Abstract:
An air-conveying device for use in an HVAC system having an interior surface and an exterior surface. An air-moving device is arranged and disposed to move air through the air-conveying device adjacent to the interior surface of the air-conveying device. The air-conveying device conveys air having passed through an HVAC heat exchanger. The air-conveying device includes one or more openings disposed and arranged to provide a pressure differential sufficient to cause passage of air through the openings from an area adjacent to the interior surface to an area adjacent to the exterior surface in order to decrease aerodynamic drag.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is related to devices for conveying air. In particular, the present invention is directed to a diffuser and/or orifice for use in HVAC heat exchanger units.  
       BACKGROUND OF THE INVENTION  
       [0002]     HVAC systems will typically include a heat exchanger unit having a fan arranged to pass air over a heat exchanger. As air is discharged from the unit, the air typically passes through a diffuser/orifice. The diffuser/orifice is a device that permits the passage of air out of a heat exchanger. Diffuser/orifices are typically fabricated with a geometry, which results in less backpressure and an increased airflow. One drawback of the diffuser/orifice is that the flow at or near the diffuser/orifice surface experiences undesirable flow characteristics. In particular, the fluid near the surface of the diffuser/orifice experiences boundary layer formation. Boundary layer separation may also occur further increasing the thickness of the boundary layer region.  
         [0003]     Air passing over flat surfaces may flow in a laminar flow profile. Laminar flow profiles experience low drag and results in larger, desirable flow rates. A boundary layer forms as a result of friction between the air and the surface. The boundary layer thickness is defined as the locus of points where the velocity parallel to the flow surface reaches 99% of the mean stream velocity. Therefore, the thicker a boundary layer is, the less area there is available for flow at maximum velocity when passing through the orifice. Separation of the boundary layer from the surface, called boundary layer separation, causes recirculation and/or turbulent flow. Boundary layer separation is a particular problem in applications where the flow of a fluid diverges. In diffusers, boundary layer separation may occur as air passes out of the unit and experiences an air pressure differential. Diverging flow typically occurs when the flow of air out of the heat exchanger unit is diffused through a diffuser/orifice having a flared outlet. The diverging flow provides a reduction in air pressure, which also reduces backpressure against the fan, but may increase the amount of undesirable turbulent flow and susceptibility to boundary layer separation. Air traveling out of a heat exchanger unit through a diffuser/orifice may experience an adverse pressure gradient along the surface of the orifice. The result is that the boundary layer breaks away or separates from the orifice surface forming a broad pulsating wake.  
         [0004]     Another type of known diffuser/orifice device is a cylindrical orifice, which conveys air from spaces within heat exchanger units to outside of the heat exchanger units. In diffuser/orifice devices having a substantially cylindrical geometry, the air passing through the cylinder has a relatively large boundary layer. The large boundary layer is due to the friction between the air and the surface of the cylinder. The shape of the entrance to the cylinder plays a large role in determining the eventual thickness of the boundary layer. A smooth and curved orifice entrance will result in less resistance to fluid flow through the orifice. Sharp edges at the orifice entrance result in increased resistance to flow. This resistance is due to the formation of a large boundary layer region that forms just past the orifice entrance. The large boundary layer is susceptible to boundary layer separation and/or turbulent flow, particularly at larger flow rates. In addition, the cylindrical geometry results in a backpressure against the fan that decreases the quantity of air flowing through the diffuser orifice.  
         [0005]     As the boundary layer is drawn away from the surface of the diffuser/orifice, the flow loses at least a part of the laminar flow profile and becomes more turbulent. Turbulent flow has increased drag at the surface, has a lower airflow rate and increases backpressure against the fan. The turbulent flow characteristics of the boundary layer are undesirable for heat exchanger unit applications because a significant amount of energy present in the fluid is lost to aerodynamic drag and recirculation of the turbulent flow. The fan blades may extend at least a portion of the way into the orifice. This extension places the tips of the fan blades within this turbulent region rendering this portion of the blade less efficient and may result in increased fan noise. As a result, the fan requires a greater amount of energy to move the air through the diffuser/orifice.  
         [0006]     What is needed is a system and method for decreasing the amount of boundary layer separation and/or turbulent flow occurring in orifice/diffusers in order to more efficiently move air out of a heat exchanger unit.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention includes an air-conveying device for use in an HVAC system having an interior surface and an exterior surface. An air-moving device is arranged and disposed to move air through the air-conveying device adjacent to the interior surface of the air-conveying device. The air-conveying device conveys air having passed through an HVAC heat exchanger. The air-conveying device includes one or more openings disposed and arranged to provide a pressure differential sufficient to cause passage of air through the openings from an area adjacent to the interior surface to an area adjacent to the exterior surface in order to decrease aerodynamic drag.  
