Abstract:
The invention concerns a fan assembly ( 10, 100 ) which includes a vertical axis wind turbine (VAWT) ( 12, 102 ) which is coupled to an air extraction or air supply fan ( 14, 146 ). The VAWT is located above and is coupled coaxially to the fan. The fan assembly also includes an auxiliary turbine ( 36, 140 ) to provie start-up torque to initiate rotation of the VAWT. The VAWT is typically a Darrieus or Gyromill-type turbine and the auxiliary turbine is typically a Savonius-type turbine. In the preferred embodiments, the fan assembly includes a rotational speed governor to avoid damage to the turbine and/or fan in high winds.

Description:
BACKGROUND TO THE INVENTION  
         [0001]    This invention relates to a fan assembly.  
           [0002]    An important application of the fan assembly of the invention is extraction of air from a building space or from ducting. In a specific application, the fan assembly may be mounted in or on the roof of a building to extract air from the building space below or from ducting in the building. A known fan assembly which is currently used in such applications is the so-called “Whirlybird”, the main component of which is essentially a Savonius drag-type turbine. The turbine serves both to catch the wind and to extract air. Although fan assemblies of this type are in widespread use, they product a negligible pressure differential and are accordingly often unable to overcome the aerodynamic resistance to air flow through the space or ducting.  
         SUMMARY OF THE INVENTION  
         [0003]    According to the present invention there is provided a fan assembly comprising an upright axis wind turbine coupled to a separate, upright axis air extraction or air supply fan to drive the fan.  
           [0004]    In the preferred embodiment, there is a vertical axis wind turbine coupled coaxially, with or without intermediate gearing, to the fan. The preferred vertical axis wind turbine is a multi-blade Darrieus or Gyromill-type rotor with symmetrical or cambered aerofoil-profile blades. Start-up torque for the turbine may be provided by an auxiliary helical drag-type turbine, typically a Savonius-type turbine, on the axis of the main turbine.  
           [0005]    Preferably the fan itself is a vertical axis, single-inlet fan the impeller of which has backward-curved aerofoil section fan blades.  
           [0006]    According to a preferred feature, the assembly includes a rotational speed governor.  
           [0007]    Other preferred features of the fan assembly are set forth in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:  
         [0009]    [0009]FIG. 1 shows a diagrammatic side elevation of a fan assembly according to this invention;  
         [0010]    [0010]FIG. 2 shows a cross-section at the line  2 - 2  in FIG. 1;  
         [0011]    [0011]FIG. 3 shows a cross-section at the line  3 - 3  in FIG. 1;  
         [0012]    [0012]FIG. 4 shows a cross-section at the line  4 - 4  in FIG. 3;  
         [0013]    [0013]FIG. 5 shows a cross-section at the line  5 - 5  in FIG. 3;  
         [0014]    FIGS.  6 ( a ) and  6 ( b ) show alternative turbine blade aerofoil sections;  
         [0015]    [0015]FIG. 7 shows a cross-section at the line  7 - 7  in FIG. 1;  
         [0016]    [0016]FIG. 8 shows a diagrammatic side elevation of a fan assembly according to a second embodiment of the invention;  
         [0017]    [0017]FIG. 9 shows a cross-section at the line  9 - 9  in FIG. 8;  
         [0018]    [0018]FIG. 10 shows a cross-section at the line  10 - 10  in FIG. 8;  
         [0019]    [0019]FIG. 11 shows a side elevation of a turbine blade as used in the embodiment of FIG. 8;  
         [0020]    [0020]FIG. 12 illustrates the internal structure of the turbine blade seen in FIG. 11;  
         [0021]    FIGS.  13 ( a ) and  13 ( b ) illustrate a connection between a turbine blade and a spoke in the embodiment of FIG. 8;  
         [0022]    [0022]FIG. 14 shows a detail of the fan assembly mounting in the embodiment of FIG. 8;  
         [0023]    FIGS.  15 ( a ) and  15 ( b ) show plan views of modified top and bottom turbine blade spokes respectively;  
         [0024]    [0024]FIG. 16 shows a typical cross-section of a modified turbine blade spoke as illustrated in FIG. 15( a ) or  15 ( b );  
         [0025]    [0025]FIG. 17 illustrates a handbrake which can be used in the embodiment of FIG. 8;  
         [0026]    [0026]FIG. 18 shows a side elevation of the auxiliary turbine of the embodiment of FIG. 8; and  
         [0027]    [0027]FIG. 19 shows a typical horizontal cross-sectional view of the auxiliary turbine of FIG. 18. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0028]    The fan assembly  10  seen in FIG. 1 has, as its major components, a vertical axis wind turbine (VAWT)  12 , an extraction fan  14  arranged coaxially with the VAWT and a round cylindrical duct  16 . As shown in FIG. 3, the fan  14  is mounted on the duct  16  which is in use secured to a roof  18  with the interior of the duct in communication with a space  20  beneath the roof from which air is to be extracted. The broken lines in FIG. 3 indicate an alternative arrangement in which the duct  16  communicates with an air duct  22  beneath the roof.  
