Patent Publication Number: US-7591633-B2

Title: Centrifugal blower for air handling equipment

Description:
BACKGROUND OF THE INVENTION 
   Motor driven centrifugal blowers for air handling equipment, such as heating, ventilating and air conditioning (HVAC) systems are well known. A typical air handling blower includes a scroll-like housing within which is mounted a centrifugal blower wheel or impeller of a selected diameter and axial length and wherein the housing is adapted or “sized” to operate efficiently with a particular blower wheel or impeller. 
   However, there are many applications of air handling equipment wherein it is desirable to select the impeller size to accommodate a particular airflow requirement, impeller rotational speed and static or blower discharge pressure requirement, or a change in such requirements. Such performance requirements or desiderata in the equipment market may dictate that many different size blower wheels and associated blower housings be designed and fabricated to meet particular performance requirements of the blower application. Of course, such a situation increases the costs associated with providing products to suit each blower application. 
   Accordingly, there has been a continuing need and desire to reduce the costs and product complexity associated with providing various blower wheel sizes and associated blower housings which will accommodate the various specific wheel or impeller sizes while meeting the performance requirements of a blower, without adverse effects of increased noise produced by the blower, as well as other parameters of blower performance and operation known to those skilled in the art. In accordance with the present invention, it has been discovered that a particular configuration of blower housing in combination with a particular range of centrifugal impeller sizes provides for operation without sacrificing blower performance and while maintaining reduced noise levels. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved air handling blower for use, in particular, with heating, ventilating and air conditioning (HVAC) equipment wherein a blower housing accommodates blower wheels or impellers of selected different sizes and performance capability while maintaining desirable performance parameters and acoustic emission or “noise” levels. 
   In accordance with one aspect of the present invention, a combination of a centrifugal blower scroll type housing and a centrifugal blower wheel or impeller is provided wherein an impeller providing for high airflow and/or static pressure, in combination with the blower housing is such that the housing air inlet port or orifice has a diameter that is no smaller than the inner diameter of the blades of the largest impeller that the housing will accommodate while the blower housing inlet port or orifice diameter is also no larger than the outer diameter of the smallest impeller or wheel that the housing will accommodate. 
   Accordingly, the invention contemplates the provision of an air handling blower having a scroll-like housing with an air inlet port or orifice which will accommodate centrifugal blower wheels or impellers of various sizes wherein the outer diameter of the smallest wheel is generally no less than the inner diameter of the largest wheel. 
   Still further, in accordance with the invention, a centrifugal air handling blower is provided wherein a blower housing having a somewhat spiral or scroll-like air flowpath configuration includes an improved blower wheel cutoff edge configuration having first and second ends and a midsection operable to accommodate a blower wheel or impeller of a selected range of outside diameters wherein the efficiency of the blower is improved, as compared with conventional centrifugal air handling blowers, and blower acoustic emissions are reduced for the same range of blower wheel diameters. 
   Accordingly, an improved blower configuration is provided by the invention wherein, for a particular size of scroll-like blower housing, a range of blower impeller sizes may be provided wherein such impellers have a particular range of diameters which may be used with the blower housing without reduction in efficiency or increase in noise generated through the use of impellers of various sizes. Still further, the combination of a scroll-like blower housing and range of blower impeller sizes in accordance with the invention provides for obtaining a predetermined air flow rate and discharge pressure required for a blower application at a rotational speed that corresponds to an efficient operating point for the blower drive motor. This flexibility is particularly advantageous for applications utilizing so-called PSC (permanent split capacitor) motors which have an efficiency peak at about ninety percent of synchronous speed. The efficiency of such motors tends to deteriorate at rotational speeds which deviate from the ninety percent of synchronous speed value. 
   Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the invention, together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view, partially cutaway, illustrating air handling equipment utilizing an improved air handling blower of the present invention; 
       FIG. 2  is an exploded perspective view of an improved air handling blower in accordance with the invention; 
       FIG. 3  is a section view taken generally along the line  3 - 3  of  FIG. 2  and illustrating a blower wheel or impeller having a first or maximum diameter; 
       FIG. 4  is a section view similar to  FIG. 3  but showing an impeller of minimum outside diameter mounted within the same blower housing; 
       FIG. 5  is a detail section view taken generally along the line  5 - 5  of  FIG. 2  showing the relationship between the blower cutoff edge and the outside diameter of an impeller of maximum diameter; 
       FIG. 6  is a view taken along the same line as  FIG. 5  and showing the relationship between the cutoff edge and the outside diameter of an impeller of minimum diameter; 
       FIG. 7  is a section view taken generally along line  7 - 7  of  FIG. 2 ; and 
       FIG. 8  is an end view of a blower and a cutoff. 
   

   DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
   In the description which follows, like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat generalized form in the interest of clarity and conciseness. 
   Referring to  FIG. 1 , there is illustrated a heating, ventilating and air conditioning unit (HVAC), generally designated by the numeral  10 , characterized by a generally rectangular cabinet  12  having a bottom wall  14  defining an air inlet opening  16  and a top wall  18  defining an air outlet opening  20 . The unit  10  may comprise a so-called air handler including an air conditioning evaporator coil  22  disposed therein in the flowpath of air passing from the inlet  16  to the outlet  20 . An air handling blower in accordance with the invention is disposed in the cabinet  12  and generally designated by the numeral  24 . The blower  24  includes a somewhat conventional electric drive motor  26  mounted on a blower housing in accordance with the invention and generally designated by the numeral  28 . Blower housing  28  is characterized by a generally spiral or scroll-like configuration which may be substantially like that described and claimed in U.S. published patent applications nos. US2004/0253098A1, US2004/0253099A1 and US2004/0253101A1, all to Stephen S. Hancock and all assigned to the assignee of the present invention. The subject matter of the above-identified published patent applications is incorporated herein by reference. 
   Referring further to  FIG. 1 , and  FIG. 2 , the centrifugal blower  24  also includes a centrifugal blower wheel or impeller  30  disposed in the housing  28 ,  FIG. 2 . Impeller  30  is of generally conventional construction, comprising a so-called squirrel cage type impeller with a central transverse disc-like support member  32  including a hub  32   a,  see  FIG. 7 , and plural circumferentially spaced, generally radially outwardly projecting impeller blades  34 . Blades  34  may be forward or backward curved and are illustrated as backward curved with respect to the direction of rotation about axis  30   x,    FIGS. 2 ,  3 ,  4  and  7 , which direction is indicated by arrow  30   y  in  FIG. 7 . Impeller  30  is adapted to be drivenly connected to drive motor  26 , which motor is provided with a shaft  26   a  drivingly engaged with hub  32   a,    FIG. 3 , and motor  26  also includes a support bracket  36  adapted for mounting the motor on the blower housing  28  in a selected position on one of opposite sides thereof. 
   Blower housing  28  is provided with opposed air inlet ports or orifices  40  and  40   a,    FIGS. 3 and 4 . Ports or orifices  40  and  40   a  are preferably generally circular in configuration and are provided on opposite sides of the blower  28 , as shown. Accordingly, the dimensions which define the ports  40  and  40   a,  and the air flowpath area of the ports, are the respective port diameters d 40  and d 40   a,    FIG. 3 . Blower housing  28  includes opposed housing members  28   a  and  28   b  which may be constructed as described in the above-referenced published patent applications and which jointly define a blower air outlet port  42  delimited by a generally rectangular perimeter flange  44 , see  FIGS. 2 and 7 . Flange  44  is adapted to assist in supporting blower  24  at a transverse wall  31  formed in cabinet  12 , as illustrated in  FIG. 1 , and having a port or opening  31   a  aligned with blower outlet or discharge port  42 . 
