Abstract:
A variable air volume ceiling diffuser includes a damper that is raised and lowered by a linkage that is controlled by a duct temperature sensor/actuator and one or more room temperature sensors/actuators. The linkage includes a heating slide movable for the heating mode and a cooling slide movable for the cooling mode. The duct temperature sensor/actuator selects the heating slide for movement by the room temperature sensors/actuators in the heating mode and selects the cooling slide for movement by the room temperature sensors/actuators in the cooling mode. The differential movement between the heating and cooling slides moves a roller that engages a profiled cam surface attached to two lever arms. As the roller moves along the cam surface, the lever arms pivot about their axis of rotation so that the damper moves upward to close the air inlet and downward to open the air inlet.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 60/676,697, filed in of the United States Patent and Trademark Office on Apr. 29, 2005, the disclosure of which is hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   This invention relates to variable air volume (VAV) ceiling diffusers and more particularly to a thermally powered VAV ceiling diffuser. 
   BACKGROUND OF THE INVENTION 
   Thermal powered VAV ceiling diffusers are widely used in HVAC systems to control the temperature within an occupied space. The VAV ceiling diffuser is connected to a heating and cooling duct of the HVAC system. The heating and cooling duct supplies either warm or cool air to the diffuser. The diffuser has thermal sensors/actuators that sense the temperature of the air supplied in the duct and the temperature of the occupied space. Based on the sensed temperatures, the thermal sensors/actuators drive a linkage that opens and closes a damper to increase or decrease the amount of heating or cooling air supplied to the occupied space in order to maintain a relatively constant temperature in the occupied space. 
   The prior art discloses a number of thermal powered VAV ceiling diffusers that employ various linkages for controlling the movement of the damper in response to the duct temperature and the room temperature. Because the sensors/actuators provide limited movement, the linkages must be able to translate that limited movement into accurate positioning for the damper in order to control the temperature in the occupied space. 
   SUMMARY OF THE INVENTION 
   In order to control the temperature within the occupied space accurately, the thermal powered VAV ceiling diffuser of the present invention incorporates a number of features that enhance the accuracy of the temperature control. The ceiling diffuser of the present invention is mounted in the ceiling of the occupied space and is connected to an HVAC duct that supplies warm or cool air to the inlet of the diffuser. The diffuser controls the temperature within the occupied space by controlling the amount of heating or cooling air passing through the inlet and into the occupied space from the HVAC duct. The diffuser includes a diffuser hood from which a base plate is suspended. The diffuser has a circular damper stack mounted on the base plate of the diffuser and a damper with a circular opening that slides vertically on the damper stack between an upper closed inlet position and a lower open inlet position. The damper is raised and lowered by a linkage that is controlled by a duct temperature sensor/actuator and one or more room temperature sensors/actuators. 
   The linkage includes two horizontal slides, a heating slide movable for the heating mode and a cooling slide movable for the cooling mode. The horizontal movements of the heating and cooling slides are controlled by the duct temperature sensor/actuator and the one or more room temperature sensors/actuators. The differential movement between the heating and cooling slides moves a roller that engages a profiled cam surface attached to two lever arms. One end of each of the lever arms is pivotally mounted at one end of the base plate for rotation about an axis, and the other end of each of the lever arms engages the bottom of the damper. As the roller moves along the cam surface, the lever arms pivot about their axis of rotation so that the damper moves upward to close the air inlet and downward to open the air inlet. 
   By reducing the friction in the linkage and the loading on the linkage, temperature control accuracy is enhanced. In order to reduce the load on the linkage required to move the damper up and down, the lever arms are spring loaded to offset the weight of the damper. In addition, in one embodiment of the invention, the damper stack and the opening in the damper are circular so that the damper can rotate about the damper stack thereby reducing binding between the damper stack and the damper. Temperature control accuracy is further enhanced by means of the roller and profiled cam surface that together accurately translate the differential sliding movement of the heating and cooling slides into an accurate rotational movement of the lever arms. 
