Patent Publication Number: US-10788236-B2

Title: Air diffusion

Description:
FIELD OF THE INVENTION 
     This invention relates to air diffusers for use in air conditioning systems. 
     BACKGROUND TO THE INVENTION 
     Air diffusers are used to reduce velocity and increase static pressure of air as it is distributed from a heating, ventilation and air conditioning (HVAC) system to a space such as an air-conditioned room. (The space targeted by an HVAC system is referred to as a “room” herein, for the sake of brevity, but the space can take any other form.) 
     Variable volume air diffusers can regulate the flow-rate of air distributed to the room and the flow-rate can be adjusted manually or automatically, to achieve desired ventilation and/or temperature conditioning. 
     Many HVAC systems can operate in a “heating mode”, to supply hot air to the room, or in a “cooling mode” to supply cold air to the room and the room temperature can be controlled by controlling the volumetric flow of air through a diffuser. 
     Further to these functions, air diffusers are also often used to distribute air evenly in desired directions as it enters the room—especially to cause a jet of air from the diffuser to attach to a ceiling, taking advantage of the Coand{hacek over (a)} effect. However, in some instances, it would be desirable to depart from these benefits imparted on the HVAC air supply by the diffuser. In particular, in some instances it may be desirable for air from the HVAC system to flow downwardly into a room. One example is when a cold room needs to be heated rapidly, despite the tendency of hot air to rise. A conventional diffuser would cause hot air from the HVAC system to be accumulate immediately below the ceiling and only gradually to fill the room. 
     The present invention seeks to provide for selective supply of air to a room with air diffusion, or with air-flow that flows directly into the room with reduced or no diffusion. 
     The invention seeks to provide said selective supply of air in a cost effective manner, while allowing volumetric control of air flow. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided an air diffuser comprising:
         a body defining at least one control flow passage;   a volume control mechanism including at least one movable element that is displaceable relative to the body, to adjust the size of the control flow passage;   said body defining at least one diffusion flow passage that is in communication with the control flow passage and that is configured to direct flow from the control flow passage in a first diffusion direction; and   a dump mechanism comprising at least one dump element that is displaceable between a first diffusion position in which the diffusion flow passage is directed in the first diffusion direction, and a second diffusion position in which the dump element redirects the diffusion flow passage to deviate from the first diffusion direction.       

     The second diffusion position of the dump element may be within the diffusion flow passage. 
     The first diffusion position may be a retracted position in which the dump element is substantially clear from the diffusion flow passage and the second diffusion position may be an extended position in which the dump element protrudes at least partly into the diffusion flow passage. The dump element may be retracted into the body in the first diffusion position and may protrude from the body in the second diffusion position. 
     The dump element may be disposed inside the diffuser body and may be pivotally supported to pivot between its first diffusion position and its second diffusion position. 
     The dump element may close a second flow passage at least in part, and restrict a flow of air to the diffusion flow passage when the dump element is in the first diffusion position, and may open the second flow passage and permit the flow of air to deviate, at least in part, from the diffusion flow passage to the second flow passage when the dump element is in the second diffusion position. 
     The dump mechanism may include a dump actuator that is configured to displace the dump element between the first diffusion position and the second diffusion position and the dump element may be biased to the first diffusion position.
         According to another aspect of the present invention there is provided a method of controlling a flow of air through a diffuser, said method comprising:   supplying a flow of air to a diffuser;   directing the flow of air through a control flow passage;   controlling the volumetric flow rate of the flow of air;   directing the flow of air through a diffusion flow passage;   directing the flow of air from the diffusion flow passage in a first diffusion direction;   selectively operating a dump mechanism to displace a dump element from a first diffusion position in which the flow of air is directed in the first diffusion direction, to a second diffusion position in which the dump element redirects the flow of air to deviate from the first diffusion direction.       

     The first diffusion direction may extend in the proximity of a ceiling and the step of operating the dump mechanism may include displacing the dump element to the second diffusion position to redirect the flow of air away from the ceiling. 
