Apparatus and method for maintaining an operating condition for a blower

Abstract

An apparatus and method for maintaining a predetermined flow rate in a ventilation system having a motor driven blower. In one embodiment, the blower is a draft inducer. The apparatus contains a module for determining the impedance at the outlet of the blower. The impedance results from the length of pipe through which the blower blows the exhaust from a heating device, such as a hot water heater along with any obstructions. The impedance is determined by using a look-up table to compare the measured rotation rate (RPMs) of the motor shaft to values in the look-up table. The RPMs are measured by a sensor that is coupled to the rotating shaft of the motor. The sensor provides a sensor signal to the impedance module. Once a substantially matching value is found, the corresponding impedance is obtained from the look-up table. The impedance is then passed to a module for setting the motor speed. The motor speed module adjusts the speed of the motor based on the impedance to maintain a constant flow rate.

1 . An apparatus for maintaining a predetermined flow rate in a ventilation system having a motor driven blower, the apparatus comprising: 
 a module for determining an impedance at the output of the blower;    a module for setting the motor to a speed that will maintain the predetermined flow rate, wherein the speed is determined based upon the impedance.    
   
   
       2 . The apparatus according to  claim 1  wherein the blower is part of a draft inducer.  
   
   
       3 . The apparatus according to  claim 2  wherein the input of the blower is coupled to an outlet of a hot water heater.  
   
   
       4 . The apparatus according to  claim 1  wherein in the module for determining, the module determines an impedance that is equivalent to a length of pipe attached to the output of the blower.  
   
   
       5 . The apparatus according to  claim 1  wherein the module for determining and the module for setting both use a processor  
   
   
       6 . The apparatus according to  claim 5  wherein the processor is shared  
   
   
       7 . The apparatus according to  claim 1  wherein the apparatus includes a sensor for sensing rotation of a shaft of the motor  
   
   
       8 . The apparatus according to  claim 1  wherein the module for setting the motor accesses a look-up table having a set of values to determine a speed for the motor based upon the impedance.  
   
   
       9 . A method for maintaining a flow rate at an outlet to a blower having a motor, the method comprising: 
 measuring the rate of rotation of the motor; and    adjusting the motor until the measured rate of rotation substantially matches an empirically determined rate.    
   
   
       10 . The method according to  claim 9 , wherein adjusting the motor includes changing a duty cycle of a pulse width modulated waveform.  
   
   
       11 . The method according to  claim 9 , further comprising determining an impedance coupled to the outlet of the blower by comparing the measured rotation rate to empirically determined rates in a look-up table wherein the look-up table has an association between an empirically determined rate and an impedance.  
   
   
       12 . The method according to  claim 9  further comprising: 
 selecting the empirical rate wherein the empirical rate produces a flow rate producing substantially optimal energy efficiency of a hot water heater, wherein the hot water heater is coupled to the inlet of the blower.    
   
   
       13 . The method according to  claim 12 , further comprising determining an impedance coupled to the outlet of the blower using a look-up table that associates each empirically determined rotational rate with an impedance by comparing the measured rate of rotation to the empirically determined rates within the look-up table.  
   
   
       14 . The method according to  claim 11  wherein the rate of rotation of the motor produces a flow rate that removes a substantially minimal amount of heat from a heating device coupled to the blower.  
   
   
       15 . The method according to  claim 14 , wherein the heating device is a hot water heater.  
   
   
       16 . A method for producing a near optimal energy efficient flow rate using a blower powered by a motor between a heat producing source and an outside environment, the method comprising: 
 setting a duty cycle for a DC motor to a preset level using a processor;    sampling the revolution rate of the DC motor;    comparing the sampled revolution rate to a value in a look-up table;    if the sampled revolution rate is not within a predetermined range of the value in the look-up table, varying the duty cycle of the DC motor until the sampled revolution rate matches the value in the look-up table.    
   
   
       17 . The method according to  claim 16 , further comprising: 
 determining an impedance at the outlet of the blower.    
   
   
       18 . The method according to  claim 17 , wherein determining an impedance includes obtaining a look-up table from memory containing associations between duty cycle, revolution rate and impedance; and 
 selecting an entry within the look-up table having the closest revolution rate to the sampled revolution rate.    
   
   
       19 . The method according to  claim 16 , wherein the predetermined range is zero and therefore requires an exact match.  
   
   
       20 . The method according to  claim 16 , further comprising: 
 providing to a processor a diameter of an exhaust pipe to be used with the blower.    
   
   
       21 . The method according to  claim 16  wherein the blower is a draft inducer.  
   
   
       22 . The method according to  claim 21 , wherein the draft inducer is coupled on a first side to a hot water heater and on a second side to the impedance.  
   
   
       23 . The method according to  claim 22  wherein the impedance is a length of pipe.  
   
   
       24 . A system producing a near optimal energy efficient flow rate at an outlet of a blower, the system comprising: 
 a processor producing a pulse width modulated signal having a duty cycle;    a DC motor having a shaft and receiving the pulse width modulated signal causing the shaft to rotate;    a blower coupled to the DC motor    a rotation sensor sensing the rotations and outputting a signal representative of the rotations;    wherein the processor receives the output signal from the rotation sensor, determines the number of revolutions per a time period that the shaft rotates, and adjusts the pulse width modulated signal until the number of revolutions per time period reaches an empirically determined value.    
   
   
       25 . The system according to  claim 24 , wherein the empirically determined value is associated with an impedance.  
   
   
       26 . The system according to  claim 25 , wherein the processor determines the impedance at the outlet by determining the revolutions per time period and compares the determined revolutions to a look-up table containing an association between revolutions per time period and impedance.  
   
   
       27 . The system according to  claim 26  wherein the processor accesses a look-up table and based upon the impedance determines the empirically determined value.