         [0008]     Another embodiment of the invention includes a method for reducing aerodynamic drag in an air-conveying device. The method includes providing an air-conveying device having an interior and exterior surface. A flow of air is provided with an air-moving device from a heat exchanger through the air-conveying device and along the interior surface. Flow of a portion of air through the air-conveying device is permitted from an area of higher pressure air adjacent to the interior surface to an area of lower pressure air adjacent to the exterior surface through openings in the air-conveying device to reduce aerodynamic drag.  
         [0009]     An advantage of the present invention is that the air flowing through the diffuser/orifice experiences reduced boundary layer separation because the boundary layer is drawn closer to the surface of the diffuser/orifice. The reduction in boundary layer permits the air to flow through the diffuser/orifice in a substantially laminar flow profile, reducing the backpressure against the fan and decreasing the power required by the fan to exhaust the air out of the heat exchanger unit.  
         [0010]     Another advantage of the present invention is that the fan capacity in a heat exchanger unit may be decreased without decreasing the total amount of airflow through the system.  
         [0011]     Another advantage of the present invention is that cylindrical diffuser/orifices may be used with substantially the same fan power requirements as diffuser/orifices having a flared geometry, and without the expensive manufacturing costs associated with flared diverging outlet diffuser/orifices.  
         [0012]     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  schematically illustrates a cutaway view of a known diffuser/orifice system.  
         [0014]      FIG. 2  schematically illustrates a cutaway view of an embodiment of the present invention.  
         [0015]      FIG. 3  schematically illustrates a cutaway view showing airflow through a diffuser/orifice of the present invention.  
         [0016]      FIG. 4  schematically illustrates a profile of airflow over a surface of a diffuser/orifice of the present invention.  
         [0017]      FIG. 5  schematically illustrates a perspective view of an embodiment of the present invention.  
         [0018]      FIG. 6  schematically illustrates a perspective view of an alternate embodiment of the present invention.  
         [0019]      FIG. 7  schematically illustrates a cutaway view of a known diffuser/orifice system.  
         [0020]      FIG. 8  schematically illustrates a cutaway view of an alternate embodiment of the present invention.  
         [0021]      FIG. 9  schematically illustrates a cutaway view showing airflow through an alternate embodiment of a diffuser/orifice of the present invention.  
         [0022]      FIG. 10  schematically illustrates a profile of airflow over a surface of an alternate embodiment of a diffuser/orifice of the present invention.  
         [0023]      FIG. 11  schematically illustrates a perspective view of an alternate embodiment of the present invention.  
         [0024]      FIG. 12  schematically illustrates a perspective view of an alternate embodiment of the present invention  
         [0025]      FIG. 13  schematically illustrates a cutaway view of a diffuser/orifice in an outdoor unit according to the present invention.  
         [0026]      FIG. 14  schematically illustrates a cutaway view of a diffuser/orifice in an outdoor unit according to an alternate embodiment of the present invention. 
     
    
       [0027]     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 1  shows a known diffuser/orifice for use in a heat exchanger unit. Inlet air  106  is drawn by a fan  104  through a diffusion apparatus  102 . The diffusion apparatus  102  has an inlet end  101 , having a first diameter and an outlet end  103  having a second diameter. In the arrangement shown in  FIG. 1 , the first diameter is typically smaller than the second diameter. The inlet air  106  passes into the diffusion apparatus  102  at the inlet end  101  and exhausts from the unit, preferably to the atmosphere, from the outlet end  103 . The larger diameter of the outlet end  103  provides a reduction in air pressure for the outlet air  108 . In addition, diffusion apparatus  102  includes an interior surface  112  receiving airflow from fan  104  and an exterior surface  110  open to atmosphere pressure. As air flows along the interior surface  112  of the diffusion apparatus  102 , a boundary layer  114  is formed. The lower pressure outlet air  108  draws the air in the boundary layer  114  away from the surface, causing boundary layer separation. The result of the boundary layer separation is circulating airflow  120 , which has increased drag and reduces the flow rate of outlet air  108 . The circulating airflow  120  circulates on itself and may reverse direction at or near the surface of the diffusion apparatus  102 . Further, even without boundary layer separation, the presence of a boundary layer results in a resistance to flow and this resistance increases as the boundary layer thickness increases. The presence of the boundary layer has the effect of reducing the area available for fluid flow.  