   In operation, the duct temperature sensor/actuator senses the temperature of the air in the duct and activates the heating mode slide when the duct temperature is warm and activates the cooling mode slide when the duct temperature is cool. In the heating mode, the duct temperature sensor/actuator holds the cooling slide stationery while the two room temperature sensors/actuators control the movement of the heating slide by means of a heating set point knob attached to the two room temperature sensors/actuators. The differential movement between the stationary cooling slide and the movable heating slide controls the roller that engages the profiled cam surface attached to the two lever arms. The movement of the two lever arms raises and lowers the damper to control the flow of warm air through the diffuser. 
   In the cooling mode, the duct temperature sensor/actuator holds the heating slide stationery while the two room temperature sensors/actuators control the movement of the cooling slide by means of a cooling set point knob attached to the two room temperature sensors/actuators. The differential movement between the stationary heating slide and the movable cooling slide controls the roller that engages the profiled cam surface attached to the two lever arms. The movement of the two lever arms raises and lowers the damper to control the flow of cool air through the diffuser. The set point knobs are independently adjustable to set the heating temperature and the cooling temperature in the occupied space. 
   The diffuser of the present invention further has a single means for setting the minimum flow rate as well as setting the fully open damper position for HVAC system balancing. Raising and lowering the axis of rotation of the lever arms controls the minimum flow rate and the fully opened position of the damper. 
   In order to gain access to adjust the minimum flow rate, the fully open damper position, and the heating and cooling set points, the diffuser has a plaque that is hinged on one side to the base plate so that the plaque can swing away from the base plate of the diffuser. The other side of the plaque is latched to the base plate by means of rare earth magnets that hold the plaque in its closed position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of the variable air volume ceiling diffuser with a movable damper in accordance with the present invention. 
       FIG. 2  is a top plan view of the diffuser backing hood of the variable air volume ceiling diffuser in accordance with the present invention. 
       FIG. 3  is a side elevation view of the variable air volume ceiling diffuser with a movable damper in accordance with the present invention. 
       FIG. 4  is a detailed view of the base plate hangers and hanger locks of the variable air volume ceiling diffuser in accordance with the present invention. 
       FIG. 5  is an end elevation view of the variable air volume ceiling diffuser and showing the fully open and minimum air adjustment mechanism in accordance with the present invention. 
       FIG. 6   a  is a plan view of the linkage of the variable air volume ceiling diffuser in the heating mode with the damper closed in accordance with the present invention. 
       FIG. 6   b  is a plan view of the linkage of the variable air volume ceiling diffuser in the cooling mode with the damper closed in accordance with the present invention. 
       FIG. 7   a  is a section view of the ceiling diffuser taken along section line  7 - 7  of  FIG. 1  and showing the linkage for controlling movement of the damper (heating mode, damper closed) in accordance with the present invention. 
       FIG. 7   b  is a section view of the ceiling diffuser taken along section line  7 - 7  of  FIG. 1  and showing the linkage for controlling movement of the damper (cooling mode, damper closed) in accordance with the present invention. 
       FIG. 8   a  is a detailed plan view of the linkage of the variable air volume ceiling diffuser in the heating mode with the damper closed in accordance with the present invention. 
       FIG. 8   b  is a detailed plan view of the linkage of the variable air volume ceiling diffuser in the cooling mode with the damper closed in accordance with the present invention. 
       FIG. 9   a  is a detailed plan view of the linkage of the variable air volume ceiling diffuser in the heating mode with the damper open in accordance with the present invention. 
       FIG. 9   b  is a detailed plan view of the linkage of the variable air volume ceiling diffuser in the cooling mode with the damper open in accordance with the present invention. 
       FIG. 10  is a detailed plan view of the temperature set point linkage of the variable air volume ceiling diffuser in the heating mode with the damper closed in accordance with the present invention. 
