Abstract:
A concentric air diffuser for use with climate control systems to direct air to desired locations within the interior of a building and return air to the system includes a perforated plate between a supply inlet and supply vents. The perforated plate assists in balancing air flow out of the vents. Additionally, a baffle plate is located along the portion of the perforated plate below the supply inlet to assist in distributing air throughout the diffuser housing prior to allowing the air to flow through the clear area portion of the perforated plate and out through the vents.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to the area of heating, ventilating and air-conditioning systems including the elevated components through which air is supplied to a space to be ventilated and also returned to the system. More specifically, this invention relates to ceiling-mounted concentric air diffuser plenums for use with a climate control system. 
     2. Description of Related Art 
     Climate control systems such as heating, ventilation and air-conditioning systems (HVAC systems) are often utilized in buildings to provide a comfortable climate within the building. Some buildings utilize ducts within the building to direct air from a climate control unit to specific locations for further distribution throughout a desired space. Other buildings may utilize multiple climate control units in a system in an effort to minimize the length and quantity of ducts within the building. In some buildings, especially buildings of a commercial nature, the climate control system, often comprising a number of climate control units, is mounted on the roof. Preferably the roof is a flat roof immediately above a living or working space, although the air diffuser plenum of the preferred embodiments could be utilized in conjunction with pitched roofs and/or ductwork. 
     Concentric diffusers are useful to provide a single diffuser housing to supply ventilation to a space while also allowing for return air to be returned to the HVAC system. Typically supply air is provided through at least one inlet into the diffuser from the HVAC outlet to the diffuser vents, or outlets, while return air is returned through at least one return outlet of the diffuser to the HVAC system. Concentric air diffusers are often mounted in drop ceilings to minimize the number of locations for vents in ceilings since one diffuser may be used for both supply and return air. 
     One problem with typical concentric diffusers is the imprecise flow of air from different portions of the diffuser. Specifically, in a drop box type diffuser where air is supplied to a space through four lateral sides of the diffuser, manufacturers often advertise a particular cubic feet per minute of air distribution from the diffuser. For instance, for a 5-ton HVAC unit with 18 inch supply ducting and side vents twice the length of the end vents, the manufacturer may advertise a total of 2,000 cubic feet per minute supplied from the diffuser: 500 cfm from each end and 1,000 cfm from each side. In actuality, the diffuser may supply 875 cfm from a side and 825 cfm from an end at velocities at specific locations including 1750 feet per minute at a location along the end closest to the supply inlet of the diffuser while as little as 600 feet per minute at a portion of the opposite end. Thus, the supplied air is imbalanced. 
     Some manufacturers advertise that baffles may need to be installed after installation of the diffuser in order to balance air flow at that time. The problem with this method of balancing air flow is that with the diffuser installed with a ceiling, access may only be obtained at and through the vents since the top shroud often extends into the ceiling. In order to balance air flow some technicians may shut portions of the slats in the vents while opening other vent slats to a further degree. Unfortunately, when a vent slat is moved closer to the closed position, it may tend to vibrate and make more noise due to the relatively large amount of air attempting to rush through narrower openings in the vent. If the vents do not have moveable slats, then other methods may be necessary. 
     Accordingly, a need exists to provide balanced air flow out of a concentric diffuser without requiring measurements or adjustment of air flow after installation. 
     Another need exists to provide an internal baffle system which does not add additional noise to a diffuser. 
     Another need exists to provide a relatively inexpensive means for providing balanced air flow without requiring special measuring equipment or skills on the part of an operator. 
     It is therefore desirable to provide an improved concentric air diffuser. 
     Furthermore, a need exists for a more efficient air diffuser capable of more precisely directing air than has been known in the prior art. 
     It is therefore desirable, to have an improved air diffuser plenum. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a concentric air diffuser plenum for use with climate control systems to direct air to desired locations within the interior of a building from a supply while directing return air to the climate control system through a return. An inlet in the diffuser receives air from the climate control system. An outlet in the diffuser directs air back to the climate control system. A perforated plate is located within the diffuser separating the vents from the supply inlet. A baffle plate may also assist in diverting air across the perforated plate. 
     The perforated plate allows pressure to accumulate within the shroud to provide a more balanced air flow through the vents since much of the turbulence which is normally present within the concentric diffuser is drastically reduced through the use of the perforated plate and the air is more evenly distributed throughout the diffuser. An internal baffle located near the diffuser inlet assists in distributing the air within the diffuser shroud prior to delivery supply air through the vents. 