     The method may include controlling the volumetric flow rate while the flow of air is deviated from the first diffusion direction by the dump element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, and to show how it may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which: 
         FIG. 1  shows a top three-dimensional view of a first embodiment of an air diffuser according to the present invention; 
         FIG. 2  shows a side view of the diffuser of  FIG. 1 ; 
         FIG. 3  shows a top view of the diffuser of  FIG. 1 ; 
         FIG. 4  shows a detail top view of a support assembly of the diffuser of  FIG. 1 ; 
         FIG. 5  shows a sectional view of the support assembly of  FIG. 4 , taken at V-V; 
         FIG. 6  shows a top view of a dump mechanism of a second embodiment of an air diffuser according to the present invention, in a first diffusion condition; 
         FIG. 7  shows a sectional side view of a the second embodiment of an air diffuser according to the present invention, in the first diffusion condition; 
         FIG. 8  shows a top view of the dump mechanism of  FIG. 6 , in a second diffusion (dumping) condition; 
         FIG. 9  shows a sectional side view of a the diffuser of  FIG. 7 , in the second diffusion (dumping) condition; 
         FIG. 10  shows a three-dimensional top view of a third embodiment of an air diffuser according to the present invention; 
         FIG. 11  shows a three-dimensional top view of a volume control mechanism and dump mechanism of the diffuser of  FIG. 10 ; 
         FIG. 12  shows a sectional side view of the diffuser of  FIG. 10 , in a first diffusion condition; 
         FIG. 13  shows a sectional side view of the diffuser of  FIG. 10 , in a second diffusion (dumping) condition; 
         FIG. 14  shows a three-dimensional bottom view of a fourth embodiment of an air diffuser according to the present invention; 
         FIG. 15  shows a three-dimensional top view of a volume control mechanism and dump mechanism of the diffuser of  FIG. 14 ; 
         FIG. 16  shows a sectional side view of the diffuser of  FIG. 14 , in a first diffusion condition, with its volume control open; 
         FIG. 17  shows a sectional side view of the diffuser of  FIG. 14 , in a first diffusion condition, with its volume control closed; 
         FIG. 18  shows a sectional side view of the diffuser of  FIG. 14 , in a second diffusion (dumping) condition; 
         FIG. 19  shows a three-dimensional top view of a blade sub-assembly of a fifth embodiment of an air diffuser according to the present invention, including a detail view; 
         FIG. 20  shows a sectional side view of the diffuser of  FIG. 19 , in a first diffusion condition, with its volume control open; 
         FIG. 21  shows a sectional side view of the diffuser of  FIG. 19 , in a first diffusion condition, with its volume control closed; 
         FIG. 22  shows a sectional side view of the diffuser of  FIG. 19 , in a second diffusion (dumping) condition; 
         FIG. 23  shows a top three-dimensional view of a sixth embodiment of an air diffuser according to the present invention; 
         FIG. 24  shows a top three-dimensional view of a dump mechanism of the diffuser of  FIG. 23 ; 
         FIG. 25  shows a sectional view of the diffuser of  FIG. 23  with dump elements in their diffuser positions; 
         FIG. 26  shows a sectional view of the diffuser of  FIG. 23  with dump elements in their second diffusion positions; 
         FIG. 27  shows a top three-dimensional view of a dump mechanism of a seventh embodiment of an air diffuser according to the present invention; 
         FIG. 28  shows a sectional view of the diffuser of  FIG. 27  with dump elements in their diffuser positions; and 
         FIG. 29  shows a sectional view of the diffuser of  FIG. 27  with dump elements in their second diffusion positions. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings, an air diffuser in accordance with the present invention is generally indicated by reference numeral  10 . Features that are common between different embodiments of diffusers according to the invention are identified by the same reference numbers and where applicable, different embodiments of the diffusers or features are identified by suffixes. 
     Referring to  FIGS. 1 to 5 , the air diffuser  10 . 1  includes a body in the form of a casing  12  that is configured to be supported as part of a suspended ceiling, receiving air from an HVAC system above the ceiling. The casing  12  defines an internal control flow passage that extends from a central inlet  14 , which forms a truncated cylindrical neck at the top of the casing, downwards to an outlet on the underside of the casing (not visible in the drawings). The outlet is typically defined around the periphery of a central trim plate (not visible in the drawings), which is generally flush with the underside of the casing. 