       FIG. 11  is a bottom plan view of the variable air volume ceiling diffuser with a movable damper in accordance with the present invention. 
       FIG. 12  is a perspective view of the variable air volume ceiling diffuser with a movable damper having a contoured profile in accordance with the present invention. 
       FIG. 13  is end elevation view of the variable air volume ceiling diffuser and showing the contoured damper profile in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, in which like reference numerals represent like parts throughout the several views,  FIG. 1  shows a variable air volume (VAV) ceiling diffuser  10 . The diffuser  10  comprises a diffuser hood  12 , a base plate  20  hung from the hood  12  by means of base plate hangers  22  ( FIG. 3 ) and hanger slots  23  ( FIG. 2 ), a cylindrical damper stack  32  supported by the base plate  20 , a damper  42  slideably and rotatably supported on the damper stack  32 , a supply temperature actuator  46 , a first room temperature actuator  60 , a second room temperature actuator  70 , and a damper control linkage  44  ( FIGS. 3 ,  7   a , and  7   b ) for controlling the movement of the damper  42  along the height of the damper stack  32 . 
   As shown in  FIG. 4 , the base plate hanger  22  has a hanger lock  24  that, when closed, locks the base plate hanger  22  into the hanger slot  23  of the diffuser hood  12 . As shown in  FIGS. 3 and 5 , a plaque  26  is connected to the base plate  20  by means of a plaque hinge  28  at one end and a plaque latch  30  at the opposite end. The plaque latch  30  comprises two rare earth magnets. 
   As best shown in  FIG. 3 , the diffuser hood  12  includes a short air inlet  14  and a flared air outlet  16 . The air inlet  14  is connected to an air duct for receiving warm or cool air supplied by an HVAC system. The diffuser hood  12  also has a relief  13  at the flared air outlet  16  that interfaces with a ceiling system of an occupied space. 
   The damper  42 , shown in  FIGS. 3 ,  5 ,  7   a , and  7   b , is slidably mounted on the damper stack  32  by means of a damper bushing  41 . The damper stack  32  and the damper bushing  41  are circular in cross-section so that the damper  42  can rotate freely about the damper stack  32  as the damper  42  slides up and down, thereby reducing the chances of the damper  42  binding as it slides on the damper stack  32 . The damper  42  slides vertically along the damper stack  32  in response to changes in room air temperature and supply air temperature as will be more fully explained below. When the damper  42  is in the upper position and in contact with air inlet  14 , the damper  42  shuts off the flow of air through the diffuser  10  to the occupied space except for a small amount of air flowing through the damper stack  32 . As the damper  42  travels downwardly and away from contact with the air inlet  14 , the damper  42  allows proportionately more air through the diffuser  10  into the occupied space. 
   With continuing reference to  FIGS. 3 ,  7   a , and  7   b , the cylindrical damper stack  32  is mounted on the base plate  20  and protrudes upwardly into the center of the air inlet section  14 . The damper stack  32  has an upper opening  33  that receives warm or cool air from the air duct and a lower end  35  that is covered by a converging deflector  18  ( FIG. 11 ) connected to the base plate  20 . The converging deflector  18  has a restricted discharge opening  19  ( FIGS. 3 ,  7   a ,  7   b , and  11 ). The damper stack  32  further has a keyhole opening  36  adjacent the lower end  35  of the damper stack  32 . The supply temperature actuator  46 , which has a supply temperature actuator body  45  and a supply temperature actuator piston  47  ( FIGS. 7   a ,  7   b ,  8   a ,  8   b ,  9   a , and  9   b ), is mounted on the base plate  20  by means of a supply temperature bracket  48  connected to the body at  45  of supply temperature actuator  46 . The supply temperature actuator  46  extends through the keyhole opening  36 , and the body  45  of the supply temperature actuator  46  is exposed the warm or cool supply air that enters the damper stack  32  through the upper opening  33 . 
