Abstract:
An apparatus and method for attenuating the sound generated by a fan powered terminal unit or other equipment in an HVAC (heating, ventilating, and air conditioning) system is described. The apparatus utilizes internal geometry to minimize noise due to air disturbances and aerodynamic effects within the apparatus. Specifically, a silencer is described comprising a casing having an inlet and an outlet; a condensate deflector positioned at the inlet to the casing; at least one baffle being operable to attenuate noise in a gas flowing through the silencer; and an air pathway through the silencer, defined by positions of the condensate deflector and the at least one baffle within the casing. The air pathway is angled or curved to substantially minimize the line-of-sight pathway from the inlet to the outlet.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part application based on U.S. application Ser. No. 12/047,816, filed Mar. 13, 2008, which claims priority to U.S. provisional application No. 60/895,152, filed Mar. 16, 2007, both of which are incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to a silencing unit for HVAC (heating, ventilating, and air conditioning) systems, and more particularly, to a silencer with an integral condensation plate. 
       BACKGROUND OF THE INVENTION 
       [0003]    Commercial HVAC systems may have a contained “Fan Coil” (“FC”) for the purpose of providing an outlet for commercial ventilation systems into the rooms of a building or other structure equipped with an HVAC system. An FC typically consists of the following components: 1) centrifugal fan, 2) motor, 3) insulated casing, 4) air inlet (with or without damper), and 5) Heating/Cooling Coils. 
         [0004]    In commercial HVAC installations, a “silencer” (or “attenuator”) is often attached to the inlet or outlet of an FC in order to attenuate the sound produced by the high-velocity air entering the FC. Such silencers have typically comprised an air duct (typically from three to five feet in length) that is lined internally with insulation to attenuate the noise produced by the air flowing through the FC. Such internal insulation is also known as a “baffle” and is usually held in place by perforated sheet metal. The perforations in the metal allow the air traveling through the silencer to interact with the insulation material contained inside the baffle. The silencer is attached to the inlet or the outlet of the FC and acts to attenuate the noise that is produced by the FC. This attenuation is achieved due to the conversion of acoustic energy into heat energy as the air molecules inside the silencer create friction when they collide with the lined insulation. 
         [0005]    The noise generated by an FC or other HVAC component can be separated into two components: 1) noise due to the air disturbance created in the immediate vicinity of the rotating fan blades and 2) aerodynamic noise due to the fan-induced air flow that has variable pressure regions within the fan discharge velocity profile and the air flow interaction with geometry changes in the air stream. The insulation contained in silencers is typically designed to minimize both sources of noise. 
         [0006]    There is a need for an improved silencer, particularly one which is compact, efficient and durable. 
         [0007]    Fan Coil units are capable of producing condensate carryover when applied in higher humidity conditions. This design helps prevent carryover as an integral part of the unit. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the invention to provide an improved silencer. 
         [0009]    The exemplary system described herein (a fan coil quiet unit “FCQ”) includes an apparatus and method for attenuating the sound generated by a fan coil unit or other HVAC equipment. 
         [0010]    Embodiments of the invention can minimize the noise generated by the variable pressure regions within the FCQ unit by closely coupling the noise-attenuating, insulation-lined silencing portion of the unit to the housing of the centrifugal fan inside the unit. Such close-coupling minimizes the turbulence created by the centrifugal fan and thus minimizes the associated noise. 
         [0011]    Embodiments of the invention also minimize noise within the FCQ by creating a constant, uniform cross-sectional profile of the air traveling through the unit. This uniform cross-sectional profile minimizes the turbulence created when air exiting a typical FC enters a silencer with a larger (or smaller) cross-sectional area. The decreased turbulence in the airflow of the invention, in turn, helps minimize the noise generated by the FCQ. 
         [0012]    Embodiments of the invention minimize high-frequency noise due to the internal angled or curved geometry of the FCQ. Such geometry obstructs any direct line-of-sight pathway out of the unit that would otherwise allow high-frequency noise to escape without much attenuation. Traditional silencers lack any such internal geometry and instead allow high-frequency noise to exit the silencer without contacting the baffles of the silencer. Therefore, the high-frequency noise in a traditional silencer can escape without much attenuation. 
