Abstract:
An electrically driven fan arrangement, suitable for energy-conserving installations, includes a fan, an electric motor ( 110 ) serving to drive the fan, and associated control apparatus, namely: a sensing apparatus ( 140 ) for sensing a volumetric air flow rate ( 125 ) generated by the fan ( 120 ) and for generating a measured volumetric air flow value (Vmess), and a volumetric flow rate control arrangement ( 160 ) for automatically controlling the volumetric air flow rate ( 125 ) generated by the fan ( 120 ) to a predetermined target volumetric air flow value (V_s). The volumetric flow rate control arrangement ( 160 ) is configured to generate a target rotation speed value (N_s) for the electric motor ( 110 ). A rotation speed controller ( 170 ), which automatically controls the rotation speed of the electric motor ( 110 ) to the target rotation speed rate (N_s) generated by the volumetric flow rate control arrangement ( 160 ), is also provided.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority from German application DE 10 2006 020 421.2, filed 14 Apr. 2006, the entire content of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an arrangement, comprising a fan, adapted for ventilation of an energy-conserving home, office, shop, school, barn, laboratory, or similar structure. 
       BACKGROUND 
       [0003]    Forced ventilation is generally used in energy-conserving buildings, and different volumetric air flow rates are necessary for the ventilation of different rooms, depending on how and when the rooms are used. In a bathroom, for example, a continuous volumetric air flow rate of between 5 liters/second (l/s) and 10 l/s is desirable. When the shower or bath is used, the volumetric air flow rate should then be raised, for example, to 15 l/s, in order to remove excess humidity and to ensure sufficient ventilation of the bathroom. Similarly, in a barn, stable or laboratory, an optimum volumetric flow rate will be higher when the animals are present, and generating methane and humidity, than when the animals are absent. Suitable presence sensors are known in the art and can be used to automatically adjust a target flow rate. Fans having an appropriate power reserve are usually used in this context, to ensure a minimum volumetric air flow rate at different back-pressure values. Such fans, in accordance with their characteristic fan curve, deliver the minimum volumetric air flow rate at a maximum possible back pressure, and a substantially greater volumetric air flow rate at a lower back pressure. If the volumetric air flow rate is too high, however, a great deal of heat is lost, and unnecessary noise occurs, since the fan is always being operated at high speed. 
         [0004]    Volumetric air flow rate regulation systems for radial fans having forward-curved blades are known at present since, with these, an unequivocal relationship exists between the volumetric air flow rate and the torque or motor current. The volumetric air flow rate can thus be suitably regulated as a function of the rotation speed and instantaneous power consumption of the radial fans. 
         [0005]    Because of their mechanical dimensions and 90-degree air deflection, however, radial fans are generally unsuitable for installation or retro-fitting in already-existing ventilation ducts. Arrangements having axial fans, on the other hand, can usually be integrated directly into already-existing ventilation ducts. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to provide an improved fan arrangement for energy-conserving applications, suitable for retro-fitting into older structures as well as newly-built structures. 
         [0007]    According to the present invention, this object is achieved by an arrangement having a fan, in particular having an axial fan, in which a sensing apparatus measures an actual volumetric air flow value, a flow rate control arrangement uses the measured air flow value to generate a target rotation speed value for the fan, and a rotation speed controller automatically regulates the fan speed to match the target rotation speed value. An arrangement of this kind makes it possible to control an electronically commutated motor (ECM), which drives the axial fan, in such a way that the fan generates a substantially constant volumetric air flow rate. To this end, the rotation speed of the ECM is regulated, as a function of a respectively measured volumetric air flow rate of the fan, in such a way that said volumetric flow rate substantially corresponds to a predetermined value. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0008]    Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and depicted in the drawings. In the drawings: 
           [0009]      FIG. 1  is a block diagram of a fan arrangement according to an embodiment; 
           [0010]      FIG. 2  is a perspective depiction of a fan arrangement having a thermal anemometer, according to an embodiment; 
           [0011]      FIG. 3  is a circuit diagram of the thermal anemometer of  FIG. 2 ; 
           [0012]      FIG. 4  is a block diagram of a fan arrangement having a vane anemometer, according to an embodiment; 
           [0013]      FIG. 5  shows a characteristic curve of the vane anemometer of  FIG. 4 ; 
           [0014]      FIG. 6  is a flow chart for an initialization routine of the fan arrangement of  FIG. 2  or of  FIG. 4 ; 
           [0015]      FIG. 7  is a flow chart for a volumetric air flow rate regulating routine during operation of the fan arrangement of  FIG. 2  or  FIG. 4 ; 
           [0016]      FIG. 8  illustrates an example of a characteristic curve of a correction value necessary in the context of  FIG. 6  and  FIG. 7 ; 
           [0017]      FIG. 9  illustrates an example of a measurement protocol of a fan having a volumetric air flow rate regulation system, according to an embodiment; and 
           [0018]      FIG. 10  shows a further example of a measurement protocol of a fan having a volumetric air flow rate control system, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the description that follows, the terms “left,” “right,” “top,” and “bottom” refer to the respective Figure of the drawings, and can vary from one figure to the next as a function of a particular orientation (portrait or landscape) that is selected. Identical, or identically functioning, parts are labeled with the same reference characters in the various figures, and usually are described only once. 
