Abstract:
An air circulation and conditioning system for a building in which the supply and return ducts are coincident and vent to a room so as to form air circulation in the room including an upward return air current surrounded by a downward supply current. An array of vents may be provided, each with a return duct opening and supply duct opening to create multiple air currents in the room. A wireway may be provided for co-locating electronics and communications network along the ductwork. A modular design air handling unit with multiple compatible modules providing different air treatment, purification, and monitoring functions may be provided. A method for retrofitting an existing single duct system into a dual duct system is provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to methods and systems for circulating and treating air in a building. 
       BACKGROUND OF THE INVENTION 
       [0002]    Typical heating, ventilating and air condition (HVAC) systems use supply ducts to supply air to a room and separate return ducts to draw air from the room. The ducts are typically connected to an air handling unit containing a motive source of circulation such as a blower. The supply and return ducts typically run along different routes. The supply and return ducts typically vent to the room at a relatively large distance away from one another. Typically, HVAC duct networks serve a singular purpose of conducting air flow. In addition, typical systems are thermodynamically inefficient and have inadequate air purification capability. 
         [0003]    There is a need for an HVAC system in which the supply and return duct runs are coincident and vent to the room at a common location; in which a return opening may be provided within every supply opening in a room; in which electronics and communications networks are co-located with the ductwork; and in which heating, air conditioning and purification can be performed more efficiently and effectively. 
         [0004]    The present invention fills these and other needs. 
       SUMMARY OF THE INVENTION 
       [0005]    In a first aspect, the present invention provides an apparatus for supplying air to a room in a building and returning air from the room to a motive source of air circulation, comprising: supply ductwork for carrying a flow of supply air from the source to the room; return ductwork for carrying a flow of return air from the room; at least one supply opening in the supply ductwork, said supply opening at an elevation above the floor of the room and laterally inward from the walls of the room for allowing passage of air from the supply ductwork in a downward direction to the room; and at least one return opening in the return ductwork, said return opening at an elevation above the floor of the room and laterally inward from the walls of the room for allowing passage of air from the room in an upward direction to the return ductwork; wherein at least one of said at least one return opening is centrally disposed to at least one of said at least one supply opening so that a flow of supply air and flow of return air will cause an air flow pattern within the room in which supply air flows downward from the supply ductwork and return air flows upward to the return ductwork interior of the downward supply flow. 
         [0006]    In a second aspect, the present invention provides a method of constructing an apparatus for supplying air to a room in a building and returning air from the room to a motive source of air circulation, comprising: connecting a first end of supply air ductwork to the downstream side of the motive source; connecting a first end of return air ductwork to the upstream side of the motive source; merging the supply air ductwork with the return air ductwork so that the return air ductwork is disposed interior to the supply air ductwork downstream of the merger in the direction of the supply flow; and placing a second end of said supply air ductwork in fluid communication with the air in a room; and placing a second end of said return air ductwork in fluid communication with the air in said room interior to the second end of said supply ductwork. 
         [0007]    In a third aspect, the present invention provides a method of providing a flow of circulating air to a room in a building and returning air from the room to the motive source of circulation, comprising: connecting a first end of supply air ductwork to the downstream side of the motive source for circulating air through the system; connecting a first end of return air ductwork to the upstream side of said source; placing a second end of said supply air ductwork in fluid communication with the air in a room at an elevation above the floor of the room and laterally inward from the walls of the room; placing a second end of said return air ductwork in fluid communication with the air in a room interior to the second end of said supply air ductwork at an elevation above the floor of the room and laterally inward from the walls of the room; activating the motive source to draw air from the room upward through the second end of the return ductwork and force air downward through the second end of the supply air ductwork around the second end of the return ductwork. 
         [0008]    In a fourth aspect, the present invention provides a method of circulating air in a room in a building and returning air from the room to the motive source of circulation, comprising: forcing supply air through ductwork into the room through at least one supply opening in the ductwork so as to induce a downward supply current of air in the room below said opening; and concurrently with said forcing step, drawing return air through ductwork out of the room through at least one return opening in the ductwork located centrally to the at least one supply opening so as to induce a return current of air in an upward direction central to the downward supply current. 