   The piston  47  of the supply temperature actuator  46  is biased to a retracted position by means of a compression supply temperature bias spring  52 . A first end  53  (left in  FIGS. 8   a ,  8   b ,  9   a , and  9   b ) of the bias spring  52  is constrained by tab  55  fixed to the body  45  of the supply temperature actuator  46 . A second end  54  (right in  FIGS. 8   a ,  8   b ,  9   a , and  9   b ) of the spring  52  engages a second end  51  of a spring keeper  49 . A first end  50  (left in  FIGS. 8   a ,  8   b ,  9   a , and  9   b ) of the spring keeper  49  is connected to the piston  47  of the supply temperature actuator  46 . The compression bias spring  52  serves to return the piston  47  of the actuator  46  to its retracted position when cool supply air is present within the damper stack  32 . When warm air is present in the damper stack  32 , the piston  47  of the supply temperature actuator  46  extends against the spring force of the bias spring  52  and compresses the bias spring  52 . 
   With reference to  FIGS. 7   a ,  7   b , and  10 , the first room temperature actuator  60  includes a first room temperature actuator body  63 . The body  63  of the first room temperature actuator  60  is affixed to the base plate  20  by means of first room temperature actuator bracket  62 . The second room temperature actuator  70  includes a second room temperature actuator body  73 . The first room temperature actuator  60  and the second room temperature actuator  70  share a common piston  61 . The body  73  of the second room temperature actuator  70  is slidably mounted on the common piston  61 . 
   With reference to  FIGS. 6   a ,  6   b ,  7   a ,  7   b , and  10 , a set point mechanism  102  is part of the damper control linkage  44  and comprises a slide activator bar  104 , a threaded heating rod  110  with a heating set point knob  112 , and a threaded cooling rod  106  with a cooling set point knob  108 . The threaded heating rod  110  is connected to one end of the slide activator bar  104 , and the threaded cooling rod  106  is connected to the other end of the slide activator bar  104 . The slide activator bar  104  is connected to the body  73  of the second room temperature actuator  70 . Room temperature bias springs  114  and  116  are connected to each end of the slide activator bar  104 . The other ends of the bias springs  114  and  116  are connected to the base plate  20  by means of anchor posts  118  and  120 . The bias springs  114  and  116  cause the common piston  61  to retract into both the first room temperature actuator body  63  and the second room temperature actuator body  73 . 
   With reference to  FIGS. 1 ,  3 ,  7   a , and  7   b , a room temperature actuator cover  38  is supported by the base plate  20  and extents over and around the first room temperature actuator  60  and the second room temperature actuator  70 . The room temperature actuator cover  38  has a room temperature air inlet  40  in communication with the occupied space. As warm or cool air enters the upper opening  33  of the damper stack  32  under pressure, the air passes across the supply temperature actuator  46  and exits through the restricted discharge opening  19  of the converging deflector  18 . As the air exits through the restricted discharge opening  19  of the converging deflector  18 , the restricted discharged opening  19  creates a jet of air moving from right to left in  FIGS. 7   a  and  7   b . The jet creates low pressure at the inlet  40  of the actuator cover  38  thereby pulling room temperature air into the air inlet  40  and across the first room temperature actuator  60  and the second room temperature actuator  70 . 
   With reference to  FIGS. 6   a ,  6   b ,  7   a , and  7   b , the damper control linkage  44  further includes a heating mode slide  74 , a cooling mode slide  80 , a slide inverter mechanism  130 , a cam actuator or roller  131 , a cam lift profile  132 , a lever mounting bracket  92 , and lever arms  90  and  91  for rotation about a lever axis  94 . A pair of lever bias springs  95  biases the levers  90  and  91  in a counterclockwise direction about the lever axis  94  ( FIGS. 7   a  and  7   b ) tending to raise the damper  42  toward its upper closed position. Consequently, the lever bias springs  95  help to offset the weight of the damper  42 . The mounting bracket  92  has bracket slots  96  ( FIG. 3 ) which allowed the lever axis  94  to be raised and lowered with respect to the base plate  20 . The lever axis  94  is raised and lowered by means of a minimum air adjustment mechanism  98  ( FIG. 5 ). The minimum air adjustment mechanism  98  comprises a bushing  99  engaging the lever axis  94  and a minimum air adjustment screw  100  that threads into the adjustment bushing  99  and is captured by the base plate  20 . By turning the minimum air adjustment screw  100 , the adjustment bushing  99  and the lever axis  94  are raised or lowered in the bracket slots  96  with respect to the base plate  20 . 