     The diffuser  10 . 1  includes a volume control mechanism that includes a movable element such as a baffle or control disc (not visible in the drawings) that is displaceable inside the casing  12  to increase or decrease the size of the control flow passage, to control the flow of air from the HVAC system, that flows from the inlet  14  and is discharged to the room below, through the outlet of the diffuser  10 . 1 . 
     On the underside of the casing  12 , the diffuser  10 . 1  defines a diffusion flow passage, which extends from the outlet (around the periphery of the trim plate), outwards in a first diffusion direction along the underside of the casing. Air that exits the diffuser  10 . 1  along this diffusion flow passage would tend to continue flowing outwards beyond the periphery of the diffuser, along the underside of an adjacent ceiling, by operation of the Coand{hacek over (a)} effect. 
     Above each corner of the casing  12 , a support mechanism  16  is provided, which includes a base  18  that is attached to the casing and a hanger  20  that is supported above the base. The base  18  has an upstanding hollow pin  22  on which the hanger  20  is received and the hanger is supported by a compression helical spring (not shown) that extends between the pin and the hanger. A passage  24  is defined inside the base  18  and pin  22 , along which a cable (not shown) can extend to be attached to the hanger  20 , so that tension on the cable would pull the hanger downwards relative to the base  18 , against the upward bias of the spring. 
     Cables that extend to each of the four support mechanisms  16  are connected together to form a harness that is connected to a dump actuator in the form of a stepper motor  26 . 1 , so that rotation of the stepper motor causes a cable from the harness to be wound around a pulley and to apply tension to the entire harness. Tension in the harness is transferred to the cables in the passages  24  of each of the support assemblies  16  and causes them to pull the hangers  20  downwards, simultaneously. 
     Four dump elements in the form of narrow blades  28 . 1  are each supported at their opposing ends, by two of the hangers  20 . The stepper motor  26 . 1 , harness of cables, hangers  20  and blades  28 . 1  operate as a dump mechanism, such that the blades move up and down in unison with the hangers, when the stepper motor  26 . 1  applies tension to the cable harness. 
     The casing  12  defines four slots along its periphery and each of the blades  28 . 1  is configured to slide vertically in its associated slot between a retracted or first diffusion position, in which each blade is substantially above the underside of the casing  12 , and an extended or second diffusion position in which most of each blade protrudes below the underside of the casing, as shown in  FIG. 2 . 
     During normal operation of the diffuser  10 . 1 , the cable harness is not under tension and the springs bias the hangers  20  and blades  28 . 1  upwards, so that the blades are in their retracted positions, in which they are clear of the diffusion flow passage and allow the air in the diffusion flow passage to flow in the first diffusion direction, outwardly from the underside of the casing  12  and along the underside of the adjacent ceiling. The diffuser  10 . 1  operates in this condition, in a conventional manner, with volumetric control of the air flow-rate and with diffusion of the air. 
     In the event that a downward flow of air from the diffuser  10 . 1  is required, the stepper motor  26 . 1  is operated to pull the cable harness and to pull the hangers  20  and blades  28 . 1  downwards into their extended positions, with the blades protruding below the underside of the casing  12 , along the periphery of the casing. The lower edges of the blades  28 . 1  protrude into the diffusion flow passage and disrupts the outward flow of air along the undersides of the casing  12  and ceiling and instead, redirects the air to deviate from the first diffusion direction and to flow downwards in a second diffusion direction. 
     The redirection of the air flow by the blades  28 . 1  in their extended positions, is enhanced by rib formations  30  along the bottom edges of the blades. In the embodiment illustrated in  FIGS. 1 to 5 , the rib formations  30  extend continuously along the entire lower edge of each blade  28 . 1 , while the upper part of the blade is discontinuous and defines two gaps  32 . 
     When the downward (dumping) flow of air is no longer required, the stepper motor  26 . 1  is operated to relieve tension on the cable harness and the bias in the springs causes the hangers  20  to lift and to retract the blades into their retracted positions—substantially retracted into the underside of the casing  12 . 