         [0009]    In a fifth aspect, the present invention provides a method of converting an existing supply duct of an air circulation system in a building into a dual duct, comprising: providing a return duct of small enough cross section to fit into the existing supply duct; and sliding the return duct inside the supply duct so as to form an annular space between the ducts for carrying a flow of supply air. The method may further comprise connecting the portion of the return duct that is furthest upstream in the supply duct flow direction to the upstream side of the motive source of air circulation. An opening in the supply duct is provided and connecting ductwork is disposed through said opening to connect the return duct and motive source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, may be best understood by reference to the following detailed description of various embodiments and the accompanying drawings in which: 
           [0011]      FIG. 1  is an elevation view of an air circulation system of the present invention. 
           [0012]      FIG. 2  is a perspective view of the air circulation system of  FIG. 1 . 
           [0013]      FIG. 3A  is a side view of a convergence of return and supply ductwork of the present invention. 
           [0014]      FIG. 3B  is a top view of the convergence of  FIG. 3A . 
           [0015]      FIG. 3C  is a close up view of the convergence of  FIG. 3B . 
           [0016]      FIG. 4A  is a perspective view of a compact convergence of the present invention. 
           [0017]      FIG. 4B  is another perspective view of a compact convergence of  FIG. 4A . 
           [0018]      FIG. 4C  is a side view of a compact convergence of  FIG. 4A . 
           [0019]      FIG. 4D  is a bottom view of a compact convergence of  FIG. 4A . 
           [0020]      FIG. 5  is a perspective view of an assembly of a compact convergence of  FIG. 4A  and a diffuser of the present invention. 
           [0021]      FIG. 6  is a cutaway perspective view of a plenum and branch ductwork of the present invention. 
           [0022]      FIG. 7A  is a perspective view of a flow adjuster of the present invention. 
           [0023]      FIG. 7B  is a front view of  FIG. 7A . 
           [0024]      FIG. 7C  is a right side view of  FIG. 7B . 
           [0025]      FIG. 7D  is plan view of a flow adjuster blade of  FIG. 7B . 
           [0026]      FIG. 7E  is a plan view of another flow adjuster blade of  FIG. 7B . 
           [0027]      FIG. 8  is a perspective view of a diffuser of the present invention from the bottom. 
           [0028]      FIG. 9  is a perspective view of the diffuser of  FIG. 8  from the top. 
           [0029]      FIG. 10A  is a perspective view of the diffuser of  FIG. 8  from the bottom with the cover hinged open. 
           [0030]      FIG. 10B  is a perspective view of the diffuser of  FIG. 8  from the top with the cover hinged open. 
           [0031]      FIG. 11  is a perspective view of another diffuser of the present invention from the bottom. 
           [0032]      FIG. 12A  is a perspective view of a wireway of the present invention with an open channel cover. 
           [0033]      FIG. 12B  is an end view of the wireway of  FIG. 12A  with a closed channel cover. 
           [0034]      FIG. 12C  is an end view of the wireway of  FIG. 12A . 
           [0035]      FIG. 13A  is another view of  FIG. 12A . 
           [0036]      FIG. 13B  is a perspective view of an assembly of a wireway and ductwork of the present invention. 
           [0037]      FIG. 14A  is a perspective view of an air sample module of the present invention. 
           [0038]      FIG. 14B  is a close up perspective view of a portion of the air sample module of  FIG. 14A . 
           [0039]      FIG. 14C  is a front view of  FIG. 14A . 
           [0040]      FIG. 14D  is a right side view of  FIG. 14C . 
           [0041]      FIG. 15A  is a perspective view of a roller spacer of the present invention. 
           [0042]      FIG. 15B  is a front view of  FIG. 15A . 
           [0043]      FIG. 16A  is a perspective view of ductwork of the present invention with return ductwork partially inserted in supply ductwork and roller spacers attached to the return ductwork. 
           [0044]      FIG. 16B  is a close up view of a portion of  FIG. 16A . 
           [0045]      FIG. 17A  is a perspective view of a connection between supply ductwork and return ductwork of the present invention. 
           [0046]      FIG. 17B  is a perspective view of a joint between adjacent return ducts of the present invention, with the ducts truncated. 
           [0047]      FIG. 18A  is a perspective view of an assembly of an air handling unit and ductwork of the present invention. 
           [0048]      FIG. 18B  is another perspective view of  FIG. 18A . 
           [0049]      FIG. 19A  is another perspective view of  FIG. 18A . 
           [0050]      FIG. 19B  is a perspective view of an air sample module of the present invention. 