         [0013]    This silencer is described as comprising a casing having an inlet and an outlet; a condensate deflector positioned at the inlet to the casing; at least one baffle being operable to attenuate noise in a gas flowing through the silencer; and an air pathway through the silencer, defined by positions of the condensate deflector and the at least one baffle within the casing. The air pathway is angled or curved to substantially minimize the line-of-sight pathway from the inlet to the outlet. The condensate deflector may also have a leading edge at the inlet to the casing and a trailing edge fixed to a leading edge of the baffle, the trailing edge of the baffle being fixed to the outlet of the casing. 
         [0014]    Further objects, features, and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a side elevation view of a centrifugal fan and the velocity and pressure profile of the air leaving the centrifugal fan in a prior art FC. 
           [0016]      FIG. 2A  is a top cut away view of a prior art FC coupled to a prior art silencer with vertical baffles. 
           [0017]      FIG. 2B  is a side cross-sectional view of a prior art FC coupled to a prior art silencer with horizontal baffles. 
           [0018]      FIG. 3A  is a top cut away view of a prior art FC coupled to a prior art silencer. 
           [0019]      FIG. 3B  is a side cross-sectional view of  FIG. 3A . 
           [0020]      FIG. 3C  is an end view along line  3 C of  FIG. 3B . 
           [0021]      FIG. 3D  is a cross-sectional view along line  3 D of  FIG. 3B . 
           [0022]      FIG. 4A  is a top cut away view of an embodiment of an FCQ in accordance with the invention. 
           [0023]      FIG. 4B  is a side cross-sectional view of  FIG. 4A . 
           [0024]      FIG. 4C  is an end view along line  4 C of  FIG. 4B . 
           [0025]      FIG. 4D  is a cross-sectional view along line  4 D of  FIG. 4B . 
           [0026]      FIG. 4E  is a magnified cross-sectional view of inset  4 E of  FIG. 4B . 
           [0027]      FIG. 5A  is a top cut away view of an embodiment of an FCQ in accordance with the invention. 
           [0028]      FIG. 5B  is a side cross-sectional view of  FIG. 5A . 
           [0029]      FIG. 5C  is an end view along line  5 C of  FIG. 5B . 
           [0030]      FIG. 5D  is a cross-sectional view along line  5 D of  FIG. 5B . 
           [0031]      FIG. 5E  is a magnified cross-sectional view of inset  5 E of  FIG. 5B . 
           [0032]      FIG. 6A  is a top cut away view of an embodiment of an FCQ in accordance with the invention. 
           [0033]      FIG. 6B  is a side cross-sectional view of  FIG. 6A . 
           [0034]      FIG. 6C  is an end view along line  6 C of  FIG. 6B . 
           [0035]      FIG. 6D  is a cross-sectional view along line  6 D of  FIG. 6B . 
           [0036]      FIG. 6E  is a magnified cross-sectional view of inset  6 E of  FIG. 6B . 
           [0037]      FIG. 7A  is a top cut away view of an embodiment of an FCQ in accordance with the invention. 
           [0038]      FIG. 7B  is a side cross-sectional view of  FIG. 7A . 
           [0039]      FIG. 7C  is an end view along line  7 C of  FIG. 7B . 
           [0040]      FIG. 7D  is a cross-sectional view along line  7 D of  FIG. 7B . 
           [0041]      FIG. 7E  is a magnified cross-sectional view of inset  7 E of  FIG. 7B . 
           [0042]      FIG. 8  presents a side cross-sectional view of a silencer with an integrated condensate diverter in accordance with the invention. 
           [0043]      FIG. 9  presents a side cross-sectional view of the silencer of  FIG. 8 , including dimensions. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]      FIG. 1  is an illustration of the velocity and pressure profile of a centrifugal fan  101  in a typical prior art FC  100 . The centrifugal fan  101  is enclosed in a housing  103  and blows air out into a discharge duct  102  or attached silencer. The housing  103  of the fan  101  has a cutoff plate  104  on the lower edge of the housing  103 . The cutoff plate  104  creates a low pressure area  105  immediately behind the cutoff plate  104 . The high-velocity air exiting the fan  101  exhibits a non-uniform bulge  106  of high pressure. As the air travels down the discharge duct  102 , the bulge of high pressure will gradually even out as illustrated in  107 ,  108 ,  109 , and  110 . The turbulence generated as the high pressure bulge gradually evens out will create noise in the FC  100 . 