     Referring to  FIGS. 6 to 9 , the second embodiment of a diffuser  10 . 2  according to the present invention includes a casing  12  with an inlet  14 , where it receives a supply of air from an HVAC system. At the bottom of the casing, a fixed central trim plate  34 . 2  is supported generally flush with the underside of the casing and with the adjacent ceiling, with an outlet  36  defined around the circumference of the trim plate. A control disc (not shown) can be supported inside the casing  12 , above the trim plate  34  and form part of a volume control mechanism of the diffuser  10 . 2 , the trim plate being moveable up and down inside the casing to adjust the size of the control flow passage that extends from the inlet  14  to the circumference of the control disc. Instead, the diffuser  10 . 2  could include a rotating control disc  40 . 2  inside the casing  12 , below the inlet  14 , which rotates to adjust the size of the flow passage by varying the extent to which apertures in a fixed plate and in the control disc, overlap. 
     At the outlet  36 , the diffuser  10 . 2  defines a diffusion flow passage, which extends from the circumference of the control disc and trim plate  34 . 2 , outwards in a first diffusion direction along the underside of the casing. Air that exits the diffuser  10 . 2  along this diffusion flow passage would tend to continue flowing outwards beyond the periphery of the diffuser, along the underside of an adjacent ceiling, by operation of the Coand{hacek over (a)} effect, as shown in  FIG. 7 . 
     The diffuser  10 . 2  includes a dump mechanism comprising four dump elements in the form of blades  28 . 2  that are each supported transversely at the end of a bar  38 . The dump mechanism includes an actuator in the form of stepper motor  26 . 2  with a pinion (not shown) that meshes with linear gear teeth on each of the bars  38  in rack-and-pinion fashion, so that rotation of the stepper motor drives each of the bars  38  to travel longitudinally inwards or outwards, simultaneously, in directions oriented at right angles relative to one another. 
     During normal operation of the diffuser  10 . 2 , the blades  28 . 2  are in first diffusion positions or retracted positions as shown in  FIGS. 6 and 7 , in which they are retracted behind the trim plate  34 . 2  and are substantially clear of the diffusion flow passage, so that they allow the air in the diffusion flow passage to flow in the first diffusion direction, outwardly from the underside of the casing  12  and along the underside of the adjacent ceiling, as shown in  FIGS. 6  an  7 . The diffuser  10 . 2  operates in this condition, in a conventional manner, with volumetric control of the air flow-rate by operation of the control disc  40 . 2 , and with diffusion of the air. 
     In the event that a downward flow of air from the diffuser  10 . 2  is required, the stepper motor  26 . 2  is operated to push the bars  38  outwards and push the blades  28 . 2  outwards into second diffusion or extended positions in which the blades protrude beyond the periphery of the trim plate  34 . 2 , as shown in  FIGS. 8 and 9 . The blades  28 . 2  protrude into the diffusion flow passage and disrupts the outward flow of air as it exits the outlet  36  and redirects the air to deviate from the first diffusion direction and to flow downwards in a second diffusion direction, as shown in  FIGS. 8 and 9 . 
     While the diffuser  10 . 2  is in this second diffusion or dumping condition, the volumetric control of airflow-rate continues in the conventional manner by operation of the control disc  40 . 2 . 
     Once the need for downward flow or air from the diffuser  10 . 2  ceases, the stepper motor  26 . 2  is operated to draw the bars  38  and the blades  28 . 2  inwards to return the blades to their retracted positions as shown in  FIGS. 6 and 7 , and normal operation of the diffuser  10 . 2  can resume. 
     Referring to  FIGS. 10 to 13 , the third embodiment of a diffuser  10 . 3  according to the present invention includes some features that are very similar to those of the second embodiment, shown in  FIGS. 6 to 9 , including: a casing  12  with an inlet  14 , a volume control mechanism including a rotating control disc  40 . 3 , an outlet  36  around a trim plate  34 . 3  (although the trim plate is quite different—see below), where the diffuser  10 . 3  defines a diffusion flow passage, which extends from the circumference of the trim plate  34 . 3 , outwards in a first diffusion direction along the underside of the casing. An internal casing  42  is also shown in  FIGS. 10 to 13 , which supports the control disc  40 . 3 , with windows  44  in the internal casing, through which air can flow. 
