Abstract:
A fume hood includes a top, bottom sidewalls, front panel and a back panel that define an enclosed workspace. The fume hood also includes a movable sash for opening and closing an access opening. The fume hood also includes an air chamber having an inlet in the front panel. The air chamber includes a baffle system that evenly distributes the inlet air as the air travels through the air chamber. An unimpeded flow of air is discharged downward and away from the breathing zone of the technician and proximate to the sash to reduce the forward momentum of air trying to escape the fume hood. In an alternate embodiment, the fume hood also includes a pressure pipe for drawing a small quantity of air from the air chamber and directing a flow of air between the movable sash and the header panel. This flow of air from the pressure pipe increases the relative pressure difference between the movable sash and the header panel of the fame hood. This design reduces the amount of condition air that is exhausted from the room through the fume hood, thereby lowering the operating cost and increasing the efficiency of the fume hood.

Description:
CROSS NOTING TO RELATED APPLICATIONS  
       [0001]    This application is a Continuation-In-Part of application Ser. No. 09/922,037 filed Aug. 3, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a fume hood apparatus, and in particular to a fume hood apparatus with an air chamber that allows a lower sash face velocity while maintaining fume containment, thereby improving fume hood performance.  
           [0004]    2. Description of the Related Art  
           [0005]    Fume hoods are protective enclosures that provide ventilated and illuminated workspaces for laboratory or other applications. A fume hood in its most basic form is a box with an inlet and an outlet. The inlet generally has a movable sash (vertically, horizontally or a combination of both), which provides an opening that allows access to the workspace. The procedures performed inside the fume hood are exhausted at the back through the top of the fume hood to a heating, venting and air conditioning (HVAC) system.  
           [0006]    An ideal fume hood system would use the least amount of conditioned room air possible while optimizing the containment levels necessary in order to perform the procedure. The need to exhaust less air is extremely important because it reduces the amount of conditioned air that is exhausted from the room through the hood, thereby lowering the operating cost of the fume hood.  
           [0007]    The inventors of the present invention have recognized this problem and have developed a fume hood that provides containment levels dramatically better than the current industry standard recommendations. In addition, the inventors have developed a fume hood that can be adaptable to fume hoods with different types of airfoils, such as a raised airfoil, or an airfoil that is flush with the work surface, and the like.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention comprises a fume hood apparatus including an enclosure, a movable sash and an air chamber. The air chamber includes an inlet for drawing air into the air chamber. Initially, the airflow travels upward into the air chamber. A backpressure redirects the airflow to travel downward through one or more baffles that evenly distribute the airflow within the air chamber as the airflow travels through the air chamber. A discharge positioned proximate to the face of the fume hood directs an unimpeded flow of air through the face of the fume hood. When the air moves into the fume hood around the technician&#39;s body a reverse vortex is created between the technician&#39;s body and face of the fume hood in the breathing zone. By directing an unimpeded flow of clean air downward across the breathing zone of the technician, the clean air from the air chamber reduces the forward momentum of air trying to escape the fume hood, thereby preventing airborne contaminants from escaping through the face of the fume hood. Airborne contaminants are prevented from escaping from the workspace even when the movable sash is fully opened resulting in improved containment performance.  
           [0009]    In an alternative embodiment of the invention, the fume hood includes an air chamber located in front of the movable sash and above the technician. As in the earlier embodiment, the air chamber draws room air in and redirects the airflow in a controlled manner down in front between the technician and the movable sash. In addition, the alternative embodiment includes a pressure pipe that draws in a small quantity of air from the air chamber and distributes the airflow between the backside of the movable sash and the front of the header panel. When the airflow that is directed out the bottom of the air chamber clears the bottom of the movable sash, the airflow is then drawn into the workspace and exhausted. The small quantity of airflow from the pressure pipe introduced between the movable sash and the front header sweeps the area clean and the airflow is also drawn into the workspace and exhausted. The air chamber in combination with the pressure pipe maintains fume containment at lower face velocities as compared to conventional fume hood designs.  
