvented gas fireplace comprising a
closed combustion chamber; a plenum outside of the combustion chamber, the
plenum having an ambient air intake to receive air from a room in which the
fireplace
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is located, and an ambient air outlet to exhaust air into the room; the plenum
comprising a restriction, the restriction adapted to cause a positive air
pressure
differential between the plenum and the combustion chamber, upstream of the
restriction; wherein the increase in air pressure forces air into the
combustion
chamber through a combustion air intake between the combustion chamber and the
plenum; and wherein heated air is exhausted from the combustion chamber into
the
plenum through a combustion air outlet between the restriction and the ambient
air
outlet. The fireplace may further comprise at least one blower to pull air
into the
ambient inlet, and may comprise ducting between the ambient inlet and the
blower.
In a further aspect of the invention, the heated air from the combustion
chamber may
be mixed with cool air in the plenum before exhausting the mixed air from the
fireplace.
In another aspect, the invention comprises a method of heating a room with an
unvented gas fireplace having a plenum outside of a closed combustion chamber,
comprising the steps of receiving a flow of ambient air from the room into the
plenum; restricting the flow of ambient air at a restriction in the plenum to
create a
positive air pressure differential between the plenum and the combustion
chamber
upstream of the restriction, and thereby force air from the plenum into the
combustion chamber through a combustion air intake; exhausting heated air from
the
combustion chamber to the plenum downstream of the restriction; mixing the
heated
air with cool air within the plenum to form warm air; and exhausting the warm
air to
the room. In a further aspect, the method may comprise the additional step of
blowing ambient air from the room into the plenum through an ambient air
intake.
In yet another aspect, the invention comprises an unvented gas fireplace
comprising
a closed combustion chamber; a plenum outside of the combustion chamber for
carrying air from an ambient air intake to an ambient air outlet; the plenum
comprising a restriction, the restriction adapted to cause a positive air
pressure
differential between the plenum and the combustion chamber, upstream of the
restriction; wherein the increase in air pressure forces air into the
combustion
chamber through a combustion air intake between the combustion chamber and the
plenum; and wherein heated air is exhausted from the combustion chamber into
the
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plenum through a combustion air outlet between the restriction and the ambient
air outlet.
The foregoing may cover only some of the aspects of the invention. Other
aspects of the invention may be appreciated by reference to the following
description of at least one preferred mode for carrying out the invention in
terms
of one or more examples. The following mode(s) for carrying out the invention
is
not a definition of the invention itself, but is only an example that embodies
the
inventive features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described by reference to the detailed description of
the
preferred embodiment and to the drawings thereof in which:
Fig. 1 is a side sectional schematic view of an unvented gas fireplace
according to an embodiment of the invention;
Fig. 2 is a side sectional schematic view of an unvented gas fireplace
according to another embodiment of the invention;
Fig 3 is a front view of the unvented gas fireplace of Fig. 2 with the
combustion chamber removed;
Fig. 4 is a side sectional schematic view of a third embodiment of the
invention straddling a wall of a building with a selectable diverter in a
first
position;
Fig. 5 is a side sectional schematic view of the third embodiment with the
diverter in a second position;
Fig. 6 is a front perspective view of a stand-alone outdoor embodiment of
the invention with the diverter in a first position;
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Fig. 7 is a front perspective view of a stand-alone outdoor embodiment of the
invention with the diverter in a second position; and,
Fig. 8 is a rear perspective view of a stand-alone outdoor embodiment of the
invention with the diverter in the second position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A first embodiment of the fireplace of the invention is shown in Fig. 1.
Fireplace 10
comprises a combustion chamber 12 at least partially within an outer or plenum
to chamber 14. Combustion chamber 12 is closed with respect to the room in
which
the fireplace 10 is located, in that combustion air intake 16 and combustion
air outlet
18 of combustion chamber 12 are not in direct communication with the
surrounding
room. Rather, combustion air intake 16 receives air only from plenum 14 and
combustion air outlet 18 exhausts only into plenum 14. Panels 20 are provided
on
is one or more sides of combustion chamber 12; these panels may be glass or
any
other suitable transparent material to permit viewing of the flame 30 within
the
combustion chamber 12, or may be metal or any other suitable opaque material
if
such viewing is not required.
20 Air from the surrounding room accesses fireplace 10 through ambient air
intake 22 in
the plenum 14, while air is exhausted from fireplace 10 through ambient air
outlet 24
of plenum 14. Blower 26 may be used at or near ambient air intake 22 to draw
air
into plenum 14.
25 Under startup conditions, air entering the fireplace 10 through ambient
air intake 22
will preferentially remain in plenum 14, flowing along path 28, without a
great deal of
air entering combustion air intake 16, because the size of path 28 is much
greater
than that of combustion air intake 16. However, path 28 is provided with
restriction
32, a relatively narrow section of path 28, which restricts the air flow
through path 28.
30 This backs up the air between restriction 32 and blower 26, causing a
positive
pressure differential between plenum 14 and combustion chamber 12, upstream of
the restriction. The pressure differential forces air in plenum 14 to enter
combustion
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chamber 12 through combustion air intake 16, which is preferably located below
the
flame 30, and which may take the form of one or more openings arranged in any
suitable pattern. The air is heated within combustion chamber 12, and rises
above
the flame, where it escapes through combustion air outlet 18, which may also
take
the form of one or more openings arranged in any suitable pattern. The
pressure
differential between plenum 14 and combustion chamber 12 therefore helps to
maintain the pressure and air velocity within combustion chamber 12, by
forcing air
through the chamber 12 without over-pressurizing it.
io Restriction 32 is shown in Fig. 1 as being in an upper part of path 28,
but it will be
understood that it may be located anywhere within plenum 14 along path 28
between
combustion air intake 16 and combustion air outlet 18.