       FIGS. 10 and 11  shows the volume control mechanism of the diffuser  10 . 3 , in which the control disc  40 . 3  is in register with a stationary plate in an open condition, with apertures defined in the control disc and the stationary plate, in register. Each aperture is almost twice the width of the adjacent solid part of the control disc  40 . 3  and an intermediary disc (not visible) is provided between the control disc and stationary disc, which is shaped similarly to the control disc and stationary disc. When the control disc  40 . 3  rotates to a closed position, the intermediate disc rotates with it for a part of the rotation, so that the apertures in the stationary plate are partly closed by the control disc and partly by the intermediary disc. 
     The diffuser  10 . 3  includes a dump mechanism comprising a perforated trim plate  34 . 3  and an array of blades  28 . 3  that extend in a radial arrangement above the trim plate. Each of the blades  28 . 3  is pivotally supported above the trim plate  34 . 3  to pivot between a first or closed position in which the blades lie flat against the trim plate in a side-by-side arrangement, blocking the perforations in the trim plate as shown in  FIGS. 10 and 12 , and a second or open position in which the blades extend upwards and do not obstruct the perforations of the trim plate, as shown in  FIGS. 11 and 13 . The dump mechanism includes an actuator in the form of stepper motor (not shown) that is configured to pivot the blades  28 . 3  in unison between their open and closed positions. 
     During normal operation of the diffuser  10 . 3 , the blades  28 . 3  are in their closed positions as shown in  FIGS. 10 and 12 , in which they obstruct the perforations in the trim plate  34 . 3 , so that air flows in the diffusion flow passage in the first diffusion direction, outwardly from the underside of the casing  12  and along the underside of the adjacent ceiling, as shown in  FIG. 12 . The diffuser  10 . 3  operates in this condition, in a conventional manner, with volumetric control of the air flow-rate by operation of the control disc  40 . 3 , and with diffusion of the air. 
     In the event that a downward flow of air from the diffuser  10 . 3  is required, the stepper motor is operated to pivot the blades  28 . 3  upwards to their open positions as shown in  FIGS. 11 and 13 . The apertures in the trim plate  34 . 3  are thus no longer obstructed by the blades  28 . 3  and the outward flow of air as it exits the outlet  36  is disrupted, at least in part, because the air is redirected by the blades to deviate from the first diffusion direction and to flow downwards in a second diffusion direction, through the perforations of the trim plate, as shown in  FIG. 13 . 
     While the diffuser  10 . 3  is in this second diffusion or dumping condition, the volumetric control of airflow-rate continues in the conventional manner by operation of the control disc  40 . 3 . 
     Once the need for downward flow or air from the diffuser  10 . 3  ceases, the stepper motor is operated to pivot the blades  28 . 3  downwards to return them to their closed positions as shown in  FIGS. 10 and 12 , and normal operation of the diffuser  10 . 3  can resume. 
     Referring to  FIGS. 14 to 18 , the fourth embodiment of a diffuser  10 . 4  according to the present invention includes some features that are very similar to those of the third embodiment shown in  FIGS. 10 to 13 , such as: a casing  12  with an inlet  14 , a perforated trim plate  34 . 4  and an outlet  36  around a trim plate, where the diffuser  10 . 4  defines a diffusion flow passage, which extends from the circumference of the trim plate, outwards in a first diffusion direction along the underside of the casing. 
     The diffuser  10 . 4  also includes a volume control mechanism comprising a control disc  40 . 4  that is moved up and down inside the casing  12  in the control flow passage, between that inlet  14  and the trim plate  34 . 4 , to control the size of the flow passage and thus control the volume of air flow through the diffuser. 
     As best seen in  FIG. 15 , the control disc  40 . 4  also includes a dump mechanism comprising a dump disc  46  that is rotatable relative to the control disc. Each of the control disc  40 . 4  and dump disc  46  defines apertures in them and the dump disc can rotate between a first or closed position in which the apertures of the control disc are closed by the dump disc, and a second or open position in which the apertures of the control disc and dump disc are in register and are open. The dump mechanism includes an actuator in the form of stepper motor (not shown) that is configured to rotate the dump disc  46  relative to the control disc  40 . 4 . 