           [0010]    Various aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of the fume hood apparatus of the present invention;  
         [0012]    [0012]FIG. 2 is a perspective view of the air chamber of the present invention;  
         [0013]    [0013]FIG. 3 is a cross-sectional view of the air chamber taken along line  3 - 3  of FIG. 2;  
         [0014]    [0014]FIG. 4 is a cross-sectional view of an airfoil taken along line  4 - 4  of FIG. 3;  
         [0015]    [0015]FIG. 5 is a perspective view of the fume hood apparatus with the air chamber and a pressure pipe according to an alternative embodiment of the present invention;  
         [0016]    [0016]FIG. 6 is a perspective view of the air chamber with the pressure pipe according to the alternative embodiment of the present invention; and  
         [0017]    [0017]FIG. 7 is a cross-sectional view of the air chamber with the pressure pipe taken along line  7 - 7  of FIG. 6. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Referring now to FIGS.  1 - 4 , a fume hood apparatus is shown generally at  10  according to the present invention. The fume hood apparatus  10  generally includes an enclosure comprising a cover or top  12 , a bottom  14  opposite the top  12 , sidewalls including a first end panel  16 , a second end panel  18  opposite the first end panel  16 , a front panel  20 , and a back panel  22  opposite the front panel  20 . The enclosure may be made of metal or any other material of high strength and rigidity.  
         [0019]    The enclosure defines a workspace  24  and an access opening  26  through which a technician may reach into the workspace  24 . A moveable sash  28  is slidably mounted to the enclosure in a frame member  29  to allow the selective closing of the opening  26  and precluding access to the workspace  24 . The sash  28  is preferably made of glass or any other similar material. The technician may raise the sash  28  to allow access through the opening  26 , as shown in FIG. 1, or lower the sash  28  to close the opening  26 .  
         [0020]    The fume hood apparatus  10  may include a baffle system (not shown) that cooperates with a fan (not shown) to evacuate any fumes generated in the workspace  24 . Typically, the baffle system lies at the back of the workspace  24  and directs the fumes to a discharge conduit (not shown). As the fan draws the air and fumes out of the workspace  24 , ambient air flows into the workspace  24 , primarily through the opening  26 . The fume hood apparatus may also include a base member (not shown) to define a work surface and for positioning the fume hood apparatus  10  at a desired elevation for the technician, and an airfoil  27 . It will be understood that the invention is not limited by the type of baffle system, base member or airfoil, and that the invention can be practiced with any type of baffle system, base member, and airfoil well known in the art. Examples of a baffle system, a base member and an airfoil are described in U.S. Pat. No. 5,556,331 to Bastian, the entire contents of which are herein incorporated by reference.  
         [0021]    One aspect of the invention is that the fume hood apparatus includes an air chamber, shown generally at  30 , preferably located in the front panel  20  of the enclosure. In general, the air chamber  30  includes an upper portion  38 , a middle portion  44  and a bottom portion  50 .  
         [0022]    As best seen in FIG. 2, the middle portion  44  of the air chamber  30  includes an inlet  32  for outside or drawing room air into the air chamber  30  in the direction of arrows  33 . Preferably, the air is drawn into the inlet  32  of the air chamber  30  by a centrifugal fan  34  driven by a rotating means, such as a motor  35 . As best shown in FIG. 3, the air is drawn into suction  36  of the centrifugal fan  34  and exits the centrifugal fan  34  in an upward direction, as indicated by the arrows  37 , into the upper portion  38  of the air chamber  30 . In one embodiment of the invention, the centrifugal fan  34  provides an airflow in the range of between about 40 to about 250 cubic feet/minute through the air chamber  30 .  