         [0020]      FIG. 1  shows a fan arrangement  100  having a fan  120  that comprises a fan wheel  122 . Associated with fan  120 , in order to drive it, is an ECM  110  controlled by a microcontroller (microprocessor) μC  130 . Microcontroller  130  comprises a temperature and offset compensation arrangement COMP  150 , a volumetric flow rate regulating arrangement V-RGL  160 , and a rotation speed controller N-RGL  170 . 
         [0021]    On the input side, microcontroller  130  is connected to a sensing apparatus FLOW SENSOR  140  for sensing a volumetric air flow rate (indicated schematically with arrows  125 ) generated by fan  120 , and also to ECM  110 . On the output side, microcontroller  130  is connected to ECM  110 . Suitable microcontrollers are available from Microchip, Inc. of Chandler, Ariz. and competing chip vendors. 
         [0022]    It is noted that arrangement  150  is shown, by way of example, as a single component. Its functions can, however, likewise be performed by different components that are implemented separately from one another. 
       Manner of Operation 
       [0023]    When arrangement  100  is in operation, fan  120  is driven by ECM  110  and fan wheel  122  is caused to rotate, and generates an air flow  125  in the direction of sensing apparatus  140 . The flow rate is sensed by sensing apparatus  140 , which generates therefor a measured volumetric flow rate value Vmess. 
         [0024]    Value Vmess is generated using an apparatus suitable for that purpose, for example a thermal anemometer or a vane anemometer. An exemplifying thermal anemometer having semiconductor sensors is described below with reference to  FIG. 3 . An exemplifying vane anemometer having a magnetic sensor is described below with reference to  FIG. 4 . It is noted, however, that the sensing of volumetric air flow rate  125  and the generation of the measured value Vmess can be accomplished in any manner suitable therefor. For example, instead of the anemometers described, any other anemometer—such as a hot wire anemometer, a vane anemometer having a potentiometer, or a windmill anemometer—can be used to measure toe volumetric air flow rate and to generate the measured value Vmess. 
         [0025]    The measured value Vmess and present temperature Tu are applied to temperature and offset compensation arrangement  150 . The latter is configured to correct the measured value Vmess upon startup of fan  120  as a function of the present temperature Tu and, during operation of fan  120 , to compensate for an offset occurring in the measured value Vmess as a result of sensing apparatus  140 . To this end, arrangement  150  comprises a memory unit  152 , in which correction values dependent on the present temperature Tu are stored for correction of the measured value Vmess. Upon startup of fan  120 , arrangement  150  determines from this memory unit  152 , as a function of a respectively ascertained present or instantaneous temperature Tu, a corresponding correction value with which the measured value Vmess is corrected. An exemplifying method for temperature compensation of the measured value Vmess, upon startup of fan  120 , is described below with reference to  FIG. 6 . Examples of correction values are described below with reference to  FIG. 8 . 