           [0051]      FIG. 19C  is a perspective view of a dump valve of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    The term “downstream” herein means in the direction of the flow of air and “upstream” means in the opposite direction of flow. An “upstream” location is located a distance away from the point of reference in a direction opposite the flow direction. The “upstream side” of an object refers to the side facing the upstream direction. For example, the upstream side of a fan is the air intake side of the fan and the downstream side of a fan is the air exit side of the fan. 
         [0053]    With reference to  FIGS. 1 and 2 , a preferred embodiment of the HVAC system  1  of the present invention may comprise an air handling unit  10 , which unit comprises a motive source of circulation such as a blower  11  ( FIG. 19A ). The downstream side of air handling unit  10  is connected to supply ductwork  40  and the upstream side of the unit is connected to return ductwork  30 . Air handling unit  10  draws air through ductwork  30  and blows the air through supply ductwork. Supply ductwork  40  carries the air to a room, and return ductwork  30  carries air from the room to unit  10 . The supply and return ductwork each have at least one opening into at least one room in the building. In the embodiment shown, the supply and return ductwork merge (see  FIGS. 18A and 18B ) so that the return ductwork is interior to the supply ductwork so that the paths of the two ducts coincide for some distance. The main ductwork may divide into multiple branches, each of which may comprise a return branch  32  within a supply branch  42 . In the embodiment shown, each branch terminates at a vent where supply air is blown into the room and return air is drawn from the room so as to form a downward supply current  4  and upward return current  5  interior of the supply current. Thus is formed an air flow circulation around a continuous path comprising air handling unit  10  connected to supply ductwork  40  connected to room  210  connected to return ductwork  30  connected to air handling unit  10 . 
         [0054]    Air handling unit  10  may be mounted on a roof  201  of the building. 
         [0055]      FIGS. 1 and 2  show an embodiment of the present invention with multiple branches and multiple vents where each branch vents to the room. The branches may branch off from a plenum  43  ( FIG. 6 ). Although six are shown, there may be any number of branches and vents. The vents  3  may be spaced in a regular or irregular pattern and may be spaced in any arrangement as necessary to meet needs and requirements presented under any particular scenario, to accommodate variables such as the characteristics of the air handling unit, size and shape of the room, uses of the room, and desired flow rates. 
         [0056]    The term “vent” in noun form refers to a locus or loci for passage of air, and not necessarily structure except structure expressly recited. A vent may comprise a supply duct opening and a return duct opening at a common location or in close enough proximity so that they may cooperate to promote a local air circulation in the room in which supply air flows downward from the vent and return air flows upward to the vent interior of the supply flow. A vent may comprise a return duct opening centrally located within a return duct opening. 
         [0057]    With reference to  FIGS. 3A-3C , the return ductwork  30  converges with the supply ductwork  40  through an opening in the side of the supply ductwork and is disposed inside the supply ductwork downstream of the convergence in the direction of the supply flow. The circumference of the supply ductwork may expand to accommodate the return ductwork and maintain sufficient flow area. 
         [0058]    With reference to  FIGS. 4A-4D , in another embodiment, the opening in the supply ductwork is formed by a coaxial transition section  44  in which the circumference of the supply ductwork expands and the longitudinal direction of the supply ductwork changes course to conform with the longitudinal direction of the return ductwork. The upstream portion of the transition section is shaped to channel the supply flow to one side of the return flow ductwork. The transition section then transitions the flow into an annular space around the return ductwork. The ducts may converge at any location along the path of the ducts as may be desired, and may diverge and re-converge. 
         [0059]    With reference to  FIG. 5 , the convergence may occur in close proximity to the room and may comprise a transition section connected to the diffuser. For ductwork exposed in the room, the convergence may occur in the room. 
         [0060]    With reference to  FIG. 6 , each branch may be equipped with a flow adjuster  60 . With reference to  FIGS. 7A-7E  showing a preferred embodiment, transverse slits (not shown) may be provided in the supply and return duct walls for slidably receiving blades of flow adjuster  60 . The slits are a sufficient length to accommodate entry of the blades. Flow adjuster  60  may comprise a scabbard  61  attached to branch supply duct  42  for housing one or more slidable blades  63  and  64  that are slidable over a range from an open position to closed position. In the embodiment shown, the flow adjuster comprises a first blade  63  and second blade  64  that are slidable towards each other to close the ducts and away from each other to open the ducts. First blade  63  comprises a rounded front portion  66  conforming to the size and shape of the return duct&#39;s concave interior wall surface, and shoulder edges  67  for contacting the leading edges  68  of second blade  64 . Second blade  64  comprises leading edges  68  and an edge  69  having a concave profile forming a pocket that conforms to the size and shape of the return duct&#39;s convex exterior wall surface. 