     During normal operation of the diffuser  10 . 4 , the dump disc  46  is in its closed position as shown in  FIGS. 16 and 17 , in which it obstructs the apertures in the control disc  40 . 4 , so that air flows in the diffusion flow passage in the first diffusion direction, outwardly from the underside of the casing  12  and along the underside of the adjacent ceiling, as shown in  FIG. 16 . The diffuser  10 . 4  operates in this condition, in a conventional manner, with diffusion of the air and with volumetric control of the air flow-rate by operation of the control disc  40 . 4 , which moves between an open position as shown in  FIG. 16 , where air passes between the casing  12  and the circumference of the control disc, and a closed position as shown in  FIG. 17 , in which the circumference of the control disc seals against the casing  12 . 
     In the event that a downward flow of air from the diffuser  10 . 4  is required, the control disc  40 . 4  is moved upwards to its closed position and the dump disc  46  is rotated to open the apertures in the control disc and allow air to flow downward through these apertures, as shown in  FIG. 18 . The air is thus no longer only directed to a gap between the circumference of the control disc  40 . 4  and the casing  12  and to flow outwards through the outlet  36  in a first diffusion direction, but a large part of this flow is disrupted and the air is redirected to flow downwards in a second diffusion direction, through the apertures in the control disc and through the perforations of the trim plate  34 . 4 . 
     While the diffuser  10 . 4  is in this second diffusion or dumping condition, the volumetric control of air flow-rate is achieved by controlled rotation of the dump disc  46  in relation to the control disc  40 . 4 , to regulate the degree by which the apertures in these two discs overlap. 
     Once the need for downward flow or air from the diffuser  10 . 4  ceases, the dump disc  46  is rotated to return to its closed positions as shown in  FIGS. 16 and 17 , and normal operation of the diffuser  10 . 4  can resume. 
     Referring to  FIGS. 19 to 22 , the fifth embodiment of a diffuser  10 . 5  according to the present invention includes a casing  12 . 5  that differs somewhat from the first four embodiments, although it also has an inlet  14  or neck at its top and at its bottom, the casing defines an outlet  36 . 5  that is partially closed by a blade sub-assembly  48 . 
     The blade sub-assembly  48  includes a base plate  50  that extends across the outlet  36 . 5  of the casing  12 . 5  and that is typically installed generally aligned with the ceiling. An array of radial outlet apertures  52  are defined in the base plate  50  in a radial pattern and an array of blades  28 . 5  are pivotally mounted on the base plate and are each pivotable between a closed condition in which each blade closes its associated outlet aperture as shown in  FIG. 21 , an intermediate position in which each blade extends at an acute angle relative to the base plate and its associated outlet aperture is open as shown in  FIG. 20 , and a fully open position in which each blade extends generally upright relative to the base plate and its associated outlet aperture is open, as shown in  FIG. 22 . 
     Each of the blades  28 . 5  is attached to a central disc  54  by a crank arm  56 , so that up-and-down movement of the central disc pivots all the blades in unison, in crank-fashion between their closed, intermediate and open positions. Up and down movement of the central disc  54  is affected by operation of a stepper motor (not shown). 
     The diffuser  10 . 5  includes a volume control mechanism and a dump mechanism, but both these mechanisms comprise of the same equipment, operated in different modes. The stepper motor, central disc  54 , crank arms  56 , blades  28 . 5  and base plate  50  with its apertures  52 , make up the volume control mechanism and the dump mechanism. 
     During normal operation of the diffuser  10 . 5 , the volume control mechanism is operated to pivot each of the blades  28 . 5  between its closed position as shown in  FIG. 21  and an intermediate position, e.g. the position shown in  FIG. 20 . The pivoting movement of each blade  28 . 5  in relation to its associated aperture  52  opens and closes the aperture to restrict and thus control the volumetric flow rate of air through the aperture. The angle of each blade  28 . 5  relative to the base plate  50  is at a small enough angle for the flow passage along the blade and through its aperture  52  to serve as a diffusion flow passage and for air to leave the aperture in a first diffusion direction and to travel along the underside of the ceiling, as shown in  FIG. 20 . 