         [0029]    The VAWT includes three vertically oriented, aerofoil section turbine blades  26  connected to one another at their lower ends by spars  24 . In FIGS. 2 and 6( a ) the blades  26  have a cambered aerofoil section while in the alternative configuration seen in FIG. 6( b ) the blades have a symmetrical aerofoil section. At an elevated position, the three blades are connected to one another by spars  28 . From the centre of each spar  28  a member  30  extends radially towards the axis  32  of the VAWT.  
         [0030]    The inner ends of the members  30  are secured to a central shaft  34  on which an auxiliary turbine  36  is mounted between the main turbine blades  26 , coaxially with the VAWT  12 .  
         [0031]    The auxiliary turbine  36  includes a stack of blades  38  which are of semi-circular section and arranged in pairs  40 . As shown in FIG. 7, the inner ends of the individual blades in each pair, at each level, are supported by a rod  42  extending diametrically through the shaft  34  while their outer ends are supported by radial extensions  44  of the rod. As will be apparent from FIGS. 1 and 2, the blade pairs  40  are progressively, angularly off-set from one another, and the radius of curvature of the blades decreases, with increasing height in the stack.  
         [0032]    The fan  14  includes a series of angularly spaced blades  46  forming an impeller  48 . The lower edges of the blades  46  are secured to an annular base plate  50 . The base plate  50  is connected to a tubular shaft  52  bolted through brackets  54  to a plate  55  to which the shaft  34  is secured and on which the spars  24  are mounted. The base plate  50  and accordingly the impeller  48  are thus rotationally fast with the VAWT. As illustrated in FIG. 3, the shaft  52  is supported rotationally in bearings  56  relative to a central stub shaft  58  welded at  60  to a spoked frame  62  spanning across the interior of the duct  16 .  
         [0033]    It will be understood that the VAWT  12  and auxiliary turbine  36  extend above the roof  18  and are exposed to ambient air movements. The auxiliary turbine  36  provides start-up torque to initiate rotation of the VAWT. In this regard it will be noted that the progressive angular offset of the various blade pairs  40  ensures that air movement is picked up by the auxiliary turbine irrespective of the direction of that movement.  
         [0034]    The rotation of the VAWT is transferred directly to the fan impeller  48  which accordingly rotates at the same angular speed as the VAWT. Air is drawn axially out of the space  20  (or the duct  22 ) and is expelled outwardly by the impeller  48 .  
         [0035]    The use of a VAWT is an important feature of the invention. A turbine of this type has been shown to be tolerant of blustery wind conditions which are typically encountered in built-up areas. Added to this, it is recognised that efficient air extraction is dependent on the tip speed of the fan blades and hence on the rotational speed of the fan impeller. A Darrieus lift-type VAWT as described above can be shown to produce rotational speeds, in similar wind conditions, which are substantially higher than those achievable with a corresponding drag-type turbine. As a matter of design it will be understood that the VAWT will n practice be matched to the fan to achieve the best air extraction efficiency.  
         [0036]    Although not shown in the drawings, it is also possible to increase the tip speed of the impeller blades by including step-up gearing between the VAWT and the fan impeller, although it is recognised that a gearbox may itself cause some overall loss of efficiency.  
         [0037]    Referring to FIG. 4, it will be seen that the impeller blades  46  are backwardly curved. By this is meant that for the indicated direction of rotation of the impeller, each blade  46  curves outwardly and away from the direction of forward motion. This features reduces the radial component of the motion which is imparted to the extracted air. Also, with backwardly curved impeller blades the impeller presents a minimal obstruction to the flow of air through the fan, and accordingly allows an acceptable air flow, induced merely by buoyancy of warm air relative to cool air in the space  22 , to take place when there is insufficient air movement to rotate the VAWT at a meaningful speed.  