         [0061]    With further reference to  FIGS. 7A-7E , blades  63  and  64  are each connected to a motor  62 , which is an electric stepper motor in a preferred embodiment. Motors  62  move the blades over a range of motion from an open position to a closed position. In the open position, the blades are separated from one another and retracted from the ducts. In the closed position, edges  68  of blade  64  contact edges  67  of blade  63 , and concave edge  69  of blade  64  closes against the outside surface of branch return duct  32  to close off the annular passage of branch supply duct  42 ; and convex edge  66  of blade  63  closes against the interior surface of duct  32  to close off the return flow. Flexible membrane seals seal the slits when the blades are retracted and seal the space between the ductwork and blades when the blades are inserted. An opposing seal is attached to the ductwork on either side of each slit. The opposing seals overlap each other so that they cooperate to seal the slits. 
         [0062]    While the ductwork of the preferred embodiment may be round, the ductwork may have other shapes, such as rectangular or other polygonal shapes. Ductwork may transition from one size or shape to another size or shape. Supply ductwork may have different shape than return ductwork. Flow adjuster blades  63  and  64  are provided to conform to the duct shape. 
         [0063]    With reference to  FIGS. 8, 9, 10A and 10B , one embodiment of the present invention comprises a diffuser  100  connected to the ductwork at the fluid interface between the ductwork and the room. The diffuser of  FIG. 8  comprises central return portion  121  and annular supply portion  122  which correspond with central return duct and annular space of the outer supply ductwork. The term “central” does not require concentricity or symmetry between the supply and return ducts or the supply and return portions of the diffuser. For example, a return duct within a supply duct is central to the supply duct even if it is not concentric and does not have the same shape. A return duct and its opening into a room may be considered central to a supply duct and its opening into a room even if the return duct extends beyond the supply duct opening as long as it is within the periphery of the supply duct opening when viewed from directly below. 
         [0064]    With reference to  FIGS. 10A and 10B , diffuser  100  comprises a support  120  for connection to the ductwork and a cover  130  releasably attached to support  120 . With reference to  FIG. 8 , supply portion  122  of cover  130  comprises supply louvers  134  for directing supply air flow outwardly and downwardly from the diffuser. Return portion  121  may comprise a grill  132  with an open lattice framework through which return air is drawn in an upward direction interior to the supply air flow. Supply air is blown and return air is drawn through the ductwork and diffuser of the present invention so as to form an air current comprising a downward supply current  4  ( FIGS. 1 and 2 ) and upward return current  5  ( FIGS. 1 and 2 ) in the room in the vicinity of the diffuser. 
         [0065]    The diffuser may be round as in  FIG. 8 , rectangular as in  FIG. 11 , another shape conforming to the shape of the ductwork, or any other desirable shape. 
         [0066]    The present invention provides many mechanical advantages and improved fluid-dynamic and thermo-dynamic performance over current systems. Coincidence of return and supply duct runs provides for more compact construction and more efficient use of building space. Significantly less insulation material is required to insulate coaxial ducts compared to separate ducts of the same length and flow area. Coincident supply and return openings provides unique adaptability and scalability to meet the needs of various room sizes and shapes. As shown in  FIGS. 1 and 2 , multiple supply/return vents may be dispersed throughout the room, thus creating multiple localized air currents that more efficiently circulate air throughout the room. The dispersal pattern of such vents may be tailored to room size and geometry. Non-uniform dispersal of vents may be used to provide non-uniform flow currents as may be desired for non-uniform needs within a room. Vent elevations above the floor may be variable from vent to vent to adapt to different needs in different regions of the room. Flow adjusters  60  ( FIGS. 6 and 7 ) may be provided and separately controlled to separately control flow velocity and volumes for each branch of a multi-branch system ( FIGS. 1, 2 and 6 ). Thus, the system of the present invention provides improved performance, flexibility, and scalability with fewer resources and greater efficiency than current systems. 