   Turning to  FIGS. 3 and 7   a , the heating mode slide  74  has a body portion  75  that extents along the length of the diffuser  10 . The body portion  75  of the heating mode slide  74  has a generally inverted U-shaped cross-section with cutouts to accommodate, for example, the damper stack  32  and the dual set point mechanism  102 . The heating mode slide  74  has a downwardly extending control tab  76  ( FIGS. 3 and 10 ) with a hole adjacent the dual set point mechanism  102  that engages the threaded heating rod  110 . The heating mode slide  74  also has a first inverter mechanism pivot  136  and a second inverter mechanism pivot  139  (left side of  FIGS. 7   a  and  7   b ) and a downwardly extending stop tab  78  midway between the ends of the heating mode slide  74 . 
   The cooling mode slide  80  has a body portion  81  that extents along the length of the diffuser  10 . The body portion  81  of the cooling mode slide  80  has a generally inverted U-shaped cross-section with cutouts to accommodate, for example, the damper stack  32  and the dual set point mechanism  102 . The cooling mode slide  80  has a downwardly extending control tab  82  ( FIGS. 7   a ,  7   b , and  10 ) with a hole adjacent the dual set point mechanism  102  (right side of  FIGS. 7   a  and  7   b ) that engages the threaded heating rod  106 . The cooling mode slide  80  also has a pair of horizontal slots  83  ( FIG. 3 , left side of  FIGS. 7   a  and  7   b ) and a downwardly extending stop tab  84  midway between the ends of the cooling mode slide  80 . 
   The heating mode slide  74  is nested within and underneath the cooling mode slide  80  so that the heating mode slide  74  and the cooling mode slide are free to slide with respect to each other and with respect to the base plate  20 . The base plate  20  has heating base plate tabs  79  and cooling base plate tabs  85  ( FIGS. 8   a ,  8   b ,  9   a , and  9   b ). The heating base plate tabs  79  engage the heating mode slide stop tab  78  to arrest the movement of the heating mode slide  74  from moving to the right in  FIGS. 6   a ,  6   b ,  7   a ,  7   b ,  8   a ,  8   b ,  9   a , and  9   b . The cooling base plate tabs  85  engage the cooling mode slide stop tab  84  to arrest the movement of the cooling mode slide  80  to the left in  FIGS. 6   a ,  6   b ,  7   a ,  7   b ,  8   a ,  8   b ,  9   a , and  9   b.    
   Turning to  FIGS. 8   a ,  8   b ,  9   a , and  9   b , the slide inverter mechanism  130  includes an inverter mechanism base  133  attached to the base plate  20  of the diffuser  10 . The cam actuator or roller  131  is attached to an inverter mechanism slide  134  that is captured by the inverter mechanism base  133  and that is free to slide horizontally on the inverter mechanism base  133 . The inverter mechanism slide  134  has a vertical slide post  135 . The vertical slide post  135  is captured by a first lever slot  138  of a first inverter mechanism lever  137  and by a second lever slot  141  of a second inverter mechanism lever  140 . The first inverter mechanism lever  137  pivots about the first inverter mechanism pivot  136 , and the second inverter mechanism lever  140  pivots about the second inverter mechanism pivot  139 . As previously disclosed, the first inverter mechanism pivot  136  and the second inverter mechanism pivot  139  are fixed to the heating mode slide  74 . The cooling mode slide slot  83  on one side  145  of the cooling mode slide  80  captures an end  143  of the first inverter mechanism lever  137 . Likewise, the cooling mode slide slot  83  on the opposite side  146  of the cooling mode slide  80  captures an end  144  of the second inverter mechanism lever  140 . 