   As shown in  FIG. 7 , blower impeller  30  is provided with circumferentially spaced, preferably backward curved blades  34 , although other arrangements of blades in a generally centrifugal blower wheel or impeller may be provided while enjoying the benefits of the present invention.  FIG. 7  also illustrates how an outer peripheral wall  33  of blower housing  28  is disposed generally at an increasing radius with respect to axis  30   x  from a blower cutoff edge  39 ,  FIG. 7 , in a counter-clockwise direction from the cutoff edge, to an air discharge duct portion  41  of the blower housing disposed just upstream of or prior to outlet port  42 . However, blower housing  28  is also, preferably, of a geometry as described in the afore mentioned published patent applications incorporated herein by reference. The interior airflow space  28   s  of blower housing  28 ,  FIGS. 3 ,  4  and  7 , is arranged to provide a substantially constant increasing cross-sectional flow area between cutoff edge  39  and the air discharge portion  41  of the blower housing. 
   Referring now to  FIG. 3 , impeller  30  is further illustrated with respect to its relationship to the inlet port  40  and the opposing coaxially aligned inlet port or orifice  40   a.  In fact, blower housing  28  may be substantially symmetrical about a plane defined by a parting line  28   p,    FIGS. 3 and 4 . It will be noted in  FIG. 3  that the inner or inside diameter d 30  of impeller  30 , defined as the diametral distance between the radially innermost edges  34   d  of impeller blades  34 , is approximately equal to the diameters of the orifices or ports  40  and  40   a.  For the configuration of a particular blower housing  28  constructed in accordance with the present invention an impeller  30  having an outside diameter D 30  would be closely adjacent the cutoff edge  39 , see  FIG. 5  also, particularly at the opposed lateral edges  39   c  and  39   d.  In other words, the radially outermost edges  34   e  of impeller blades  34  would be at their closest proximity to the cutoff edge  39 , as shown in  FIG. 5 . Cutoff edge  39  preferably forms an elliptical shape, as taught by published patent application US 2004/0253099A1. 
   still further, a first clearance distance  39   e  between the outside diameter D 30  of the impeller  30  and the cutoff edge  39  at cutoff edge locations  39   c  and  39   d  ranges, preferably, from a minimum of 0.5% of the impeller outside diameter to a maximum of 5.0% of the impeller outside diameter while a second distance, measured generally at the midpoint of the elliptical cutoff edge  39 , indicated by  39   a , is greater than the first distance. In one preferred embodiment, the first distance  39   e  is approximately 2.0% of the impeller diameter D 30  while the second distance  39   a  is approximately 6.0% of the impeller diameter D 30 . Of course, in accordance with the teaching of the above-identified published patent application, the edge  39  is symmetrical and continuous about mid point  39   a , forming, preferably, an elliptical shape. The cutoff portion of the blower housing  28  is further defined by face  46  which is formed as an area between cutoff edge  39  and a so-called discharge side edge  47 ,  FIG. 5 . Viewing  FIG. 5 , the cutoff edge  39  includes a first end portion ranging between first and second positions  39   g  and  39   h , a second end portion ranging between third a fourth position  39   j  and  39   k , and a cutoff edge midsection portion extending between the first and second end portions. The cutoff edge midsection between positions  39   h  and  39   k  forms an acoustic emissions reduction portion of the cutoff edge where the elliptical cutoff edge  39  has a first flattened arc relative to the axis  30   x  promoting quieter air flow, whereas the portions on either side of the cutoff edge midsection portion have a second sharper arc relative to the axis  30   x  inhibit recirculation of air and promote stability in operation of the blower. 
   Referring now to  FIG. 4 , there is illustrated the blower housing  28  wherein the impeller  30  has been replaced by an impeller  50  having the same general construction as the impeller  30  and rotatable about axis  30   x,  but being of smaller outside and inside diameters, respectively. Blower impeller  50  is provided with plural circumferentially spaced blades  54  secured also to a center support or disc  52  including a motor shaft receiving hub  53 , and wherein impeller  50  has an inner or inside diameter d 50  defined as the diametral distance between opposed ones of the inner blade edges  54   d  and an outer or outside diameter D 50 , defined as the diametral distance between opposed ones of radially outer edges  54   e  of blades  54 . In the arrangement of  FIG. 4  the outer diameter D 50  is approximately equal to the diameters of the orifices or air inlet ports  40  and  40   a.    FIG. 6  illustrates the relationship between the cutoff edge  39  and the impeller  50  wherein, of course, a greater distance is provided between the edge  39  and the radially outermost edges  54   e  of the impeller blades. Although the view of  FIGS. 5 and 6  are taken generally from line  5 - 5  of  FIG. 2 , impellers  30  and  50  are also shown in section for illustrative purposes. 