         [0026]    During the operation of fan  120 , arrangement  150  ascertains, in the context of a predetermined fan rotation speed, the offset of the measured value Vmess generated by sensing apparatus  140 , and corrects that offset as a function of the present temperature Tu. The corrected offset is stored as a temperature-compensated offset and added to or subtracted from a respective actual measured volumetric flow rate value, by way of an addition or subtraction operation, for offset compensation. An example of a method for offset compensation of the actual measured value during the operation of fan  120  is described with reference to  FIG. 7 , and this will make the concept more clear. 
         [0027]    The temperature- and offset-compensated measured value Vmess, which is referred to hereinafter as Vist, is logically combined with a target volumetric flow rate value V_s and delivered to control arrangement  160 . In this context, for example, a comparison of the two values is made, in order to ascertain a deviation of the value Vist from the target value V_s. As a function of the deviation that is ascertained, arrangement  160  specifies a target rotation speed value N_s for ECM  110 . 
         [0028]    The target rotation speed value N_s is logically combined with the actual rotation speed value Nist and delivered to rotation speed controller  170 . The actual value Nist can be measured or calculated by means of any suitable apparatus for rotation speed sensing, for example utilizing analog or digital rotor position sensors. As regards the logical combination of the two values, by preference a deviation of the actual value Nist from the target value N_s is ascertained. Rotation speed controller  170  uses this deviation to generate a control output S that serves to regulate the rotation speed of ECM  110  to the target rotation speed value N_s generated by volumetric flow rate control arrangement  160 . 
         [0029]    This allows control to be applied to ECM  110  in such a way that fan  120 , regardless of its design, generates a substantially constant volumetric air flow rate. 
         [0030]      FIG. 2  is a partly-section perspective view of an embodiment of fan  120  of  FIG. 1  that is depicted as a so-called tube fan. This has a tube  260  in which the internal stator (not shown) of ECM  110  is arranged in a stator can  270  that is mounted in tube  260  by means of, for example, spokes (not shown). During operation, an external rotor  250  rotates around stator can  270  and therefore around the internal stator; mounted on the periphery of said rotor is fan wheel  122  having fan blades  220  that, during operation, generate volumetric air flow  125  which is transported axially to the left through tube  260 . For this reason, such a fan is called an “axial” fan. The inflow side of fan  120 , having a protective grid  262 , is shown at the right in  FIG. 2 , and the outflow side on the left. 
         [0031]    According to a preferred embodiment, an air-conducting tube  248  is provided at stator can  270 , in which tube at least a part of sensing apparatus  140  is arranged. The latter encompasses in  FIG. 2 , by way of example, a circuit board  245  and two semiconductor sensors  242 ,  244  arranged thereon for sensing volumetric air flow rate  125 , which sensors are part of a thermal anemometer. An example of a thermal anemometer is described below with reference to  FIG. 3 . 
         [0032]    Sensors  242 ,  244  are not thermally coupled, in order to enable a measurement of the flow velocity of volumetric air flow  125  by way of their differential heating. This thermal decoupling can be enhanced by means of corresponding slots in circuit board  245 . The measured volumetric flow rate value Vmess is derived from the flow velocity. 
         [0033]    Provided to the right of the two sensors  242 ,  244  is a temperature sensor  246  that faces toward fan wheel  122  and serves to measure the present temperature Tu. Since any soiling of sensors  242 ,  244  can have a negative effect on the measurement of volumetric air flow rate  125 , and temperature sensor  246  is insensitive to dirt, the latter serves as a dirt catcher for the two sensors  242 ,  244 . 
         [0034]    An enlarged detail view of air-directing tube  248  provided on stator can  270 , with circuit board  245  and sensors  242 ,  244 , and  246  arranged therein, is shown at  280  in a plan view from the left. Because sensors  242 ,  244 , and  246  are arranged in a line behind one another so that temperature sensor  246  can serve as a dirt catcher for semiconductor sensors  242 ,  244 , only semiconductor sensor  242  is visible at  280 . 
         [0035]    Air-conducting tube  248  causes a unidirectional air flow to be directed over sensors  242 ,  244 ,  246 , in order to enable an accurate measurement of volumetric air flow rate  125 . This is necessary because at maximum back pressure, air is no longer delivered through tube  260 , but a highly turbulent air flow can nevertheless occur in the region of air-conducting tube  248  because of the effect of fan wheel  122 . This flow can greatly distort the measurement of the flow velocity and is therefore suppressed by the action of air-conducting tube  248 . 