   The heating mode operation of the diffuser  10  is illustrated with reference to  FIGS. 6   a ,  7   a , and  8   a  that show the diffuser  10  in the heating mode with the damper  42  closed, and the cooling mode operation of the diffuser  10  is illustrated with reference to  FIGS. 6   b ,  7   b , and  8   b  that show the diffuser  10  in the cooling mode with the damper  42  closed.  FIG. 9   a  shows the diffuser  10  in the heating mode with the damper  42  open, and  FIG. 9   b  shows the diffuser  10  in the cooling mode with the damper  42  open. 
   In the heating mode, warm air enters the upper damper stack opening  33  from the air inlet  14  of the diffuser  10 . The warm air passes through the damper stack  32  and exits through the restricted discharge opening  19  thereby drawing room temperature air into the room air inlet  40  of the actuator cover  38  and across the first room temperature actuator  60  and the second room temperature actuator  70 . If the duct air is warm and the room air is warm, the damper  42  is closed as shown in  FIGS. 6   a ,  7   a , and  8   a . Specifically, the warm air inside the damper stack  32  impinges on the supply temperature actuator  46  and causes the supply temperature actuator piston  47  to extend against the resistance of the supply temperature bias spring  52 . The extended supply temperature actuator piston  47  engages the cooling mode slide stop tab  84  and pins the cooling mode slide stop tab  84  against the cooling mode base plate tabs  85  on the base plate  20  thereby holding the cooling mode slide  80  in the leftward position shown in  FIGS. 6   a ,  7   a , and  8   a.    
   Because the room temperature is warm, the common piston  61  of the first room temperature actuator  60  and the second temperature actuator  70  is extended from the first room temperature actuator body  63  and from the second room temperature actuator body  73 . The extension of the common piston  61  forces the body  73  of the second room temperature actuator  70  to the right most position shown in  FIGS. 6   a  and  7   a . Because the slide activator bar  104  is attached to the body  73  of the second room temperature actuator  70 , the slide activator bar  104  is positioned in the right most position shown in  FIGS. 6   a  and  7   a . As a result, the threaded cooling rod  106  and the threaded heating rod  110  are in the right most position as well. The heating knob  112  on the threaded heating rod  110  engages the heating mode slide control tab  76  so that the heating mode slide  74  is positioned toward the right in  FIGS. 6   a  and  7   a . With the heating mode slide  74  positioned toward the right, the first inverter mechanism lever  137  and the second inverter mechanism lever  140  are rotated as shown in  FIG. 8   a . In that position, the inverter mechanism levers  137  and  140  pull the slide post  135  toward the right. As a result, the cam roller  131  engages the cam lift profiled  132  at its rightward most position as shown in  FIG. 7   a . When of the cam roller  131  is in the rightward most position, the lever arms  90  and  91  are pivoted counterclockwise about the lever axis  94  to raise the damper  42  to its upper closed position. 
