Abstract:
An unvented gas fireplace in which air flow through a dosed combustion chamber is controlled by means of a restriction in the air flow path through an outer plenum chamber surrounding the combustion chamber, causing a pressure differential between the plenum and combustion chamber, forcing air from the plenum into the combustion chamber, where it is combusted and mixed with the cool air that has passed the restriction in the plenum, before the air mixture is exhausted into the surrounding room or area. A diverter selects between exhausting the heated air in the same or the opposite side as the air intake. The unit may be used as an outdoor stand-alone fireplace.

Description:
FIELD OF THE INVENTION 
       [0001]    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 
       [0002]    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. 
         [0003]    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. 
         [0004]    U.S. Pat. No. 2,696,205 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 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. 
         [0005]    U.S. Pat. No. 5,054,468 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. Pat. No. 5,139,011 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. 
         [0006]    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. 
         [0007]    U.S. Pat. No. 5,678,534 to Fleming and U.S. Pat. No. 5,906,197 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 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. 
         [0008]    U.S. Pat. No. 6,425,390 to Campbell and U.S. Pat. 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 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. 
         [0009]    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 
       [0010]    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. 
         [0011]    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 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. 
         [0012]    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. 
         [0013]    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. 
         [0014]    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 plenum through a combustion air outlet between the restriction and the ambient air outlet. 
         [0015]    The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which: 
           [0017]      FIG. 1  is a side sectional schematic view of an unvented gas fireplace according to an embodiment of the invention; 
           [0018]      FIG. 2  is a side sectional schematic view of an unvented gas fireplace according to another embodiment of the invention; 
           [0019]      FIG. 3  is a front view of the unvented gas fireplace of  FIG. 2  with the combustion chamber removed; 
           [0020]      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; 
           [0021]      FIG. 5  is a side sectional schematic view of the third embodiment with the diverter in a second position; 
           [0022]      FIG. 6  is a front perspective view of a standalone outdoor embodiment of the invention with the diverter in a first position; 
           [0023]      FIG. 7  is a front perspective view of a stand-alone outdoor embodiment of the invention with the diverter in a second position; and, 
           [0024]      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 
       [0025]    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 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 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. 
         [0026]    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 . 
         [0027]    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 . 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 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. 
         [0028]    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 . 
         [0029]    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. 
         [0030]    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 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 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. 
         [0031]    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). 
         [0032]    In the first position shown in  FIG. 4 , the combined combustion and excess drawn air flow is directed to the exterior of the budding 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. 
         [0033]    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 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 . 
         [0034]    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.