         [0067]    The coincident supply/return vents of the present invention, each providing dual supply and return capacity, provides new HVAC system design flexibility and design methodologies. Systems may be designed in scalable, modular fashion. Design requirements may be achieved by selecting the number and placement of vents having known individual performance profiles and that cooperate together in known and scalable aggregate performance profiles. 
         [0068]    Dispersal of multiple supply/return vents provides more effective and uniform air circulation and reduces or eliminates localized stagnation or inadequate air flows. 
         [0069]    In reference to  FIGS. 12A-13B , the present invention may comprise a wireway  80  that is attachable to the ductwork for carrying various types of circuitry, such as electrical wires and fiber optics. The wireway may run along the ductwork for any distance and in any path. With reference to the preferred embodiment of  FIGS. 12A-12C , wireway  80  may comprise a base  81  with channel troughs  82  extending from the base forming channels for receiving wiring along the length of the wireway. Channel troughs  82  are spaced apart so as to form channel side openings  83  through which wiring may be installed and removed. Wireway  80  may be provided with channel cover  85  hingedly connected to base  81  via hinge  86 , which hinge may be sealed to provide a moisture barrier. Cover  85  comprises a lip  88  for cooperating with lip  89  of the base to form a releasable snap latch connection  87  for releasably covering the channels. The channels may have open ends  84 . Channel troughs  82  may have condensate vents  96  to allow escape and evaporation of condensate from the channels. 
         [0070]    With reference to  FIG. 13A , wireway  80  may carry any variety of circuitry, such as ethernet  90 , audio  91 , multi-conductor  92  (for video surveillance, smoke and fire detector, and motion detector), coaxial cable  93 , fiber optics  94 , and line voltage wire  97 . 
         [0071]    Wireway base  81  may be provided with adhesive strips as means of attachment to the ductwork. Base  81  may be provided with holes for receiving threaded fasteners or other fastener types for attachment to the ductwork. 
         [0072]    The length of the wireway is as long as may be required by the desired application. The wireway may be provided in segments of the same or different lengths attached endwise to form long continuous runs. 
         [0073]    With reference to  FIGS. 8 and 9 , diffuser  100  may comprise an air filter (not shown) disposed in filter location  146  of the return portion  121  of support  120  above grille  132 , said filter for trapping airborne dust. Diffuser may further comprise a pressure sensor  142  or flow rate sensor (not shown) attached to support  120  and disposed above filter location  146  for detecting pressure and pressure changes in the ductwork, such as changes that may be caused by a fouling air filter in location  146 . Diffuser  80  may further comprise one or more of the following types of instrumentation, alone or in combination: room surveillance cameras  137 ; lights  138 ; emergency lighting; indicator lights  143  to signal pressure sensor information; audio speakers  140 ; air quality indicator lights; detectors and alarms for smoke, heat, carbon dioxide, carbon monoxide, and matter and conditions; and motion detectors. 
         [0074]    Pressure sensor  142  in circuit with indicator light  143  may indicate when the air filter in location  146  of the diffuser needs to be changed or serviced. 
         [0075]    The diffuser may comprise circuitry necessary to support the electronic, fiber optic, and other types of equipment and instrumentation and may be adapted for receiving retrofit instrumentation and circuitry. Diffuser  100  may comprise a circuitry connector  144  connected in circuit with diffuser equipment and instrumentation, said connector adapted for releasable connection to external circuitry having a compatible connector. The diffuser may further comprise compatible connector  145  connected in circuit with the circuitry carried in wireway  80 . Connectors  144  and  145  may be pin and socket type connectors or any other suitable connector type. Connectors  144  and  145  may be releasably connected to accommodate repeated disconnection for maintenance and upgrades. 
         [0076]    With reference to  FIGS. 9A-10B , cover  130  is releasably attachable to support  120 . Releasable attachment may be by means of one or more pinned hinge joints comprising a pin  136  releasably inserted into aligned holes in the support and cover. The cover may rotate between open and closed positions about said hinged joint. Cover  130  may be held in the closed position by another releasable pinned joint. Any other suitable means of releasable attachment between the cover and support may be used. 
         [0077]    In the embodiment of  FIGS. 8-11 , cover  130  comprises connector  144  and support comprises compatible connector  145 , which connectors are connected in circuit with one another when the cover is closed, and are disconnected when the cover is opened. 