Air entering combustion chamber 12 assists in the combustion reaction to
create
flame 30 and hot air, which exits the combustion chamber 12 at combustion air
outlet
18. When the hot air exits combustion chamber 12 into path 28 in plenum 14, it
may
exhaust directly into the room or to the outside, or it may mix with
relatively cool air
that has flowed along path 28 through restriction 32. The combination of hot
and
cool air flows creates a warm air flow that exhausts to the surrounding room
or to the
outside at ambient air outlet 24. Combustion air outlet 18 is shown as being
at the
top of combustion chamber 12, which may be preferred because the heated air
will
naturally rise towards the combustion air outlet 18. However, it will be
understood
that combustion air outlet 18 may appear anywhere in path 28 between
restriction 32
and ambient air outlet 24. Factors such as the preferred time available for
the
heated air to mix with the cool air flowing through path 28 may influence the
exact
location of combustion air outlet 18. It will also be understood that path 28
can be of
any preferred shape and length, such that ambient air outlet 24 terminates at
any
desired point, such as at the top of the fireplace 10 (as shown in Fig. 1) or
anywhere
along the bottom or side of the fireplace 10, thus providing a stream of warm
air to
the surrounding room or to the outside at any desired point.
Another embodiment of the unvented fireplace 10 of the invention is shown in
Figs. 2
and 3. This embodiment works essentially in the same manner as the embodiment
described above, although in this embodiment, blower 26 of Fig. 1 is replaced
by one
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or more backward inclined blowers 34. Further, blower 34 (or an equivalent fan
or
blower assembly) may be placed anywhere suitable within path 28, and
additional
ducting 36 may be used as necessary between ambient air intake 22 and blower
34.
Blower 34 draws air into plenum 14 through ducting 36, and distributes it
throughout
the plenum 14. Restriction 32 causes an increase in air pressure in the plenum
14,
forcing air from plenum 14 through combustion air intake 16 (which may take
the
form of one or more openings arranged in any suitable pattern), and into
combustion
chamber 12. The combustion air rises towards the top of combustion chamber 12
as
it is heated. The air then passes out of combustion chamber 12, where it may
be
io exhausted directly to the ambient room in which the fireplace is located or
to the
outside, but preferably it is exhausted into path 28 of plenum 14 via
combustion air
outlet 18. The heated combustion air mixes with cool air that has flowed along
path
28 past restriction 32, creating a warm air mixture that may be vented through
ambient air outlet 24. Again, it will be understood that path 28 can be of any
preferred shape, such that ambient air outlet 24 terminates at any desired
point
along the top, bottom or side of the fireplace 10, thus providing a stream of
warm air
to the surrounding room or to the outside wherever it is preferred.
A third embodiment is shown in Figs. 4 and 5. The fireplace according to this
embodiment is provided in an external wall 40 of a building such that one side
42 of
the unit faces the outside 44 of the building and the opposite side 46 of the
unit faces
the interior 48 of a room of the building. Air is drawn into the unit by
intake opening
50 on the outdoor side of the unit. Incoming air is drawn by blower 52 into
passageway 54. A portion of the air in passageway 54 passes into the
combustion
chamber at 56 and a portion is driven past restriction 58.to mix with air and
combustion gases exiting the combustion chamber at chamber outlet 60. The
combined air flow is directed down a passageway 62 that is preferably formed
of two
spaced transparent panels 64, 66 allowing viewing into the firebox from the
outside
of the building as well as from the inside of the building through two spaced
transparent panels 68, 70. A diverter 72 is operable by a user to pivot
between a
first position shown in Fig. 4 and a second position shown in Fig. 5. by means
of a
knob (not shown).
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In the first position shown in Fig 4, the combined combustion and excess drawn
air
flow is directed to the exterior of the building by outlet 74. In the second
position
shown in Fig. 5, the combined air flow is directed to outlet 76 that exhausts
to the
inside of the building.
In yet a further embodiment, shown in Fig. 6, the fireplace is provided as a
standalone outdoor unit 80 rather than straddling the exterior wall of a
building.
According to the preference of the user, the relatively warm exhaust air may
be
directed to one side or the other of the unit, for example to accommodate
where
io people may be seated around the fireplace. In Fig. 6, the diverter 72 is
in the first
position corresponding to Fig. 4 in which the air intakes 82, 84 are on the
same side
as the air outlet 86. Fig. 7 illustrates the standalone outdoor unit wherein
the diverter
is in the second position corresponding to Fig. 5 in which the air is outlet
at 88 to the
opposite side of the unit. This allows the user to select the direction of
exhaust of
relatively warm air depending on the location of the standalone unit, the
location of
persons seated around the unit and the ambient outdoor temperature. Fig. 8
shows
the outlets at the rear of the standalone unit with the diverter in the second
position.
As in the embodiment of Figs. 4 and 5, the panels forming the air passageways
along the sides of the unit are transparent to allow viewing of the firebox
from either
the front or the back of the unit 80.
It will be appreciated by those skilled in the art that the preferred
embodiment has
been described in some detail but that certain modifications may be practiced
without departing from the principles of the invention.
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