         [0045]      FIGS. 2A and 2B  are illustrations of the close-coupling of a prior art FC  201  with a prior art silencer  202 . Such silencers typically have vertical baffles  203   a  or horizontal baffles  203   b  (with respect to the FC  201 ) in order to attenuate the sound produced by the FC  201 . Prior art silencers  202  typically have a wider cross-sectional area than a corresponding FC  201 , creating a wide area  204  inside the silencer  202 . This wide area  204  creates a space where turbulence can develop in the silencer  202 , thus unnecessarily increasing the noise level in the silencer  202 . In addition, prior art FCs  201  contain the cutoff plate  205  described previously, which also increases the noise generated by the FC  201  due to the non-uniform bulge of high pressure exiting the FC  201 . The cross-sectional area of the blower outlet  210  of prior art FCs  201  is typically larger than the cross-sectional area of the air pathway  206  of prior art silencers  202 . Therefore a “nose”  209  is created where the air exiting the blower outlet  210  collides into the baffles  203   a ,  203   b  inside the silencer  202 . This causes added turbulence and increased noise. 
         [0046]    Prior art FCs  201  and silencers  202  also have a direct line-of-sight pathway  206  from the centrifugal fan  207  of the FC  201  to the discharge outlet  208  of the silencer  202 . As a consequence of such a direct line-of-sight pathway  206 , high-frequency sounds can travel relatively unobstructed through the silencer  202 . This is because the shorter wavelengths of high-frequency sound waves produce less displacement of the air molecules and hence those air molecules are less likely to collide with the baffles  203   a ,  203   b  inside the silencer  202 . This “beaming” effect of high-frequency sounds thus reduces the effectiveness of prior art silencers  202  in reducing high-frequency noise. 
         [0047]      FIGS. 3A-3D  are depictions of a prior art FC  301  closely-coupled to a prior art silencer  304  with only a half-baffle design. That is, the silencer  304  contains a baffle  306  on only a single internal wall. This half-baffle silencer  304  still contains a nose  302  which leads to increased turbulence and noise. The nose  302  is caused because the cross-sectional air pathway  305  of the silencer  304  is narrower than the cross-sectional area of the blower outlet  303  of the FC  301 . 
         [0048]      FIG. 3C  depicts an end view of the silencer  304  and the perforated metal casing  353  that encloses the insulating material  354  of the baffle  306 .  FIG. 3C  also shows the casing  351  of the silencer  304  and the casing  352  of the FC  301 . 
         [0049]      FIG. 3D  depicts a cross-sectional view of the insulating material  354  that comprises the baffle  306  of the silencer  304 .  FIG. 3D  also shows the casing  351  of the silencer  304  and the casing  352  of the FC  301 . 
         [0050]      FIGS. 4A-4E  depict an embodiment of an FCQ  401  in accordance with the invention. FCQ  401  contains a silencer inlet extension  402  which connects the top edge  403  of the baffle  409  contained in the silencing portion  404  of the FCQ  401  directly to the cutoff plate  405  of the centrifugal fan  406  housed in the FCQ  401 . The silencer inlet extension  402  eliminates the low-pressure area  105  caused by the cutoff plate  104  in prior art FCs ( FIG. 1 ). Therefore, the air exiting the centrifugal fan  406  does not contain a non-uniform bulge of high pressure as it travels down the air pathway  407  of the silencing portion  404  of the FCQ  401 . 
         [0051]    In addition, the cross-sectional area of the blower outlet  408  substantially equals the cross-sectional area of the air pathway  407  of the silencing portion  404  of the FCQ  401 . Therefore, the FCQ  401  contains no nose, unlike the nose  209 ,  302  present in prior art silencers  202 ,  304  ( FIGS. 2B ,  3 B). 
         [0052]      FIG. 4C  depicts an end view of the FCQ  401  and the perforated metal casing  453  that encloses the insulating material  454  of the baffle  409 .  FIG. 4C  also shows the casing  451  of the silencing portion  404  of the FCQ  401  and the casing  452  of the plenum portion of the FCQ  401 . 
         [0053]      FIG. 4D  depicts a cross-sectional view of the insulating material  454  that comprises the baffle  409  of the silencing portion  404  of the FCQ  401 .  FIG. 4D  also shows the casing  451  of the silencing portion  404  of the FCQ  401  and the casing  452  of the plenum portion of the FCQ  401 . 