     Accordingly, it is an object of the present invention to provide a concentric air diffuser with an internal perforated plate which may be relatively inexpensive to manufacture and provides relatively, if not extremely accurately, balanced air flow. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a bottom perspective view of a concentric air diffuser plenum of the drop box style. 
     FIG. 2 is a top perspective view of a prior art concentric diffuser similar to the diffuser of FIG.  1 . 
     FIG. 3 is a cross-sectional view of the prior art diffuser of FIG. 2 taken along line A—A with the shroud removed. 
     FIG. 4 is a top plan view of the prior art diffuser of FIG. 2 with the shroud removed. 
     FIG. 5 is a diffuser similar to the diffuser of FIG. 4 with an installed perforated plate along the line B—B of FIG. 3, with the shroud removed according to the present invention. 
     FIG. 6 is a top plan view of the diffuser of FIG. 5 including a baffle located substantially below the inlet supply for the diffuser in accordance with the preferred embodiment. 
     FIG. 7 is a bottom perspective view of a concentric air diffuser of the flush mounted style. 
     FIG. 8 is a top perspective view of a prior art concentric air diffuser similar to the diffuser of FIG.  7 . 
     FIG. 9 is a top plan view of the prior art diffuser of FIG. 8 with the shroud removed. 
     FIG. 10 is a cross-sectional view of a diffuser similar to the diffuser of FIG. 8 taken along the line A—A, with a perforated plate installed according to the present invention. 
     FIG. 11 is a top plan view of the diffuser of FIG. 10 with the shroud removed according to the present invention. 
     FIG. 12 is a top plan view of the diffuser of FIG. 11 including a baffle located substantially below the inlet supply for the diffuser in accordance with an alternating preferred embodiment. 
     FIG. 13 is a top perspective view of a prior art concentric air diffuser of the flush mounted style with two supply inlets and two return outlets. 
     FIG. 14 is a bottom plan view of the prior art concentric air diffuser of FIG.  13 . 
     FIG. 15 is a top perspective view of a prior art concentric air diffuser of the drop box style. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-6 and  15  are directed to drop box style concentric air diffusers. FIGS. 7-14 are directed to flush mounted concentric air diffusers. The principles of operation of both styles are similar in many respects. 
     FIG. 1 is a typical concentric air diffuser  10  having a supply inlet  12  and a return outlet  14  which cooperates with the supply and return ducting from an HVAC system such as a roof mounted HVAC unit. The diffuser  10  has a housing  16  comprised of a shroud  18  atop a bottom portion  20 . The embodiment shown in FIG. 1 has a drop box style bottom portion  20  illustrated while the embodiment in FIG. 7 illustrates a flush mount diffuser  110  having a flush mounted lower housing  120 . In concentric air diffusers  10 ,  110  the supply air portion of the diffusers  10 ,  110  is separated from, or not in communication with, the return air portion. 
     Referring back to FIG. 1, the bottom portion  20  has vents  22  for supplying air to a space and a return air inlet  24  for returning air to the return outlet  14  for receiving air from a space. The shroud  18  has opposing ends  26  and opposing sides  28 . The bottom portion  20  has opposing ends  30  and opposing sides  32 . This style diffuser is often adapted to be installed in a drop ceiling. Most drop ceilings utilize 2 ft.×2 ft. or 2 ft.×4 ft. ceiling tiles. Accordingly, the illustrated diffuser  10  may be installed in a 2 ft.×4 ft. ceiling opening. Of course, other sizes and shapes are also contemplated by this design. FIGS. 13-15 are other common concentric air diffusers having multiple air supply inlets and return outlets. These diffusers may also be adapted as described herein. 
     In the drop box configuration FIG. 1, the bottom portion  20  has a bottom surface  34  housing the return air inlet  24 . Comers  36  join the drop box ends  30  and sides  32  and may assist air to be directed through the vents  22 . Flange  38  may assist in locating the diffuser  10  relative to the ceiling to which it is normally installed. 
     FIG. 2 is a top perspective view of the diffuser  10  of FIG.  1 . FIG. 2 also shows the top of the shroud  44  with supply connection  40  and return connection  42 . Normally, the supply and return connections  40 ,  42  are cylindrical for cooperating with standard cylindrical ducting, however, other configurations could also be utilized. 
     FIG. 3 is a cross-sectional view of FIG. 2 taken along the line A—A with the shroud  18  removed. The bottom portion  20  is connected to the return air inlet  24 . The return air inlet  24  is in communication with the return air outlet  14 . The return cover  46  may cover at least a portion of return air inlet  24 . Additionally, the return portion of the diffuser  10  may be separated from the supply portion by backwall  48  and angled wall  54 . FIG. 4 also shows side walls  50 ,  52  which assist in separating the return portion of the diffuser  10  from the supply portion. Air enters through a supply inlet  12  at air entry  56  illustrated in FIG.  3 . With the shroud  18  installed, air is directed along the angled wall  54  into the bottom portion  20 . Air may escape through vents  22  in the bottom portion  20  to provide supply air to a space. The flange  38  is a convenient location to join the bottom portion  20  to the shroud  18  however other joining locations may be utilized. 