         [0078]    With reference to  FIGS. 15A-16B , ductwork  30  and  40  may comprise roller spacers  70  for maintaining spacing and alignment of the ductwork  30  and  40  with respect to each other and for facilitating installation of ductwork  30  within ductwork  40 . Roller spacers may comprise a body  71  attached to a ductwork  30  and a wheel  73  rotatably connected to the body with axel  73  and in rolling contact with ductwork  40  at the peripheral wheel surface. In an alternate embodiment, the body may attached to ductwork  40  with the wheel in rolling contact with duct  30 . 
         [0079]      FIG. 16A  shows two sets of roller spacers attached to a rectangular duct  30 , each set spaced apart from one another longitudinally along the duct, and each set comprising a roller at each corner of the rectangle. Any desirable number and spacing of sets may be used, and any desirable number and spacing of rollers within a set may be used as necessary to maintain spacing, stability and ease of insertion of one duct into another. 
         [0080]    Said roller spacers simplify installation of the inner duct with the outer duct. The roller spacers also facilitate a method of introducing a new return duct to convert an existing supply duct into a dual duct. Sliding the new return duct inside the supply duct forms an annular space between the ducts for carrying supply air. The method may further comprise connecting the portion of the return duct that is furthest upstream in the supply duct flow direction to the upstream side of the motive source of air circulation. An opening in the supply duct is provided, and connecting ductwork is disposed through said opening to connect the return duct and motive source. The roller spacers maintain desired spacing for the annular flow area. Other structure may be used to provide the spacing. With the return and supply ducts thus connected to the motive source of circulation and in fluid communication with the room as described elsewhere herein, the existing system may be converted to a system of the present invention to cause air circulation in the room with a downward supply current around an upward return current. 
         [0081]    Roller spacer  70  may comprise body  71  and flanges  72  hinged to the body, said flanges for connecting to ductwork. Body  71  may comprise at least one opening  75  for receiving a wheel axel  74 . Wheel  73  is connected to body  71  via axel  73  inserted in opening  75 . Opening  75  may be an elongated slot disposed at an angle to the hinges so as to provide adjustability in the axel position and overall spacer height as measured from the hinge to peripheral wheel surface. Hinged flanges permit flush attachment of the flanges onto flat surfaces or onto two adjacent surfaces forming a range of angles from acute to obtuse. 
         [0082]    Roller flanges  72  may be provided with adhesive strips  78  for attachment to a duct. Roller body  71  may be provided with a slot  76  for receiving a band so that roller may be attached to a duct with a band clamp clamped around the duct. Roller flanges  72  may comprise tabs  77  forming a guide for receiving a band and stabilizing the roller in desired alignment with the band. 
         [0083]    In the embodiment of  FIG. 16A , ductwork  30  may be slid into ductwork  40  while roller spacers  70  maintain spacing and roll to minimize sliding force. 
         [0084]    With respect to  FIGS. 17A and 17B , suspension coupling  50  of short length and of roughly the same outside diameter as the inside diameter of ductwork  40  may be inserted into the end of ductwork  40  and cinched in place by band clamp  51  around ductwork  40 . Suspension hooks  52  may be connected to and disposed radially inward from suspension coupling  50 . Hooks  52  have a hooked distal end connected to ductwork  30 . 
         [0085]    With reference to  FIG. 17B , an embodiment of the present invention provides return duct couplings  57  and  58  attached to the abutting ends of return duct segments for connecting said segments together endwise. Coupling  57  comprises one or more tabs  55  extending radially outward, which tabs are disposed in one or more corresponding slots  56  of coupling  58 . Slots  56  are formed on a flange  53  of coupling  58 . Assembly comprises attaching the end couplings to a first and second return duct segment, bringing the adjacent ends of the first and second segments together so that tabs  55  abut against flange, and rotating one or both duct segments to dispose tabs  55  into slots  56 . The connection may be releasable by reverse rotation. The couplings may be inserted into the ends of the return duct segments and may have an interference fit with the inside diameters of said segments. Any suitable means of affixation of the couplings to the return duct segments may be used. 
         [0086]    Flange  53  comprises holes  59  for receiving hooks  52 . In the embodiment of  FIG. 17A , hooks  52  comprise four hooks equally spaced apart around the ductwork. Thus, ductwork  30  and  40  are connected together and spaced apart by hooks  52 . 