         [0029]      FIG. 2  shows a diffuser/orifice according to an embodiment of the present invention. The diffuser/orifice shown in  FIG. 2  includes a diffusion apparatus  202  and fan  104 . A diffusion apparatus  202  according to this embodiment of the invention is configured with a geometry that diffuses air passing through the diffusion apparatus  202 . As shown in  FIG. 2 , the diffusion apparatus  202  has a circular cross-section that increases in diameter from the inlet end  101  to the outlet end  103 . Although the invention has been described and shown with respect to a circular cross-section, any geometry that is capable of exhausting air out of a heat exchanger unit may be used. The geometry of the diffusion apparatus  202  shown in  FIG. 2  includes a geometry that causes a reduction in air pressure as the air is exhausted. This reduction of air pressure reduces the backpressure against fan  104  present in heat exchanger unit applications. The reduction in backpressure reduces the power requirements for fan  104 . The inlet air  106  flows into the fan  104  to the inlet end  101  of the diffusion apparatus  202 . As the fan  104  moves the air, the air pressure is increased at the inlet end  101  to provide the movement of the air through the diffusion apparatus  202 . Outlet air  108  travels from the inlet end  101  through the diffusion apparatus  202 . The path of the air includes airflow that follows the contour of interior surface  112 . The flow of air along interior surface  112  is in frictional contact with the interior surface  112  and forms a boundary layer  214 . The characteristics of the airflow of the boundary layer  214  are preferably at least partially laminar flow. Laminar flow profiles allow the outlet air  108  to exit the diffusion apparatus  202  with a greater reduction in air pressure from inlet end  101  to outlet end  103  and a greater reduction in backpressure against the fan  104  than turbulent flow profiles. The diffusion apparatus  202  according to the invention further includes openings  205  arranged and disposed in the diffusion apparatus  202  to allow passage of air from an interior high-pressure area  310  to an exterior low-pressure area  315 . The interior high-pressure area  310  is an area within the diffusion apparatus  202  that has increased air pressure due to movement of the air by the fan  104 . The low-pressure area  315  is an area present outside of the diffusion apparatus  202  having a lower pressure than pressure within the diffusion apparatus  202 . The low pressure area  315  may be an area either open to outdoor atmospheric pressure or includes an area from which inlet air  106  is drawn. The air traveling over interior surface  112  in boundary layer  214  is drawn into openings  205  due to a pressure differential present between high pressure area  310  and the low pressure area  315 . The air drawn from the high pressure area  310  to the low pressure area  315  reduces the thickness of the boundary layer  214 , reduces the susceptibility to boundary layer separation and maintains substantially laminar flow as the outlet air  108  leaves the diffusion apparatus  202 .  
         [0030]      FIG. 3  schematically shows air moving in flow directions  305  through the diffusion apparatus  202 . The diffuser/orifice shown in  FIG. 3  is configured as shown and described above with respect to  FIG. 2 . The air near the center of the diffusion apparatus  202  travels in a substantially parallel flow directions  305 . The air near the interior surface  112  flows in a flow direction  305  that follows the contour of the interior surface  112 . The low-pressure area  315  near the exterior surface  110  of the diffusion apparatus  202  draws the air from the high-pressure area  310  to the interior of the diffusion apparatus  202  to the exterior of the diffusion apparatus  202 . The air drawn through openings  205  provide an additional decrease in air pressure as the air travels through the diffusion apparatus  202  and out of the heat exchanger unit. The additional decrease in air pressure decreases the amount of backpressure against the fan, reducing the power requirements for the fan. The amount of power savings by the fan over a diffuser/orifice without openings  205  include power savings up to about 30%, preferably up to about 40%. Backpressure against the fan is due to aerodynamic drag experienced by the air passing through the diffusion apparatus  202 . The aerodynamic drag is a force in a direction opposite the flow of air through the diffusion apparatus  202 . Aerodynamic drag is a result of friction between the air and the surface of the diffusion apparatus  202  and the loss of fluid momentum due to turbulent flow. The force resulting from the aerodynamic drag increases the amount of power required to convey air through the diffusion apparatus  202 , increasing the amount of power required by the fan.  
         [0031]      FIG. 4  shows an enlarged view of a portion of the diffusion apparatus  202 , as shown and described with respect to  FIGS. 2-3 , according to the present invention illustrating the reduction in the thickness of the boundary layer  214 .  FIG. 4  includes interior surface  112  and exterior surface  110 . As shown, boundary layer  214  is formed on the surface as outlet air  108  flows over interior surface  112 . As the boundary layer air  410  travels over openings  205 , a portion of the boundary layer air  410  is drawn from the higher pressure area  310  near the interior surface  112  to the lower pressure area  315  near the exterior surface  110 . As the boundary layer air  410  is drawn through the surface, the thickness of the boundary layer  214  is reduced, thereby reducing the thickness of boundary layer  214 , decreasing the susceptibility to boundary layer separation and increasing the laminar flow characteristics of the boundary layer  214 .  
