Apparatus and method for maintaining an operating condition for a blower
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.