     FIG. 4 shows the side walls  50 ,  52 . As can be seen in this figure, air enters through a supply air inlet  12  and is contained within the shroud  18  and bottom portion  20  until delivered to the vents  22  on the sides of the bottom portion  20 . The angled wall  54  and the lower housing bottom  34  may assist in deflecting air out of the vents  22 . 
     Unfortunately, air entering through the supply inlet  12  may be turbulent and may not leave the diffuser vents  22  balanced in terms of air flow. Furthermore, the design of the most concentric air diffusers  10  does not adequately assist to evenly distribute air out of the vents  22 . Table A of the Appendix includes sample data from a five-ton air conditioning unit hooked to a standard concentric diffuser design. The manufacturer of this design advertises that baffles may need to be installed in order to balance air flow out of the vents  22  after installation. This would likely involve the adjusting of air flow out through the vents  22  which are at first end  68  and the first and second sides  62 ,  64  near the first end  68 . This would assist in pushing air towards the second end  60  of the diffuser  10 . Unfortunately, as some of the vents  22  are shut, the vents  22  may tend to vibrate or otherwise make noise thereby contributing to the noise of the diffuser  10 . This would be undesirable. 
     FIG. 5 shows at least a portion of the improvement of the present invention. A perforated plate  66  is installed at line B—B of FIG.  3 . This perforated plate  66  preferably contacts the return end wall  48 , return side walls  50 ,  52  and return angled wall  54  along the plane B—B illustrated in FIG.  3 . the perforated plate also preferably contacts the first end, second end, first side and second side  58 - 64  of the housing  12 . The perforated plate may overlap the flange  38  to assist in constructing the diffuser  10  of the preferred embodiment. The perforated plate  66  illustrated restricts the flow of air through the perforated plate  66 . As air enters through supply inlet  12  into the shroud  18 , the perforated plate  66  assists in distributing the air about the shroud  18  above the plate  66 . Although the pressure drop across the plate  66  is greater along plane B—B than would be without the plate  66 , the greater pressure differential is believed to dampen turbulence and assist in providing a more balanced air flow out of the vents  22 . 
     Although the illustrated perforated plate  66  has 51% free area, the perforated plate could have 60%, 68% or other amount of free area. One way to realize 51% free area is with a plate  66  having {fraction (3/16)}″ holes  70  spaced at ¼″ centers. The 68% free area perforated plate  66  would have ¼″ holes spaced at ⅜″ centers. It has been found desirable to include at least as much free area through the plate  66  as exists across the inlet  12  (i.e., for a round 18″ inlet, about 254 in. 2  of free area through the perforated plate  66  would be desirable in many applications). Although the perforated plate as shown as having holes  70 , other configurations including diamond shapes, squares, and others as known in the art. Additionally, the perforations may change along the length from the first end to the second end of the perforated plate  66  (i.e., 51% free area near the first end, but varying to 68% free area near the second end, etc.) The percent free area may also vary along the length (i.e., get progressively larger or smaller in value). 
     FIG. 6 includes baffle plate  68  which is illustrated below a portion of the supply inlet  12 . The baffle plate  68  is located substantially along the plane B—B of FIG.  3 . In the preferred embodiment, the baffle plate  68  is attached to the perforated plate  66  such as by screws or the like. The baffle plate  68  assists in directing the air supplied through the supply inlet  12  to other portions of within the shroud  18  before allowing supply air to proceed through the perforated plate  66  to the vents  22 . The baffle plate  68  of the preferred embodiment is illustrated contacting the angled wall  54  substantially along the length of the angle wall  54 . Furthermore, the baffle plate  68  may contain openings, curve portions, or other features which assist in balancing the air flow from the diffuser  10 . 
     After installing the perforated plate  66  and baffle  68  in the diffuser  10  and attaching the test equipment used to prepare Table A, the air flows of Table B were achieved. It is believed that with precise selection of the shape and size of the baffle portion  68  and the percent free area along the length from the first end  58  to the second end  60  of the perforated plate  66 , that a particular diffuser  10  may be made to be more balanced in terms of air flow. The baffle portion  68  utilized for this test was about 14 inches×12 inches and was positioned substantially as illustrated in FIG. 6 against the angled wall  54 . Specifically, with the rudimentary experiment performed, the air flow from the first end changed from 65% too much air to about 5% too little air. Air out the first side  62  was altered from 87% to 110% of desired flow. Air out the second end  60  changed from 100% to 108% desired flow and air flow out the second side  64  changed from 107% to 105%. 