         [0087]    With reference to  FIGS. 18A, 18B and 19A , air handling unit  10  comprises a blower  11  or other motive source of air circulation (also referred to herein as “circulator”). Supply ductwork  40  is connected to air handling unit  10  on the downstream side of said unit, and return ductwork  30  is connected to the upstream side of the air handling unit. Air handling unit may further comprise one or more dehumidifiers (not shown), electrostatic precipitators  12 , ultraviolet germicidal irradiators  13 , HEPA/MERV filtration modules  14 , and carbon filter modules  15 . In a preferred embodiment, electrostatic precipitators  12  are upstream of circulator  11 , ultraviolet germicidal irradiators  13  are downstream of circulator  11 , HEPA/MERV filtration modules  14  are downstream of the germicidal irradiators  13 , and the carbon filtration modules  15  are downstream of the germicidal irradiators  13 . The various modules may be configured with compatible size, shape and connecting structure so that they may be readily assembled in various combinations and sequences and multiple modules may be stacked in any combination or number. Such modular design also promotes simple and fast replacement and maintenance of modules. 
         [0088]    Electrostatic precipitators  12  may comprise charged aluminum plates for electrostatically precipitating matter out of the air stream, including particulate matter ranging in size from 0.01 to 1 micron. 
         [0089]    Ultraviolet germicidal irradiators  13  may comprise ultraviolet light sources which emit short wave ultraviolet radiation, which is known to kill or disable bacteria, viruses, molds, and other microorganisms and pathogens. 
         [0090]    HEPA/MERV filtration modules  14  comprise a High Efficiency Particulate Arrestance (“HEPA”) filter or an air filters having a Minimum Efficiency Reporting Value (“MERV”) in the range of 13-20, or a combination thereof. HEPA filters remove at least 99.97% of particles that have a size of 0.3 microns from the air passing through the filter. Filters in the MERV 13-20 range are effective at filtering particulate of 1 micron in size and smaller. 
         [0091]    Carbon filter modules  15  comprise activated carbon filters for absorbing odors, vapors and other hydrocarbons and chemicals. 
         [0092]    In a preferred embodiment, HEPA/MERV filtration modules  14  are adjacent to and downstream of germicidal irradiators  13 . In this embodiment, irradiators  13  direct ultraviolet radiation at contaminants in the air flow within the irradiator and at the upstream side of the adjacent HEPA/MERV filters. Contaminants trapped on the filters may be exposed longer to ultraviolet radiation, which enhances the effectiveness of the radiation. 
         [0093]    A fresh air intake  18  may be connected on the upstream side of the air handling unit. Intake  18  may be opened as needed to permit intake of atmospheric air into the circulation as needed. 
         [0094]    With reference to  FIG. 19C , a dump valve  16  may be connected to air handling unit  10  to divert contaminated air out of the building and draw atmospheric air in. In a preferred embodiment, dump valve  16  is connected upstream of blower  11 . Dump valve  16  is of compatible size and shape to fit with the adjacent ductwork or air handling unit components. In a preferred embodiment, dump valve  16  is rectangular with opposing side walls  17  that are hingedly mounted on their upstream side so that they may swing in synchronized fashion from a closed position to an open position. In the closed position, the four walls form a strait rectangular duct having a rectangular flow channel for uninterrupted through-flow. In the opened position, side walls  17  are swung in the same direction to divert the return flow out one side of the dump valve to the atmosphere. In the open position, atmospheric air may be drawn through the other side of the dump valve. In the open position, one side wall  17  is disposed diagonally across the flow channel and the other side wall  17  is disposed outwardly of the flow channel. 
         [0095]    With reference to  FIG. 19B , an air sample module  20  may be connected to air handling unit  10 , preferably to the upstream side of said unit. With reference to  FIGS. 14A-14D , air sample module  20  may comprise at least one sampling reed  21  disposed across the air flow in the module. Sampling reed  21  is hollow with a wall forming an interior chamber, and at least one sampling port  24  through said wall. Port  24  is exposed to the air flow to pass samples into chamber  23 . Air sample tube  25  is connected to said reeds to transport samples away for analysis. 
         [0096]    The improved capability of the present invention to monitor and to sustain high quality of interior air permits more recirculation of interior air and less introduction atmospheric makeup air. Thus, significant energy expenditures to heat or cool makeup air may be saved. 
         [0097]    While the invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the invention without departing from the spirit and scope of the invention as described in the following claims