         [0032]      FIG. 5  schematically shows a perspective view of a diffuser/orifice according to the present invention.  FIG. 5  shows a diffusion apparatus  202 , a fan  104 , an inlet air  106  and outlet air  108 . Openings  205  are shown with a circular geometry, wherein air is permitted to flow from the high pressure area  310  to low pressure area  315 . Openings  205  may be fabricated in the diffusion apparatus  202  using any suitable manufacturing technique, including, but not limited to, cutting, drilling and/or punching. As described above with respect to  FIGS. 2-4 , the air is moved by fan  104  through diffusion apparatus  202 . As the air travels through diffusion apparatus  202 , a portion of outlet air  108  is drawn through openings  205 . As the air is drawn through openings  205 , the thickness of boundary layer  214  (not shown in  FIG. 5 ) is reduced.  
         [0033]      FIG. 6  schematically shows a perspective view of a diffuser/orifice according to another embodiment of the present invention.  FIG. 6  shows a diffusion apparatus  202 , a fan  104 , an inlet airflow  106  and outlet airflow  108 . Openings  205  are shown with a slot geometry, wherein air is permitted to flow from the high pressure area  310  to low pressure area  315 . The slot configuration provides an elongated opening that provides a greater surface area in the direction of flow for which the air may be drawn. As in  FIG. 4 , openings  205  may be fabricated in the diffusion apparatus  202  using any suitable manufacturing technique, including, but not limited to, cutting, drilling and/or punching. The airflow through diffusion apparatus  202  is substantially the same as shown and described above with respect to  FIG. 5 .  
         [0034]     Although  FIGS. 5 and 6  show embodiments of the present invention that include circular and slot geometries, any geometry of opening may be used so long as the opening permits the drawing of air from the interior high pressure area  310  to the exterior low pressure area  315 . Additionally, the openings  205  may be positioned along the surface of the diffusion apparatus at any location that provides a reduction in boundary layer thickness.  
         [0035]      FIG. 7  shows a known diffuser/orifice having a cylindrical geometry. As shown and described in  FIG. 1 , the inlet air  106  is moved by fan  104 , which increases the pressure of the air entering the diffusion apparatus  702 . As the air contacts the interior surface  112  of the diffusion apparatus  702  at inlet end  101 , the air forms a circulating airflow  120  having a turbulent flow profile, which reduces the pressure drop as the air travels through the diffusion apparatus  702 . In addition, the circulating airflow  120  increases the backpressure against the fan  104 . The increased backpressure and reduced pressure drop results in a greater power requirement from fan  104 . The cylindrical geometry provides a limited pathway for the air to pass, preventing the pressure from reducing until the air exits the diffusion apparatus at outlet end  103 . The exhausting of high-pressure air at outlet end  103  further increases the circulating airflow  120  as the outlet air  108  exits the diffusion apparatus  702 .  
         [0036]      FIG. 8  shows a diffusion/orifice according to an alternate embodiment of the present invention. The arrangement and operation of  FIG. 8  is substantially the same as the arrangement shown and described with respect to  FIG. 2 . However, unlike  FIG. 2 , the diffusion apparatus  802  shown in  FIG. 8  has a substantially cylindrical geometry, including openings  205 . A diffusion apparatus  802  according to this embodiment of the invention is configured with a geometry that passes air through the diffusion apparatus  802  where a portion of the air is drawn through openings  205 . In this embodiment, the diameter of inlet end  101  and outlet end  103  is substantially the same. Although the invention has been described and shown with respect to a circular cross-section, any geometry that is capable of exhausting air out of a heat exchanger unit may be used. The geometry of the diffusion apparatus  802  shown in  FIG. 8  includes a geometry that conveys air, including, but not limited to, square, rectangular or oval cross-sections. The reduction of air pressure resulting from the air passing through openings  205  reduces the amount of aerodynamic drag through the diffusion apparatus  802 . The reduction in aerodynamic drag reduces the power requirements for fan  104 .  