         [0036]      FIG. 3  is a simplified circuit diagram of an example of a circuit  300  with which a thermal anemometer according to a preferred embodiment can be implemented. Circuit  300  comprises two bipolar transistors  310 ,  320  that serve as semiconductor sensors  242 ,  244  for the measurement of volumetric air flow rate  125  of  FIG. 2 . 
         [0037]    The collector of transistor  310  is connected on the one hand via a resistor  344  to its base, and on the other hand via a lead  342  to a supply voltage source VCC. Its emitter is connected to the collector and base of transistor  320 . Its base is connected via a lead  362  to the output of an operational amplifier  385 , and via two series-connected resistors  364 ,  376  to a load  382  that is connected on the one hand to the non-inverting input of operational amplifier  385  and on the other hand via two series-connected resistors  384 ,  386  to a lead  392 . Power is applied to operational amplifier  385  using supply voltage source VCC and ground GND. The inverting input of operational amplifier  385  is connected via a resistor  378  to the base of transistor  320 , which base is connected to ground GND via a resistor  374 . The emitter of transistor  320  is connected on the one hand to a lead  392  and on the other hand via a resistor  394  to ground GND. 
         [0038]    Load  342  is connected via a capacitor  346  to ground, and also to the collector of an npn transistor  330  whose emitter is connected on the one hand via a capacitor  366  to lead  362 , and on the other hand to the inverting input of operational amplifier  385 . The transistor&#39;s base is connected via a lead  332  to the output of an operational amplifier  395 , which output is also connected, via a resistor  398 , to its inverting input and at which the measured volumetric flow rate value Vmess is generated. The inverting input of operational amplifier  395  is furthermore connected to VCC via a series circuit of two resistors  304 ,  306  arranged in a lead  302 , and to ground GND via a resistor  396 . The non-inverting input of operational amplifier  395  is connected to lead  392 . 
         [0039]    When circuit  300  is in operation, operational amplifier  385  produces, regardless of temperature-induced changes in resistance and changes in ambient temperature, a predetermined substantially constant temperature difference of, for example, 25° C. between the two series-connected transistors  310 ,  320  through which a current IQ flows. Operational amplifier  385  achieves this by maintaining a constant ratio between the base-emitter voltages (U BE ) of transistors  310 ,  320 , the power dissipation of the latter being controlled by influencing current IQ. An approximately square-law ratio exists between IQ and the power consumption of transistors  310 ,  320 . 
         [0040]    Because the two transistors  310 ,  320  carry the same current IQ, their relative energy delivery is determined only by their collector-emitter voltage (U CE ). Circuit  300  is designed so that during operation, the collector-emitter voltage of transistor  310  (U CE1 ) is greater than the collector-emitter voltage of transistor  320  (U CE2 ). Transistor  310  therefore always absorbs more energy regardless of the magnitude of current IQ, and therefore becomes warmer than transistor  320 , which is connected as a diode. When the volumetric air flow rate of fan  120  is then increased, the thermal resistance of transistors  310 ,  320  decreases, and operational amplifier  385  maintains a constant value of the temperature difference by raising current IQ. This current is sensed by resistor  394  and amplified by operational amplifier  395 , at whose output the value Vmess is generated. 
         [0041]    In interaction with transistor  330 , operational amplifier  395  limits the voltage at resistor  394  to a maximum of 2 V. This prevents a blocking that would occur if the output of operational amplifier  385  were to rise to approximately 5 V. In that case, U CE1  would approach U CE2  and it would be impossible to achieve the predetermined temperature difference. Resistors  344 ,  374  similarly prevent blocking when fan  120  is switched on. The square-law ratio existing between IQ and the power consumption of transistors  310 ,  320  makes a good contribution to linearization. 