     Furthermore, the velocity of air out of specific locations along the lengths of the perforated plate and the width of the perforated plate was much more evenly distributed as illustrated in Table B. At the first end  58  velocities varied between 1475 feet per minute to 1750 feet per minute before the installation of the plate  66  and baffle  68 . After the installation of the plate  66  and baffle  68  velocities varied between 1120 and 1200 feet per minute at any given location along the vent  22  of the first end  58 . Along the first side  62 , velocities varied from 1475 feet per minute to 500 feet per minute at certain locations. After the baffle plate  68  and plate  66  were installed, the velocities varied between -700 feet per minute and 1400 feet per minute, however, much more balanced air flow was exhibited along the length. Air from the second end  60  went from a range of 600 feet per minute to 1400 per minute before installation of the baffle  68  and perforated plate  66  to 1150 to 1370 feet per minute of the range. Accordingly, it may be observed that the installation of the perforated plate  66  and baffle  68  assisted in the distribution of more equivalent velocities out along the vents  22  from the ends  58 ,  60  and the sides  62 ,  64 . 
     The second style of common concentric diffusers is the flush mounted variety illustrated in FIG. 7 through 14. FIG. 7 shows diffuser  110  with supply inlet  112  and return outlet  114 . The diffuser housing  116  is comprised of a shroud  118  and a lower portion  120 , vents  122  are located on a bottom surface  123  of the lower portion  120  around the return air inlet  124 . The shroud has first and second ends  126 ,  127  and first and second sides  128 ,  129 . The ends and sides correspond with the first and second ends  158 ,  160  and first and second sides  162 ,  164  in a similar fashion as explained above for the drop box style diffuser  10 . The flange  138  of this style diffuser  110  is located proximate to the bottom portion  123  of the lower portion  120  such that the vents  122 , flange  138  and return air inlet  124  are substantially the only portion of the diffuser  110  visible when the diffuser  110  is installed into a ceiling as described above. FIG. 8 shows the top of the shroud  144  with supply inlet  112  and return outlet  114 . The supply connection  140  and  142  are also shown in this figure. The return grate  146  may cover the return air inlet  124 . 
     FIG. 9 is a top plan view of the lower portion  120  of the housing  116  with the shroud  118  removed. With the supply inlet  112  located substantially above the angled wall  154 , it is obvious that most diffusers of this type may provide imbalanced air with a majority of the air flowing out the first end  158  as opposed to the second end  160 . Just like in a drop box style configuration, the diffuser  110  is separated into supply and return portions. The return portion is separated from the supply portion by a rear wall  148 , two side walls  150 ,  152  and a front angled wall  154  within the diffuser housing  116 . 
     FIG. 10 illustrates a cross-sectional view of the alternatively preferred embodiment of the diffuser  110 . This view is taken along the line A—A of a diffuser  110  similar to that of FIG.  8 . As in the presently preferred embodiment  10 , the alternatively preferred embodiment  110  includes perforated plate  166 . The perforated plate  166  is spaced apart from the vents  122  to provide a space within the housing  116  for the supply air entering from supply inlet  112  to distribute along the top portion of the housing  116  prior to distribution through the perforated plate  166  prior to exiting the housing  116  through the vents  122 . The spacing of the perforated plate  166  from the vents  122  may vary based on the HVAC system selected, the size of the supply inlet  112  and other factors. It is anticipated that the spacing will be at least 1 inch, 2 inches, 4 inches, or 6 inches or other spaced apart distance from the vents  122 . 
     FIG. 11 illustrates a view of the lower portion  120  of the housing  116  with the shroud  118  removed. The perforated plate  166  is illustrated above and spaced apart from the vents  122 . Finally, FIG. 12 shows the insulation of baffle plate  168  relative to the angled wall  154  and perforated plate  166 . The actual location and shape of the baffle  168  and the percent free area of the perforated plate  166  maybe different in the flush mounted style diffuser  110  than in the drop box style diffuser  10 . Additionally, the percent free area may change along the length of the diffuser  110  from the first inlet  158  to the second  160  in a different manner than for the drop box style diffuser  110 . 
     FIGS. 13-15 are directed to other prior art diffusers which may be equipped with the improvement described and illustrated herein. Supply air from multiple supply inlets, and possibly sources, may be balanced utilizing the baffle system as described above. 
     Numerous alternations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.