         [0037]      FIG. 9  schematically shows air-moving in flow directions  305  through the diffusion apparatus  802 . The diffuser/orifice is configured as shown and described above, with respect to  FIG. 8 . The air near the center of the diffusion apparatus  802  travels in a substantially parallel flow directions  305 . The air near the interior surface  112  flows in a flow direction  305  that follows the contour of the interior surface  112 . The low-pressure area  315  near the exterior surface  110  of the diffusion apparatus  802  draws the air from the high-pressure area  310  at the interior of the diffusion apparatus  802  to the exterior of the diffusion apparatus  802 . The air drawn through openings  205  provide an additional decrease in air pressure as the air travels through the diffusion apparatus  802  and out of the heat exchanger unit. The additional decrease in air pressure decreases the amount of aerodynamic drag through the diffusion apparatus  802 , reducing the power requirements for the fan  104 .  
         [0038]      FIG. 10  shows an enlarged view of a portion of the surface of the diffusion apparatus  802 , as shown and described with respect to  FIGS. 8-9 , according to the present invention, illustrating the reduction in the thickness of the boundary layer  214 .  FIG. 10  includes interior surface  112  and exterior surface  110 . As shown, boundary layer  214  is formed on the surface as outlet air  108  flows over interior surface  112 . As the boundary layer air  410  travels over openings  205 , a portion of the boundary layer air  410  is drawn from the higher pressure area  310  near the interior surface  112  to the lower pressure area  315  near the exterior surface  110 . As the boundary layer air  410  is drawn through the surface, the thickness of the boundary layer  214  is reduced, decreasing the susceptibility to boundary layer separation, increasing the effective flow area, and increasing the laminar flow characteristics of the boundary layer  214 .  
         [0039]      FIG. 11  schematically shows a perspective view of a diffuser/orifice according to an alternate embodiment of the present invention.  FIG. 11  shows a diffusion apparatus  802 , a fan  104 , an inlet air  106  and outlet air  108  arranged as shown and described above with respect to  FIG. 5 . However, unlike  FIG. 5 , the geometry of diffusion apparatus  802  is substantially cylindrical. As in  FIG. 5 , the openings  205  are shown with a circular geometry, wherein air is permitted to flow from the high pressure area  310  to low pressure area  315 .  
         [0040]      FIG. 12  schematically shows a perspective view of a diffuser/orifice according to another embodiment of the present invention.  FIG. 12  shows diffusion apparatus  802  arranged substantially the same as  FIG. 11 . However, openings  205  in  FIG. 12  are shown with a slot geometry, wherein air is permitted to flow from the high pressure area  310  to low pressure area  315 . The slot configuration provides an elongated opening that provides a greater surface area in the direction of flow for which the air may be drawn.  
         [0041]     Although  FIGS. 11 and 12  show embodiments of the present invention that include circular and slot geometries, any geometry of opening may be used so long as the opening permits the drawing of air from the interior high pressure area  310  to the exterior low pressure area  315 .  
         [0042]      FIG. 13  schematically illustrates a heat exchanger unit  1300  according to an embodiment of the present invention. The heat exchanger unit  1300  includes a diffuser/orifice arranged as shown and described with respect to  FIG. 2 . Heat exchanger unit  1300  also includes a housing  1310  onto which the diffuser/orifice is attached. The diffuser/orifice includes a flared geometry. Heat exchanger coils  1320  are also attached to the housing  1310 . The heat exchanger coils  1320  may be any heat exchanger coils known in the art that provide heat exchange between refrigerant and air. Outdoor air  1330  is drawn by fan  104  through the heat exchanger coils  1320 . The inlet air  106  is then directed through the diffuser/orifice and exhausted to the atmosphere as outlet air  108 .  
         [0043]      FIG. 14  schematically illustrates a heat exchanger unit  1300  according to an embodiment of the present invention. The heat exchanger unit  1300  includes a diffuser/orifice arranged as shown and described with respect to  FIG. 8 . Like in  FIG. 13 , heat exchanger unit  1300  also includes a housing  1310  onto which the diffuser/orifice is attached. However, in the embodiment shown in  FIG. 14 , the geometry of the diffuser/orifice is substantially cylindrical. In addition, heat exchanger coils  1320  are attached to the housing  1310 . Outdoor air  1330  is drawn by fan  104  through the heat exchanger coils  1320 . The inlet air  106  is then directed through the diffuser/orifice and exhausted to the atmosphere as outlet air  108 .  
         [0044]     While the invention has been described with respect to a diffuser/orifice, any surface that experiences boundary layer separation in an HVAC system may use the system and method of the present invention, such as centrifugal blower housings. In particular, on the exiting side of the centrifugal blower housing, the decrease in boundary layer thickness may provide an increase in the effective flow area.  
         [0045]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.