Abstract:
An apparatus for controlling an air distribution system for maintaining a rate of air flow in the system at substantially the target air flow rate, wherein the apparatus comprises: 
     means for detecting current speed and torque of said motor and generating said current speed signal and torque signal after detection;
 
means for receiving current speed signal and torque signal and calculating current air flow rate in the air distribution system wherein the calculated current air flow rate is being compared to the target speed signal of the air flow rate and the current air flow rate is adjusted according to the target speed signal of the air flow by generating a control signal; and
 
means for controlling the motor speed in response to the control signal for maintaining the rate of air flow in the system at substantially the target speed signal of the airflow rate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to systems for conditioning air and specifically to control a system for maintaining a desired flow rate of conditioned air through at least part of the system regardless of the static pressure therein. 
       BACKGROUND ART 
       [0002]    Various different techniques have been used in an attempt to flow air through a contained space of a system including air distribution systems for conditioning the temperature of the air and the rate of such air flow being in related to the static pressure in the system. The rate of airflow through the air distribution systems also affected by the speed and torque of a motor used in the system. 
         [0003]    One approach involves the laborious task of matching the motor speed and torque with the proper fan to approximate the desired air flow rate for a particular contained space and static pressure of a particular air distribution system. However, this does not accommodate variations in the static pressure in the air distribution system caused by alterations in the system such as the opening, closing or adjusting of a damper connecting a conditioned space in air flow relation with the system. In addition, other devices, such as filter and heat exchangers, may alter the static pressure within the duct system. 
         [0004]    If the fan or blower utilised in such systems is of the fan or blade type, an increase in the static pressure acting on such fan will result in a decrease in the air flow rate. 
         [0005]    Another approach has been to compensate for the alteration in the speed of fans and the electric motors by employing an apparatus for controlling the motor speed, which requires the calculation of constants specific for each apparatus and air distribution system combination. This apparatus includes a controller, which drives the motor at various speeds but cannot be used with a general motor controller. 
         [0006]    It is an object of the present invention to provide an improved system for conditioning air and for maintaining a preselected air flow rate of the conditioned air through at least part of the system regardless of the static pressure therein. 
       SUMMARY OF THE INVENTION 
       [0007]    An apparatus for controlling an air distribution system for maintaining a rate of air flow in the system at substantially the target air flow rate, wherein the apparatus comprises:
       means for detecting current speed and torque of said motor and generating said current speed signal and torque signal after detection;   means for receiving current speed signal and torque signal and calculating current air flow rate in the air distribution system wherein the calculated current air flow rate is being compared to the target speed signal of the air flow rate and the current air flow rate is adjusted according to the target speed signal of the air flow by generating a control signal; and   means for controlling the motor speed in response to the control signal for maintaining the rate of air flow in the system at substantially the target speed signal of the airflow rate.       
 
         [0011]    An apparatus for controlling an air distribution system for maintaining a rate of air flow in the system at substantially the target air flow rate, wherein the microprocessor operates accordance with the following algorithm: 
         [0000]        Qa=A+B*Ta+C/Ta +( D+E*Ta+F/Ta )* Na +( G+H*Qa+I/Qa )/ Na,    
         [0000]    wherein Qa is the actual air flow rate signal, Ta is the present value of the motor speed signal, Na is the present value of the torque signal, and A to I are constants representing characteristics of the blower, motor and variable speed motor controller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a block diagram of an apparatus for controlling air distribution system in one embodiment of the present invention. 
           [0013]      FIG. 2  illustrates a flow diagram of the algorithm of one embodiment of the present invention. 
           [0014]      FIGS. 3  ( a ) and  3 ( b ) illustrate a comparison airflow rate between actual airflow rate and calculated airflow rate. 