         [0054]      FIGS. 5A-5E  illustrate an embodiment of the invention wherein the baffle  502  of the silencing portion  503  of the FCQ  501  flares outward in a “tail”  504 . This tail  504  allows the expanding air that is traveling down the air pathway  505  to maintain a constant pressure. This is because the increased cross-sectional area of the tail portion  504  of the FCQ  501  provides additional space for the expanding air to occupy, thus preventing a buildup of pressure within the FCQ  501 . 
         [0055]      FIG. 5C  depicts an end view of the FCQ  501  and the perforated metal casing  553  that encloses the insulating material  554  of the baffle  502 .  FIG. 5C  also shows the casing  551  of the silencing portion  503  of the FCQ  501  and the casing  552  of the plenum portion of the FCQ  501 . 
         [0056]      FIG. 5D  depicts a cross-sectional view of the insulating material  554  that comprises the baffle  502  of the silencing portion  503  of the FCQ  501 .  FIG. 5D  also shows the casing  551  of the silencing portion  503  of the FCQ  501  and the casing  552  of the plenum portion of the FCQ  501 . 
         [0057]      FIGS. 6A-6E  illustrate an embodiment of the invention with a high-frequency splitter  602  placed in the air pathway  603  of the FCQ  601 . The high-frequency splitter  602  scatters high-frequency sound waves that would otherwise pass relatively unobstructed through the air pathway  603  due to the “beaming” effect of high-frequency sound. The scattered high-frequency sound waves will therefore tend to impact the baffle  605  directly or bounce off the casing  604  and then into the baffle  605 , which will attenuate the sound. 
         [0058]      FIG. 6C  depicts an end view of the FCQ  601  and the perforated metal casing  653  that encloses the insulating material  654  of the baffle  605 .  FIG. 6C  also shows an end view of the high-frequency splitter  602 .  FIG. 6C  also shows the casing  651  of the silencing portion of the FCQ  601  and the casing  652  of the plenum portion of the FCQ  601 . 
         [0059]      FIG. 6D  depicts a cross-sectional view of the insulating material  654  that comprises the baffle  605  of the silencing portion of the FCQ  601 .  FIG. 6D  also shows the casing  651  of the silencing portion of the FCQ  601  and the casing  652  of the plenum portion of the FCQ  601 . 
         [0060]      FIGS. 7A-7E  depict an embodiment of the invention wherein the air pathway  702  of the FCQ  701  is angled or curved, thus minimizing or eliminating the line-of-sight pathway from the centrifugal fan  703  to the discharge outlet of the FCQ  701 . This elimination of the line-of-sight pathway will likewise minimize the high-frequency noise emitted by the centrifugal fan  703  and prevent high-frequency sound waves from traveling down the air pathway  702  unobstructed. The silencing portion of the FCQ  701  can be up to five feet in length, or as little as three feet or less, depending on the application and design parameters. 
         [0061]      FIG. 7C  depicts an end view of the FCQ  701  and the perforated metal casing  753  that encloses the insulating material  754  of the angled top baffle  704 .  FIG. 7C  also shows the casing  751  of the silencing portion of the FCQ  701  and the casing  752  of the plenum portion of the FCQ  701 . 
         [0062]      FIG. 7D  depicts a cross-sectional view of the insulating material  754  that comprises the top and bottom baffles  704 ,  705  of the silencing portion of the FCQ  701 .  FIG. 7D  also shows the casing  751  of the silencing portion of the FCQ  701  and the casing  752  of the plenum portion of the FCQ  701 . 
         [0063]      FIGS. 8 and 9  depict an additional embodiment of a silencer  801  based on that of  FIG. 7 , except that it further includes an integrated condensate diverter  803  at the inlet to the silencer  801  rather than a rounded nosing or endplate on the baffle  807 . Because the inlet to this silencer  801  has no blunt obstructions, it can efficiently mate with any HVAC component having standard dimensions. It does not have to be designed, for example to mate with the outlet of a single centrifugal fan as shown in  FIG. 7B  but could mate with a fan coil unit having two or more fans, an axial fan, etc. 