         [0042]      FIG. 4  is a block diagram of a further preferred embodiment of fan  120  of  FIG. 1  , which is depicted once again in  FIG. 4 , by analogy with  FIG. 2 , as a tube fan having the schematically indicated tube  260 . Components identical, or functioning identically, to ones in  FIGS. 1 and 2  are therefore omitted in FIG.  4 —for example, microprocessor  130  of  FIG. 1  or temperature sensor  248  of FIG.  2 —or are characterized using the same reference characters and are not described again in detail. 
         [0043]      FIG. 4  illustrates one implementation of sensing apparatus  140  of  FIG. 1  utilizing a vane anemometer  410  and a Hall sensor  430  associated therewith. Vane anemometer  410  comprises an air vane  420  that is joined to a torsional spring  422  and comprises at one end a permanent magnet  424  that generates a magnet field at Hall sensor  430 . 
         [0044]    During the operation of fan  120 , air vane  420  is deflected by volumetric air flow rate  125 ; the deflection depends on volumetric air flow  125 , i.e. the greater the volumetric air flow rate  125 , the greater the deflection of vane  420 . Torsional spring  422  counteracts the deflection of vane  420  in order to move it back into its rest position. 
         [0045]    The deflection of vane  420  is sensed with Hall sensor  430 . Because a deflection of vane  420  causes magnet  424  to move away from Hall sensor  430 , as is evident from  FIG. 4 , the field strength of magnet  424  occurring at sensor  430  is a direct indication of the deflection of vane  420 . In order to sense this field strength, an analog Hall IC, for example, is used to implement sensor  430 ; in this, the output voltage or Hall voltage is directly proportional to the field strength. The measured volumetric flow rate value Vmess is derived from this Hall voltage. 
         [0046]    By journaling air vane  420  at its center of gravity, fan  120  can be installed in positionally-independent fashion, i.e. without regard to any particular required orientation. In a particularly advantageous embodiment, magnet  424  is implemented here as a counterweight to the weight of the deflectable blade of vane  420 . 
         [0047]      FIG. 5  shows a measurement diagram  500  that illustrates an exemplifying Hall voltage  530 , measured with vane anemometer  410  of  FIG. 4 , as a function of various deflection angles of air vane  420 . Corresponding deflection angles are plotted, in degrees, on horizontal axis  510 , and Hall voltages measured at the corresponding deflections are plotted on vertical axis  520 . 
         [0048]    It is evident from  FIG. 5  that Hall voltage  530  is maximal when vane  420  is in its rest position, and decreases with increasing deflection. 
         [0049]      FIG. 6  shows an “Init Voffset” routine S 600  that is executed by temperature and offset compensation arrangement  150  of  FIG. 1  at each startup or initialization of fan  120  of  FIG. 1 ,  2 , or  4 , i.e. when fan wheel  122  is at a standstill. Routine S 600  serves to determine a correction value for zero balancing or calibration of fan  120 . 
         [0050]    Because fan  120  is not in operation upon execution of routine S 600 , its fan wheel  122  should be at a standstill and the measured volumetric flow rate value Vmess should thus be zero. As a rule, however, a value Vmess that is not equal to zero can nevertheless occur, as a result of component tolerances, i.e. manufacturing variations. Fan  120  is therefore calibrated by the zero-balancing produced by routine S 600 . 
         [0051]    At S 602 , the ambient temperature is measured by temperature sensor  248  and set as the present temperature Tu. 
         [0052]    At S 604 , a correction value Vtemp associated with the present temperature Tu is determined, for zero balancing of value Vmess, from a table stored in memory unit  152  of arrangement  150 . Examples of correction values as a function of corresponding present temperatures Tu are depicted in  FIG. 8 . 
         [0053]    At S 606  the volumetric flow rate value Vmess is sensed. 
         [0054]    At S 608  a corresponding correction value Voffset (where Voffset :=Vmess−Vtemp) is ascertained for zero-balancing. Routine S 600  then ends at S 609 . 
         [0055]      FIG. 7  shows a “Calc Vist” routine S 700  that is executed during the operation of fan  120  of  FIG. 1 ,  2 , or  4  by temperature and offset compensation arrangement  150  of  FIG. 1 . Routine S 700  serves for temperature and offset compensation of the measured volumetric flow rate value Vmess, which exhibits an error that is dependent on the particular present temperature Tu and, as a rule, rises with increasing temperature Tu. 