           [0015]      FIG. 4  illustrates a performance graph showing revolution versus airflow rate at different external static pressure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  is a block diagram illustrative of an apparatus for controlling air distribution system  10  of one embodiment of the present invention. The apparatus for controlling air distribution system  10  comprises a duct system  15 , a blower  20 , a motor  25 , a variable speed motor controller  30 , an air flow control module  35 , and a system control  40 . The duct system  15  is a conduit used for distributing air to the desired zone. For instance, the duct system  15  may be installed in a building for providing conditioned air to desired rooms therein. As mentioned earlier, static pressures formed within the duct system  15  are affected by dampers  45 , filter  50 , and heat exchangers  55  which are incorporated in the duct system  15 . 
         [0017]    The blower  20  is a device, such as a fan, for causing air to flow in the duct system  15  and is typically installed therein. In one preferred embodiment, the blower  20  comprises a forward curved centrifugal fan. However, the blower  20  may be any type of blade, fan, or other device for moving air in an air distribution system. 
         [0018]    The motor  25  is a device for providing the necessary mechanical power for driving the blower  20 . In one preferred embodiment, the motor  25  includes a stationary assembly  60  with a plurality of winding stages for carrying motor current and further includes a rotational assembly  65  in driving relationship with the blower  20 . The motor  25  may be any device capable of driving the blower  20  such as a brushless DC motor. The motor  25  is drivingly connected to the blower  20  by pulley system  70 . Alternatively, the motor  25  and the blower  20  may be an integrated device such that the motor  25  is inserted into the blower  20 , attached with a set screw and electrically connected therein (not shown). 
         [0019]    The variable speed motor controller  30  is a means for controlling the motor speed in response to a target speed signal  80  generated by the air flow control module  35 , a means for providing a speed signal  85  representative of the speed of the motor  25  and a means for providing a torque signal  90  relatively representative of the torque of the motor. The speed signal  85  may be provided by a device to count pulse sent from the brushless DC motor. The torque signal  90  may be provided by either a device to represent a voltage to be supplied to the motor  25  or a device to represent a current to be supplied to the motor  25 . The variable speed motor controller  30  is a type of armature-voltage control, is responsive to a target speed signal  80  and control a speed of the motor  25  by comparison between a target speed signal  80  and a speed signal  85 . 
         [0020]    The variable speed motor controller  30  is electrically connected to the airflow control module  35  for receiving the target speed signal  80  and for sending the speed signal  85  and the torque signal  90 . The variable speed motor controller  30  is also electrically connected to the motor  25  for applying a voltage to one or more of the winding stages at a time and for commutating the winding stages in a pre-selected sequence to rotate the rotational assembly  65 . Accordingly, the variable speed motor controller  30  controls the speed of the motor  25  in response to the target speed signal  80  provided by the air flow control module  35 . 
         [0021]    The air flow control module  35  is a means for providing a target speed signal  80  in response to a target air flow rate signal  95 , a speed signal  85  and a torque signal  90  as will be explained hereinbelow. The target air flow rate signal  95  is generated by the system control  40 . The speed signal  85  and the torque signal  90  are generated by the variable speed motor controller  30 . The air flow control module  35  comprises a microprocessor  100  for calculating an air flow rate signal  105  by the speed signal  85  and the torque signal  90  and for calculating the target speed signal  80  by the target air flow rate signal  95 , a speed signal  85  and the air flow rate signal  105 . 
         [0022]    The system control  40  is a device or system which supplies the air flow control  35  with a target flow rate signal  95  representative of desired air flow rate. The system control  40  may be responsive to sensors and user input (not shown). 
         [0023]    In one preferred embodiment according to the invention, the air flow control module  35  operates in accordance with a constant airflow algorithm for controlling and compensating the motor speed. This algorithm allows the motor  25  to provide a constant airflow within the air distribution system  10  regardless of variations in static pressure. Controlling the motor  25  in this manner provides enhanced independence of the airflow rate to the static pressure within the air distribution system  10 . The constant airflow algorithm demonstrates the cooperation of the present invention and is described hereinbelow. 