         [0064]    The construction details for this silencer  801  will depend on the application and environment in which the system is being installed. For example, in a standard commercial application the casing  805  may be galvanized sheet metal. In such an installation the condensate diverter  803  will typically also be of galvanized sheet metal without perforations, riveted to the silencer walls, the joints being sealed with commercial sealant. The trailing edge of the condensate diverter  803  meets the leading edge of the perforated sheet metal making the lower baffle  807 . The condensate diverter  803  may be fastened to the lower baffle  807 , but it is generally sufficient to have a folded joint. The trailing edge of the lower baffle  807  terminates adjacent to the outlet of the silencer  801 , being fastened to the floor of the silencer  801  with rivets, sheet metal screws, tack-welds or other similar fastening systems. 
         [0065]    In  FIG. 8  the silencer  801  is shown connected to a fan coil assembly  811 , which includes coils  813  and a drip pan  809  to collect condensate from the coils  813 . The leading edge of the condensate diverter  803  may protrude from the front of the silencer  801  as shown in both  FIG. 8  and  FIG. 9  so that condensation dripping down from the condensate diverter  803  is diverted back to the drain slots in the water coil, to the existing drip pan  809 . Alternatively, one could design the condensate diverter  803  to be entirely enclosed by the silencer  801  and provide a separate drip pan below the condensate diverter  803 . 
         [0066]    Exemplary dimensions for this silencer embodiment are shown in  FIG. 9 . Specifically, this embodiment is shown for a standard 36″ L×21″ W×9″ H duct. The condensate diverter  803  is 8.344″ long and is oriented at an angle of 35° to the lower panel of the casing  805 . The lower baffle  807  and upper baffle  815  are parallel to one another and spaced apart by 3.5″. The lower baffle  807  and upper baffle  815  are typically fabricated from perforated sheet metal or wire mesh, and are filled with sound-absorbing media. The type of media used, the density and binding agents will depend on the customer&#39;s specifications, building codes and the application and may include for example, matted or randomly arranged fibreglass or rockwool insulation. Such design parameters are known in the art. 
         [0067]    The angle of the nosing and the length were optimized during design and testing to ensure that the condensation carryover would be effectively reduced without creating too much pressure drop. By increasing the length of the condensate diverter  803  one could effectively catch more condensate carryover but the length of the silencer would be increased. In the application of  FIG. 9  it was necessary to keep the entire length less than 36″ so sound testing was performed to optimize the design. 
         [0068]    The diagonal orientation of the baffles  807 ,  815  provides a longer path for sound to travel along the baffle surfaces for a given a silencer length, resulting in greater sound reduction for a given silencer length. Increasing the gap between the baffles  807 ,  815  will result in lower losses, though it will result in less noise reduction. In the embodiment of  FIG. 9  there is no line-of-sight path through the silencer when the leading edge of the lower baffle  807  is higher than the trailing edge of the upper baffle  815 . Increasing the degree of overlap between the leading edge of the lower baffle  807  and the trailing edge of the upper baffle  815  when viewed from the inlet of the silencer will also increase the degree of noise reduction. 
         [0069]    In this particular embodiment, integrating the silencer baffles  807 ,  815  and condensate diverter  803  allowed the combined unit to be reduced in length by 8″. Reducing the length saves material, and also allows a silencer and condensate diverter to be installed in a tighter location. If space constraints forced one to go without a condensate diverter then downstream components could deteriorate due to rust and mold, and air quality would suffer. 
         [0070]    Integrating the non-line-of-sight concept with the flat, condensate diverter nosing, effectively reduced the noise levels as well as reducing the amount of condensate carryover. Sound power levels of fan coil units were reduced as was condensate carryover, without reducing flow performance. 
         [0071]    Silencers for fan coil units are available on the market but they do not offer integral condensate diverting sections. There are condensate diverting sections which are occasionally used in the industry but these are only available separate from the silencer. Typically, the trailing edge of commercially available condensate diverting sections do not line up at all with the leading edge of commercial silencers, so there is a great deal of turbulence and resulting air flow losses. Even if the two components did mate effectively, this would result in a longer component than the integral design of the invention, and it would not provide an optimized solution. That is, the integral design can be tested in a lab and optimized for design parameters. In contrast, combining separate silencer and condensate diverter sections that have been optimized independently will not yield the same performance. 
         [0072]    While this invention has been described with reference to the structures and processed disclosed, 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.