   As the temperature in the occupied space decreases, the cooler room temperature air is drawn into the inlet  40  of the actuator cover  38 . The cooler room temperature air causes the common piston  61  to retract into both the first room temperature actuator  60  and the second room temperature actuator  70  as a result of the spring tension from bias springs  114  and  116 . As the common piston  61  retracts, the body  73  of the second room temperature actuator  70  moves to the left ( FIGS. 6   a ,  7   a , and  8   a ) carrying with it the slide activator bar  104 , the threaded cooling rod  106 , and the threaded heating rod  110 . As the threaded heating rod  110  moves left, the heating knob  112  also moves left allowing the heating mode slide  74  to move to the left under the influence of the force provided by the weight of the damper  42  transmitted through the lever arms  90  and  91 , the cam lift profile  132 , the cam roller  131 , and the slide inverter mechanism  130 . As the heating mode slide  74  moves left, the first inverter mechanism pivot  136  and the second inverter mechanism pivot  139  attached to the heating mode slide  74  also move to the left causing the first inverter mechanism lever  137  to rotate clockwise and the second inverter mechanism lever  140  to rotate counterclockwise. The rotation of the first inverter mechanism lever  137  and the second inverter mechanism lever  140  drives the cam roller  131  toward the left. As the cam roller  131  moves to the left, the lift profile  132  allows the lever arms  90  and  91  to rotate clockwise about the lever axis  94  thereby lowering the damper  42  to allow warm air to enter the occupied space below the diffuser  10  to raise the temperature in the occupied space. In the heating mode with the damper  42  open, the positioning of the first inverter mechanism lever  137 , the second inverter mechanism lever  140 , and the inverter mechanism slide  134  are shown in  FIG. 9   a.    
   In the cooling mode, cool air enters the upper damper stack opening  33  from the air inlet  14  of the diffuser  10 . The cool air passes through the damper stack  32  and exits through the restricted discharge opening  19  thereby drawing room temperature air into the room air inlet  40  of the actuator cover  38  and across the first room temperature actuator  60  and the second room temperature actuator  70 . If the duct air is cool and the room temperature air is cool, the damper  42  is closed as shown in  FIGS. 6   b ,  7   b , and  8   b . Specifically, the cool air inside the damper stack  32  impinges on the supply temperature actuator  46  and causes the supply temperature actuator piston  47  to retract under the influence of the bias spring  52 . As the supply temperature actuator piston  47  retracts, the right end  54  of the spring  52  and the right end  51  of the spring keeper  49  move to the right and pin the heating mode slide stop tab  78  against the heating base plate tab  79  thereby holding the heating mode slide  74  in the rightward position shown in  FIGS. 6   b ,  7   b , and  8   b.    
   Because the room temperature is cool, the common piston  61  is retracted into the first room temperature actuator  60  and the second temperature actuator  70  as a result of the room temperature bias springs  114  and  116 . The retraction of the common piston  61  causes the body  73  of the second room temperature actuator  70  to the left most position shown in  FIGS. 6   b  and  7   b . Because the slide activator bar  104  is attached to the body  73  of the second room temperature actuator  70 , the slide activator bar  104  is positioned in the left most position shown in  FIGS. 6   b  and  7   b . As a result, the threaded cooling rod  106  and the threaded heating rod  110  are in the left most position as well. The cooling knob  108  on the threaded cooling rod  106  engages the cooling mode slide control tab  82  so that the cooling mode slide  80  is position toward the left in  FIGS. 6   b  and  7   b . With the cooling mode slide  80  positioned toward the left, the first inverter mechanism lever  137  and the second inverter mechanism lever  140  are rotated as shown in  FIG. 8   b . In that position, the inverter mechanism levers  137  and  140  pull the slide post  135  toward the right. As a result, the cam roller  131  engages the cam lift profiled  132  at its rightward most position as shown in  FIG. 7   b . When of the cam roller  131  is in the rightward most position, the lever arms  90  and  91  are pivoted counterclockwise about the lever axis  94  to raise the damper  42  to its upper closed position. 