         [0038]    In order to reduce the overall mass and hence rotational inertia of the VAWT and fan, it is preferred that these components, and in particular their blades, be made of aluminium. Another possibility under consideration is a lightweight balsa wood frame covered by a thin skin of appropriately tough material.  
         [0039]    The cambered aerofoil profile seen in FIG. 6( a ) is in general preferred to the symmetrical design of FIG. 6( b ) since the cambered shape can be expected to provide some initial start-up torque to assist the auxiliary turbine to initiate rotation of the VAWT.  
         [0040]    Referring to FIG. 3 it will be seen that members  60  are suspended on hinges  62  from a conical inlet  64  of the impeller  48 . The members  60  carry respective brake shoes  66  at their ends. During rotation of the turbine and fan impeller, the members  60  will swing outwardly as indicated by the arrows  68 , the extent of such swinging movement being dependent on the rotational speed and hence the centrifugal force. In high winds where excessive rotational speeds would otherwise be generated, the brake shoes  66  make frictional contact with the internal surface of the duct  16  to govern the rotational speed to within acceptable limits.  
         [0041]    The fan assembly in the example described above serves an air extraction function. It will however be appreciated that a fan assembly according to the invention could also be used in an air supply mode. In this case, it would be appropriate to replace the illustrated fan impeller  48  with an axial or mixed flow impeller.  
         [0042]    Referring to FIG. 5 it will be seen that the duct  16  is provided with handles  70  for carrying the fan assembly or at least the lower components thereof.  
         [0043]    In the embodiment described above and illustrated in FIGS.  1  to  7  the auxiliary turbine has a stepped helical construction. In other embodiments of the invention, one of which is described below, the auxiliary turbine can have a continuous helical shape.  
         [0044]    FIGS.  8  to  19  illustrate a second embodiment of fan assembly, indicated generally by the numeral  100 , according to the invention. The basic components of the assembly are the same as those of the first embodiment  10  described above. In this case the VAWT  102  has only two diametrically opposed turbine blades or wings  104  as opposed to the three blade configuration of the first embodiment. Each of the blades has a cambered aerofoil shape similar to that illustrated in FIG. 6( a ). As illustrated in FIG. 11, each blade is tapered from top to bottom. Referring specifically to FIG. 12, each blade  104  includes an internal framework consisting of an internal spar  106 . 1 , rods  106 . 2  and  106 . 3  at the leading and trailing edges rerspectively and a series of internal braces  106 . 4 . The spar, rods and braces are made of carbon fibre. The internal framework is covered by woven glass fibre cloth.  
         [0045]    The turbine blades  104  are supported at upper and lower positions by radial spars or spokes  108 ,  110  respectively. Each spoke includes two aluminium rods  112 ,  114 . As shown in FIG. 15( a ) the rods  112  of the upper spokes are parallel to one another. As shown in FIG. 15( b ), the rods  114  of the lower spokes  110  are slightly convergent. For improved aerodynamic efficiency, the pairs of rods  112 ,  114  can be clad in elliptical cladding structures  116  as illustrated in FIG. 16. The spokes  108 ,  110  are connected to a central shaft  118  by brackets  120 , 122 .  
         [0046]    In the first embodiment, the turbine blades  26  are rigidly connected to the ends of their supporting spars. However in this embodiment, the turbine blades  104  are connected to the ends of the spokes  108 ,  110  by means of hinges  124  which are illustrated in some detail in FIGS.  13 ( a ) and  13 ( b ). A holed bracket  126  projects inwardly from a transverse plate  128  secured to each blade at each connection point. Projecting outwardly from a transverse plate  130  at the outer end of each spoke is a corresponding holed bracket  132 . The brackets  126 ,  132  are connected pivotally to one another by means of a bolt  134 . Acting between the plates  128 ,  130  at a position to one side of the pivot point, i.e. the axis of the bolt  134 , is a compression spring  136 . A stop member  138  in the form of a bolt is attached to the plate  130  on the other side of the pivot point and extends towards the plate  128 . In the position shown in FIG. 13( a ) the spring  136  urges the plate  128  into abutment with the end of the stop member  138 . The length of the stop member is set such that in this position of abutment, the associated turbine blade  104  is pitched for optimal aerodynamic efficiency, and the spring tension is selected to ensure that this pitch is maintained during normal operation of the turbine.  