         [0023]    The upper portion  38  is defined by an upper wall  39 , sidewalls  40 , and a baffle  41 . The baffle  41  includes a plurality of perforations or openings  42  for allowing a portion of the intake air to travel upward and pass through the openings  42 , as designated by the arrows  37 . It should be noted that the outlet of the centrifugal fan  34  is not positioned into abutting engagement with the baffle  41 , but is positioned at a predetermined distance from the baffle  41 . As a result, a portion of the intake air does not pass through the openings  42 , but impinges upon the baffle  41  and travels downward, as indicated by the arrows  43 . As a result, a backpressure is created within the upper portion  38  to redirect the airflow downwardly through the openings  42  of the baffle  41  and into the middle portion  44  of the air chamber  30 .  
         [0024]    The middle portion  44  of the air chamber  30  is defined by the baffle  41 , the sidewalls  40  and a baffle  45 . Similar to the baffle  41 , the baffle  45  includes perforations or openings  46 . The airflow travels downward, as indicated by the arrows  43 , through the middle portion  44  of the air chamber  30 . The middle portion  44  of the air chamber  30  may also include a baffle  47  with perforations or openings  48  that is positioned proximate to the baffle  45  to distribute the airflow more evenly as the air flows downward, as indicated by the arrows  49 , into a bottom portion  50  of the air chamber  30 . As best seen in FIG. 3, the baffles  45  and  47  are separated by a distance, “d”, in the range between about 0.10 and about 0.25 inches. At this separation distance, it has been found that the redirecting and distribution of the airflow into the bottom portion  50  is optimized. However, it will be appreciated that the separation distance, “d”, between baffles  45  and  47  can be any desired distance to optimize the redirecting and distribution of airflow into the bottom portion  50  of the air chamber  30 . Preferably, the bottom portion  50  extends the entire length of the air chamber  30 , unlike the middle portion  44  that houses the intake  32 , centrifugal fan  34  and motor  35 . As best seen in FIG. 4, the openings  48  of the baffle  47  are vertically and horizontally offset from the openings  46  of the baffle  45 . This configuration ensures that the airflow is evenly distributed as the airflow travels within the bottom portion  50  of the air chamber  30 . It will be appreciated that the invention is not limited by the degree in which the openings  46  and  48  are offset from each other, and that the invention can be practiced with any desired degree of offset.  
         [0025]    Referring now to FIG. 3, the bottom portion  50  of the air chamber  30  is defined by the baffle  47 , the sidewalls  40  and an air straightener  55 . The bottom portion  50  also includes a baffle  51  with perforation or openings  52  to allow the airflow to travel through the bottom portion  50 , as indicated by the arrows  53 . After passing through the baffle  51 , the airflow passes through an air straightener  55  having one or more ducts  56  for directing the airflow outwardly in a substantially uniformly linear direction from the air chamber  30 , as indicated by the arrows  57 . Referring now to FIG. 1, the fume hood apparatus  10  may include a discharge  58  to assist in directing the airflow from the air chamber  30 .  
         [0026]    It will be appreciated that the baffles  41 ,  45 ,  47  and  51  form a baffle system within the air chamber  30 . One purpose of the baffle system is to redirect and evenly distribute the airflow as it travels downward through the air chamber  30 . Although the baffle system of the invention includes baffles  41 ,  45 ,  47  and  51 , it will be appreciated that the number of baffles within the air chamber  30  to redirect and evenly distribute the airflow does not limit the invention. Thus, the invention can be practiced with any desired number of baffles that would evenly distribute the airflow as it travels downward through the air chamber  30 .  
         [0027]    One aspect of the invention is the location at which the airflow exits the air chamber  30 . Unlike conventional fume hood designs, the fume hood apparatus  10  of the invention directs the airflow at a location above the technician and between the technician and the movable sash  28 . Specifically, the discharge  58  is located immediately adjacent and proximate to the movable sash  28  in such a manner that a technician does not impede the airflow from the discharge  58 , unlike conventional fume hood designs. At this location, it has been found that the face velocity of the fume hood apparatus  10  is reduced while maintaining requirements for adequate containment of the fumes. It has also been found that the centrifugal fan  34  is required to operate when the access opening  26  has a minimum amount of surface area for a particular amount of airflow.  