   As the temperature in the room increases, the warmer room temperature air is drawn into the inlet  40  of the actuator cover  38 . The warmer room temperature air causes the common piston  61  to extend from both the first room temperature actuator  60  and the second room temperature actuator  70  against the spring tension of bias springs  114  and  116 . As the common piston  61  extents, the of body  73  of the second room temperature actuator  70  moves to the right ( FIGS. 6   b ,  7   b , and  8   b ) carrying with it the slide activator bar  104 , the threaded cooling rod  106 , and the threaded heating rod  110 . As the threaded cooling rod  106  moves right, the cooling knob  108  also moves right allowing the cooling mode slide  80  to move to the right as a result of the force provided by the weight of the damper  42  transmitted through the lever arms  90  and  91 , the cam lift profile  132 , the cam roller  131 , and the slide inverter mechanism  130 . As the cooling mode slide  80  moves right, cooling mode slide slots  83  attached to the cooling mode slide  80  also move to the right causing the first inverter mechanism lever  137  to rotate clockwise and the second inverter mechanism lever  140  to rotate counterclockwise. The rotation of the first inverter mechanism lever  137  and the second inverter mechanism lever  140  drives the cam roller  131  toward the left. As the cam roller  131  moves to the left, the lift profile  132  allows the lever arms  90  and  91  to rotate clockwise thereby lowering the damper  42  to allow cool air to enter the occupied space below the diffuser  10 . In the cooling mode with the damper  42  open, the positioning of the first inverter mechanism lever  137 , the second inverter mechanism lever  140 , and the inverter mechanism slide  134  are shown in  FIG. 9   b.    
   The engineered cam lift profile  132  allows the small differential horizontal motion of the heating mode slide  74  and the cooling mode slide  80  described above to be amplified and predictably converted into a vertical motion of the damper  42 . 
   With reference to  FIG. 10 , the temperature in the occupied space is set in the heating mode by adjusting the heating knob  112  along the threaded heating rod  110 . Similarly, the temperature in the occupied space is set in the cooling mode by adjusting the cooling knob  108  along the threaded cooling rod  106 . Particularly, in the heating mode, moving the heating knob  112  toward the left in  FIGS. 6   a ,  7   a ,  8   a , and  10  increases the temperature in the occupied space. Similarly, in the cooling mode, moving the cooling knob  108  toward the right in  FIGS. 6   b ,  7   b ,  8   b , and  10  increases the temperature in the occupied space. Set point indices  113  ( FIG. 11 ) may be provided adjacent the set point knobs  108  and  112  to aid in the adjustment of the set point knobs  108  and  112 . The set point knobs  108  and  112  are accessible from the occupied space below the diffuser by simply opening the plaque  26 . 
   In connection with the installation of the diffuser  10  as part of a complete HVAC system, the damper  42  is set to its fully open position in order to balance the HVAC system to which the diffuser  10  is connected. In order to set the damper  42  is set to its fully open position, the adjustment screw  100  ( FIG. 5 ) is rotated in order to raise the lever axis  94  in the bracket slots  96  ( FIG. 3 ). Visible indices  115  ( FIG. 11 ) are provided around the head of the adjustment screw  100  in order to facilitate adjustment to the fully open position. The adjustment screw  100  in conjunction with the adjustment bushing  99  also controls the minimum air opening for the damper  42 . Again, by adjusting the lever axis  94  up or down, the minimum airflow is set for the damper  42 . Further, the indices  115  around the head of the adjustment screw  100  provide assistance in facilitating the adjustment of the minimum airflow for the damper  42 . The airflow adjustment screw  100  is accessible from the occupied space below the diffuser by simply opening the plaque  26 . 
     FIGS. 12 and 13  show an alternative embodiment of the ceiling diffuser  210  in accordance with the present invention. Particularly, the alternative embodiment has a profiled damper  242  having an upper section  154 , a transition section  156 , and a lower section  152 . The profiled damper  242  has a damper bushing  241  that is slidably mounted on a modified damper stack  232 . The modified damper stack  232  has splines  150  spaced about the outside circumference of the damper stack  232  and extending vertically along the outside of the damper stack  232 . The splines engage matching recesses  158  on the damper bushing  241  so that the bushing  241  cannot be angularly displaced about the damper stack  232  as the damper  242  is raised and lowered. The profiled damper  242  minimizes noise when the damper  242  is in its fully opened position as shown in  FIGS. 12 and 13 . 
   While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.