         [0047]    The pivot point  134  is off-set relative to the centre of gravity of the turbine blade such that with increasing blade velocity the blade has a tendency to pitch negatively as a result of increased centrifugal force acting on it At a predetermined blade velocity, the bias of the spring  136  is overcome and the spring is compressed, as illustrated in FIG. 13( b ), allowing the blade to assume a negative pitch. This reduces the aerodynamic efficiency of the blade. The negative pitch of the blade increases with increasing rotational velocity of the VAWT until eventually the situation is reached that the blade stalls aerodynamically. The VAWT is accordingly governed to a maximum safe rotational velocity.  
         [0048]    It will be understood that the hinged nature of the turbine blades provides the VAWT with an automatically operating aerodynamic rotational speed governor which replaces the centrifugal braking arrangement of the first embodiment.  
         [0049]    It will also be noted in FIG. 13( a ) that each turbine blade is reinforced by transverse members  140  providing support for the plate  128 .  
         [0050]    In the second embodiment, the Savonius-type auxiliary turbine of the first embodiment, having the stepped helical construction described above, is replaced by a Savonius-type auxiliary turbine  140  of continuous helical design. Referring to FIG. 18, the auxiliary turbine  140  includes an internal frame  142 , of lightweight aluminium or glass-reinfroced plastic material, over which is stretched a skin of wind-impermeable fabric  144 . As shown in FIG. 19 the internal frame has a similar configuration to that used in the first embodiment.  
         [0051]    The fan  146  of the second embodiment is generally similar to that of the first embodiment and its components are preferably of aluminium or glass-reinforced plastics  
         [0052]    As illustrated in FIGS. 8 and 14, the fan assembly  100  includes an outer frustoconical windshield  148  which surrounds the fan  146  and shields it from ambient wind movements. The windshield  148  is mounted on a ring  150  supported by braces  152 . Foot support plates  154  project transversely from the ring  150  to provide platforms for personnel to stand on during maintenance or inspection of the fan assembly. In addition the ring also provides a convenient structure for lifting the assembly when necessary and serves as a bumper to protect the assembly during transportation and handling. In addition the ring could be used to support a volute casing to serve as an air supply plenum in those instances where the fan assembly of the invention is used in an air supply mode as opposed to air extraction mode.  
         [0053]    Referring to FIG. 14, the fan is surmounted by an upper plate  156  which is of somewhat greater diameter than the fan impeller itself, to prevent ingress of rainwater through the fan. The duct  160  which communicates with the space  162  from which extraction is to take place is typically of mild steel and is provided with a taper to optimise air flow into the fan.  
         [0054]    [0054]FIG. 14 also illustrates that the fan shaft  164 , which in this case rotates in bearings  166  in a casing  168 , is extended downwardly to a position well beneath the fan  146  and duct  160 . The lower end of the shaft serves as a rotary power take-off and can be used to provide rotary power applications other than air extraction or air supply, such as electrical power generation, grain milling or water pumping.  
         [0055]    A lifting eye  170  is provided at the upper end of the central shaft  172  of the VAWT and auxiliary turbine to facilitate mechanical lifting of the fan assembly.  
         [0056]    Referring to FIG. 17, the fan assembly  100  also includes a handbrake mechanism  174 . This mechanism has a lever  176  pivoted at  178  and carrying a brake pad  180  at one end and a handle  182  at the other end. The handle can be pushed down manually to urge the brake pad  180  upwardly against a plate  182  forming the bottom of the fan impeller thereby to slow down and eventually stop the turbine and fan when maintenance or inspection of the rotary components is necessary. The braking position of the mechanism is illustrated in broken outline.  
         [0057]    The mechanism also includes a spring  184  supported loosely on a pin  186 . When the handbrake is inoperative the spring merely hangs vertically. However when the handbrake is to be held in an applied condition, for instance during maintenance, the spring is swung upwardly and is hooked onto a pin  188  on the handle to hold the handle down.  
         [0058]    Referring again to FIG. 13( b ) there is shown, in broken outline, a modification to the turbine speed governor in which the helical compression spring  136  is replaced by a torsion spring  137  which is wrapped around the pivot axis with it ends hooked around detents  139  on the turbine blade  104  and spoke respectively. The spring  137  holds the turbine blade at an efficient orientation at acceptable turbine speeds but will deflects to allow the blade to pitch negatively in the event of excessive turbine speeds due, for instance, to excessively high wind speeds.  
         [0059]    The invention also envisages another type of governor in which the turbine blade itself incorporates a control surface which will stand proud of the blade surface, at excessively high rotary speeds, to pitch the blade negatively or slow it down.