         [0028]    As best seen in FIG. 1, the centrifugal fan  34  may only need to be operated when the movable sash  28  is positioned, for example, at or above a minimum height, “h”, of about  18  inches above the bottom  14  of the fume hood apparatus  10 . The centrifugal fan  34  can be switched on and off by any well-known type of switching means, such as a limit switch (not shown). Operating the centrifugal fan  34  only when the movable sash  28  is positioned at or above the minimum height, “h”, provides for a more energy efficient design as compared to a fume hood design in which the fan is continuously operated. Of course, the invention can be practiced with a continuously operated centrifugal fan  34 . In addition, the invention can be practiced with other types of fans. It should be noted that the air could be introduced into the air chamber  30  at other locations than the front panel  20 . For example, the air may be introduced into the top  12  or the sides  16  of the fume hood apparatus  10 .  
         [0029]    In addition, by providing an airflow at this location allows the fume hood apparatus  10  to maintain containment requirements even though the movable sash  28  is positioned above the minimum distance from the bottom  14  and the airfoil  27  is flush with the bottom  14 . This aspect of the invention provides a significant advantage over conventional fume hood designs in which the access opening must be reduced by requiring a raised airfoil and/or lower the movable sash  28  in order to achieve the required containment level at low face velocities.  
         [0030]    Referring now to FIGS. 5 through 7, a fume hood apparatus is shown generally at  10 ′ according to an alternative embodiment of the present invention. For brevity, the similar components of the fume hood apparatus  10 ′ are given the same reference numerals as in the fume hood apparatus  10  and will not be discussed below.  
         [0031]    The fume hood apparatus  10 ′ is substantially similar to the fume hood apparatus  10 , except that the fume hood apparatus  10 ′ includes a pressure pipe, shown generally at  60 . As best seen in FIG. 7, the pressure pipe  60  includes an inlet  62  preferably located in the upper portion  38  of the air chamber  30  in proximity to where the air exits the centrifugal fan  34  in the upward direction, as indicated by the arrows  37 . As best seen in FIG. 6, the air drawn into the inlet  62  of the pressure pipe  60  travels transversely, as indicated by the arrows  66 , along a straight portion  64  of the pressure pipe  60 , through a U-shaped portion  67 , through a downwardly extending portion  68 , and exits the pressure pipe  60  through an outlet  69 . The length of the straight portion  64  of the pressure pipe  60  is such that the movable sash  28  can move up and down to increase and decrease the access opening  26 , respectively. As best seen in FIG. 7, the outlet  69  is preferably located between the movable sash  28  and a header panel  70  of the fume hood apparatus  10 ′. As the air exits the outlet  69 , the air travels downwardly between the movable sash  28  and the header panel  70 , as indicated by the arrows  72 , and into the workspace  24 .  
         [0032]    One aspect of the alternate embodiment of the invention is that the pressure pipe  60  directs a small quantity of air from the air chamber  30  and distributes the air between the backside of the movable sash  28  and the front of the header panel  70 . Preferably, the quantity of air is between about 5 to about 15 cubic feet/minute, depending on the size of the workspace. This small airflow increases the relative pressure difference between the movable sash  28  and the header panel  70 , thereby minimizing contamination at low face velocities. In conventional fume hood designs, the negative static pressure inside the fume hood is reduced as the airflow through the fume hood is reduced. As a result, the relative pressure difference between the inside and the outside of the fume hood is so close that the contamination could migrate into the sash track or other small openings around the movable sash and escape into the surrounding room. The fume hood apparatus  10 ′ including the air chamber  30  in combination with the pressure pipe  60  of the invention provides containment levels dramatically better than conventional fume hood designs.  
         [0033]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.