   Accordingly, as shown and described, the diameters of the blower inlet ports or orifices  40  and  40   a  are generally no smaller than the inside diameter d 30  of the largest diameter impeller or wheel  30  and generally no smaller than the outside diameter D 50  of the smallest diameter wheel or impeller  50 . In order to meet these conditions, the outside diameter D 50  of the impeller  50  is no smaller than the inside diameter d 30  of the impeller  30 . Still further, the cutoff edge  39  is configured such that the radial clearance provided for the largest diameter impeller to be provided is the smallest and typically is about 1.0% to 2.0% of the impeller outside diameter. With these relationships the improved cutoff provided by the curved edge  39  still performs its intended purpose when the blower  24  is operating with the smallest diameter wheel or impeller, such as the impeller  50 . 
   The construction and operation of a blower assembly, such as described herein is believed to be within the purview of one skilled in the art of air handling blowers for HVAC equipment and the like. Conventional engineering materials, including those described in the above-mentioned published patent applications, may be used to fabricate the blower housing  28  as well as the impellers  30  and  50 . Moreover, those skilled in the art will also appreciate that impellers of respective inside and outside diameters in a range between the corresponding diameters of the impellers  30  and  50  may be utilized in conjunction with a housing such as the housing  28  without loss of blower performance and while enjoying the benefits of the invention. Thus, by providing a blower having the combination of a housing constructed in accordance with the invention as described herein and a range of impeller sizes from the diameters of the impeller  30  to the diameters of the impeller  50 , various blowers may be constructed having airflow, discharge pressure and acoustic emission characteristics which may suit particular applications without requiring that blower housings of different sizes be furnished. In this way manufacturing complexity is reduced without sacrificing product performance or operating efficiency. 
     FIG. 8  shows an end on view of a blower  1020  and cutoff  1026 . The cutoff  1026  can be seen to have a face  1048  and a non-linear edge  1050  which are separated from a periphery  1052  of the blower  1020  by a varying distance  1053 . The cutoff edge  1050  is the demarcation separating discharge airflow from recirculation. The cutoff face  1048  is formed as an area between a discharge side edge  1049  of the cutoff edge  1048  and a entrance side edge  1051  of the cutoff edge  1048 . A particular cutoff angle, θ, defined as an angle between a line from a particular point on the cutoff edge  1048  to the axis  1012  and an arbitrary reference plane where the reference plane does not include the line. 
   The edge  1048  has a first end  1054 , a midsection  1056  and a second end  1058 . The area around the midsection  1056  forms an acoustical reduction portion  1061  promoting quieter airflow, whereas the areas around the first and second ends  1054 ,  1058  form efficiency enhancing portions  1063  inhibiting recirculation and promoting stability. A radial distance from the periphery  1052  of the blower is a first distance  1060  at the first and second ends  1054 ,  1058  and a second distance  1062  at the midsection  1056 . In the preferred embodiment, the second distance  1062  is greater than the first distance  1060 . Thus, the midsection  1056  is farther from the periphery  1052  than the first and second ends  1054 ,  1058 , and distance between the cutoff edge  1050  and the periphery  1052  varies continuously therebetween. 
   The edge  1050  can be described as being symmetrical and continuous about a midpoint  1064  with the result that the edge  1050  forms an elliptical shape. In the acoustical reduction portion  1061 , this elliptical shape has a first flattened arc relative to the axis  1012 . In the efficiency enhancement portion  1063 , the elliptical shape has a second sharper arc relative to the axis  1012 . 
   Although a preferred embodiment of the invention has been described in detail herein those skilled in the art will recognize that various substitutions and modifications may be made without departing from the scope and spirit of the appended claims.