         [0056]    Analogously with S 602  and S 604  of  FIG. 6 , at S 702  and S 704  a respective present temperature Tu, and a correction value Vtemp associated therewith, are determined. 
         [0057]    At S 706 , analogously with S 606  of  FIG. 6 , the measured volumetric flow rate value Vmess generated by fan  120  is sensed, although this value is not fault-free because of temperature and offset. A temperature and offset compensation is therefore performed at S 708 . 
         [0058]    As is evident from  FIG. 7 , at S 708  the value Vmess is corrected by the correction value Vtemp determined in S 704  and by the correction value Voffset determined at S 608  of  FIG. 6 , is this case (by way of example) using a subtraction operation. This yields the temperature- and offset-compensated value Vist, where Vist :=Vmess−Voffset−Vtemp. Routine S 700  then ends at S 709 . 
         [0059]    It is noted that routines S 600  of  FIG. 6  and S 700  of  FIG. 7  can also be utilized separately from one another. For example, the calibration of fan  120  could already be accomplished at the factory in the context of production. An execution of routine S 600  upon startup of fan  120  can in this case be omitted, so that only routine S 700  is executed during the operation thereof. 
         [0060]      FIG. 8  is a diagram  800  that illustrates an example of a characteristic curve  830  of the temperature profile of the volumetric air flow rate measurement according to embodiments of the invention. Characteristic curve  830  defines the temperature-dependent correction values Vtemp that are utilized in routines S 600  of  FIG. 6  and S 700  of  FIG. 7 . 
         [0061]    As is apparent from  FIG. 8 , corresponding temperatures in ° C. that represent temperatures Tu are plotted on horizontal axis  810 . Correction values Vtemp associated with said temperatures are plotted on vertical axis  820 . Said values increase, in accordance with characteristic curve  830 , with rising temperature Tu. 
         [0062]      FIG. 9  shows an example of a measurement chart  900  of the volumetric air flow generated by fan  120  of  FIG. 1 , with four different measurement curves  930 ,  940 ,  950 ,  960 . The measured volumetric flow rate value Vmess is plotted on horizontal axis  910 , and measured back-pressure values Δp are plotted on vertical axis  920 . 
         [0063]    Curve  930  was measured during operation of the fan at maximum fan speed without automatic volumetric air flow rate control. This curve illustrates the maximum volumetric air flow rate that can be generated by fan  120  at a specific back pressure, which rate is fan-specific. As curve  930  illustrates, the volumetric air flow rate generated by fan  120  is not constant, but varies in inverse proportion to the back pressure, i.e. the greater the back pressure, the lower the volumeric air flow rate that is generated. 
         [0064]    Curves  940 ,  950 ,  960  illustrate measurements utilizing automatic volumetric air flow rate control as shown in  FIGS. 2 to 4 , each of these curves being based on a different target volumetric flow rare value V_s. As is evident from these curves  940 ,  950 ,  960 , the volumetric air flow rate generated by fan  120  is in each case substantially constant up to a certain back pressure. 
         [0065]      FIG. 10  shows an example of a measurement chart  1000  with four different measurement curves  1030 ,  1040 ,  1050 ,  1060  that illustrate the dependence of the actual rotation speed value Nist of fan  120  (plotted on vertical axis  1020 ) on the back pressure Δp (plotted on horizontal axis  1010 ). These were respectively ascertained in the context of the measurement of curves  930  to  960  of  FIG. 9 . Curve  1030  was accordingly measured in the context of operation of the fan at maximum fan speed without automatic volumetric air flow rats control, as a basis for comparison. 
         [0066]    Curves  1040 ,  1050 ,  1060  illustrate measurements utilizing volumetric air flow rate regulation according to the present invention as shown in  FIGS. 2 to 4 , each of these curves being based on a different target volumetric flow rate value V_s. As is evident from these curves  1040 ,  1050 ,  1060 , fan  120  is operated at an increasing rotation speed as the back pressure rises, in order to keep the volumetric air flow rate generated by said fan substantially constant. 
         [0067]    Numerous variants and modifications are of course possible, within the scope of the inventive concept.