         [0024]      FIG. 2  is a flow diagram of the constant airflow algorithm embodied in the present invention. Beginning at block  120  labelled “start” the first step performed  125  is to send an initial target speed signal which can be selected at any speed signal or may be a final target speed signal at the last operation. In step  130 , the air flow control module  35  receives the target airflow rate signal  95  (“Qt”) transmitted from the system control  140 . In step  135 , the air flow control module  35  receives the speed signal  85  (“Na−1”) transmitted from the variable speed motor controller  30 . In next step  140 , the air flow control module  35  waits for 1 second and after 1 second in step  145 , the microprocessor  100  receives the speed signal  85  (“Na”) transmitted from the variable speed motor controller  30 . In step  150  the microprocessor  100  compares “Na−1” with “Na”. If difference between “Na−1” and “Na” is more than 10 rpm, the microprocessor  100  returns to step  135  to wait for stability of the motor speed. If difference between “Na−1” and “Na” is equal or less than 10 rpm, the microprocessor  100  moves to step  155  to receive the torque signal  90  (“Ta”) transmitted from the variable speed motor controller  30 . In step  160 , the microprocessor  100  calculates an air flow rate signal (“Qa”) by the torque signal  90  (“Ta”) and the speed signal  85  (“Na”) using the following algorithm 
         [0000]        Qa=A+B*Ta+C/Ta +( D+E*Ta+F/Ta )* Na +( G+H*Qa+I/Qa )/ Na,    
         [0000]    wherein Qa is the actual air flow rate signal, Ta is the present value of the motor speed signal  85 , Na is the present value of the torque signal  90 , and A to I are constants representing characteristics of the blower  20 , the motor  25  and the variable speed motor controller  30 . In step  165 , the microprocessor  100  calculates a target speed signal  80  (“Nt”) by the target air flow rate signal  95  (“Qt”), the actual air flow rate signal (“Qa”) and the speed signal  85  (“Na”) using the following algorithm: Nt=Qt/Qa*Na, wherein Nt is a new target speed signal, Qa is the actual air flow rate signal calculated in step  160 , Qt is the present value of the target air flow rate signal  95  and Na is the present value of the speed signal  90 . After step  165 , the microprocessor  100  returns to step  125  to send the new target speed signal (“Nt”) to the variable speed motor controller  30  and start the cycle again. 
         [0025]      FIG. 3  is a comparison of airflow rate between actual airflow rate and calculated airflow rate by one preferred embodiment of the present invention. The left 4 columns of table A represent test data and the right 2 columns represent calculated results by equation mentioned in step  160  and the constants which are shown in table B on  FIG. 3 . The first column represents the experimental value of the motor speed. The second column represents the experimental value of the static pressure. The third column represents the experimental value of the airflow rate. The forth column represents the experimental value of the torque signal  90 . The fifth column represents the calculated value of the air flow given a particular blower geometry, motor  25 , and variable speed motor controller  30 . The sixth column represents the percent error of the calculated values of the airflow and the experimental values of the airflow. As this chart illustrates, the value of the percent error between the calculated values of the air flow and the experimental values of the air flow are less than 2% and the calculated values of the air flow in one preferred embodiment of the present invention expresses the experimental values of the air flow accurately. 
         [0026]      FIG. 4  is a performance chart of one preferred embodiment of the present invention. On this chart, a horizontal level is an air flow rate with unit CFM, a vertical level is a motor speed and plotted points represent the experimental result in each case that damper  45  open in due order. As this chart illustrates, data of same opening ratio of damper  45  approximate straight line, these straight lines converge to the origin and therefore the calculating algorithm of the new target speed in one preferred embodiment of the present invention is effective. 
         [0027]    Thus, the present invention provides an improved system and method for conditioning air and for maintaining a pre-selected air flow rate of the conditioned air through at least part of the system regardless of the static pressure therein for use in conjunction with numerous duct systems without the need for calibration particular to the specific duct system. 
         [0028]    Although the motor  25  and the variable speed motor controller  30  has been described as a DC brushless motor and a type of an armature-voltage control, one skilled in the art will readily recognise that a combination of an induction motor and a type of a primary voltage control or combination of an induction motor and a type of a primary frequency control may also control the speed of the motor  25 . 
         [0029]    Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that various other change, omissions and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.