     In the event that a downward flow of air from the diffuser  10 . 5  is required, the central disc  54  is lifted further off the base plate  50  so that the blades  28 . 5  deflect the air flow so that it no longer travels along the ceiling in the first diffusion direction, but air is redirected to flow downwards in a second diffusion direction. 
     Once the need for downward flow or air from the diffuser  10 . 5  ceases, central disc  54  is lowered again to pivot the blades  28 . 5  back to their normal operating positions between their close and intermediate positions, so that normal operation of the diffuser  10 . 5  can resume. 
     Referring to  FIGS. 23 to 26 , the sixth embodiment of an air diffuser  10 . 6  includes a body in the form of an elongate, rectangular casing  64  with a bottom flange  66  that can be integrated in a ceiling. The top of the casing  64  is open and can receive air from an HVAC system—typically from a box that extends upwards above the casing, but possibly also from a plenum. The inside of the casing  64  forms a control flow passage in which air from the HVAC system flows downwards through outlets  68  on the underside of the casing, into a room below. 
     The diffuser  10 . 6  includes a volume control mechanism in the form of a volume control actuator  70  that is configured to slide a moveable element with a series of vanes  72  in relation to stationary vanes (not visible in the drawings) that form part of the casing  64 , to adjust the size of the control flow passage, by adjusting control apertures  74  defined between the movable vanes  72  and the stationary vanes. 
     Below the volume control mechanism, the casing  64  defines a diffusion flow passage, extending from the volume control mechanism, inside the casing and into the room below, through the outlets  68 . The casing  64  includes rounded lips  76  that extend along lateral edges of the outlets  68  and two blades  78  are provided inside the casing  64 , immediately above the outlets. The blades  78  are normally slanted as shown in  FIG. 25 , so that air flowing downward in the diffusion flow passage, is directed to flow downwards around the lower edges of the blades and is urged by the lips  76  to exit the outlets  68  in a first diffusion direction that extends generally along the underside of the flange  66 —as shown by arrows in  FIG. 25 . 
     The blades  78  also serve as dump elements of a dump mechanism, which includes a dump actuator  80  in the form of a stepper motot that is configured to pivot the blades via a connecting bracket  82  between the slanted, first diffusion position shown in  FIG. 25  and a vertical, second diffusion position, shown in  FIG. 26 . 
     During normal operation of the diffuser  10 . 6 , the blades  78  are kept in their first diffusion position and the air leaves the diffuser in the first diffusion direction, along the underside of the adjacent ceiling as shown in  FIG. 25 . However, if a downward flow of air is required, e.g. if rapid heating of a cold room is required, or if the diffuser is required to provide an air curtain or provide heating immediately inside a cold window, then the dump actuator  80  operates to pivot the blades  78  to the second diffusion position shown in  FIG. 26 . The blades  78  redirect the air to deviate from the horizontal first diffusion direction and to flow downwards into the room in a second diffusion direction. 
     To cease downward dumping of air, the dump actuator  80  simply pivots the blades  78  to return them to their slanted first diffusion positions. 
     Referring to  FIGS. 27 to 29 , the seventh embodiment of an air diffuser according to the present invention is substantially similar to the sixth embodiment shown in  FIGS. 23 to 26 , except that the dump actuator is not connected to the blades  78  via a bracket, but instead, the dump mechanism includes a dump actuator  80 . 7  in the form of a stepper motor with a shaft that is directly connected to one of the blades  78  to serve as pivot axle for the blade and upper edges of the blades are connected with a link  84  to link the blades to pivot together. 
     The operation of the diffuser of the seventh embodiment is also practically the same as the sixth embodiment, with the blades  78  being slanted during normal operation and air being directed by the lips  76  to exit the outlets  68  in a first diffusion direction, along the ceiling, as shown in  FIG. 28 , and the blades being pivoted upwards when dumping is required, to direct the air flow downwards in a second diffusion direction as shown in  FIG. 29 .