Method of constant airflow control for a ventilation system
View Patent ↗A method of constant airflow control includes various controls to accomplish a substantially constant airflow rate over a significant change of the static pressure in a ventilation duct. One control is a constant I·RPM control, which is primarily used in a low static pressure range. Another control is a constant RPM control, which is primarily used in a high static pressure range. These controls requires neither a static pressure sensor nor an airflow rate sensor to accomplish substantially constant airflow rate while static pressure changes. Also, the method improves the accuracy of the control by correcting certain deviations that are caused by the motor's current—RPM characteristics. To compensate the deviation, the method adopts a test operation in a minimum static pressure condition. Also disclosed is an apparatus for conducting these control methods.
1. A method of operating an electric motor in a ventilation system, the method comprising:
providing a first target value and a second target value;
detecting an electric current applied to the motor;
detecting a rotational speed of the motor;
computing a value of the product by multiplying the detected current and the detected speed;
determining whether the detected electric current is greater or smaller than a reference value;
when determined that the detected electric current is greater than the reference value, controlling the motor's operation to adjust the computed product value toward the first target value; and
when determined that the detected electric current is smaller than the reference value, controlling the motor's operation to adjust the rotational speed toward the second target value,
wherein controlling the motor's operation comprises transitioning between adjusting the computed product and adjusting the detected rotational speed of the motor in response to the change between a first state, in which the detected electric current is greater than the reference value, and a second state, in which the detected electric current is smaller than the reference value.
2. The method of claim 1 , wherein the motor is coupled with a fan, which blows air in a ventilation duct, wherein controlling the motor's operation generates an airflow with a substantially constant airflow rate in the ventilation duct in a range of a static pressure within the duct.
3. The method of claim 2 , wherein the system does not comprise an airflow rate sensor for detecting an airflow rate generated by the blower, wherein controlling the motor's operation does not use an input of an airflow rate change.
4. The method of claim 2 , wherein controlling the motor's operation generates the substantially constant airflow rate while the static pressure significantly changes.
5. The method of claim 4 , wherein the system does not comprise a static pressure sensor for detecting the static pressure within the duct, wherein controlling the motor's operation does not use an input of a static pressure change.
6. The method of claim 1 , wherein controlling the motor's operation comprises adjusting a turn-on period of the motor so as to maintain the computed value within proximity of the first target value.
7. The method of claim 1 , wherein the first target value is computed using a rated electric current and a rated rotational speed of the motor.
8. The method of claim 1 , wherein the first target value is a fractional value of the product of a rated electric current and a rated rotational speed of the motor.
9. The method of claim 1 , further comprising:
receiving a user input of a desired level of airflow rate; and
obtaining the first target value that corresponds to the desired level.
10. The method of claim 9 , wherein receiving the user input comprises receiving a user's selection among a plurality of predetermined levels, and wherein obtaining the first target value comprises retrieving the first target value from a plurality of values stored in a memory, wherein the retrieved first target value is associated with the user's selection.
11. The method of claim 9 , wherein receiving the user input comprises receiving a user's desired level represented in a number, and wherein obtaining the first target value comprises computing the first target value using the number and a preprogrammed formula.
12. The method of claim 1 , wherein controlling the motor's operation comprises transitioning from adjusting the computed product to adjusting the detected rotational speed of the motor.
13. The method of claim 1 , wherein controlling the motor's operation comprises transitioning to adjusting the computed product from adjusting the detected rotational speed of the motor.
14. The method of claim 1 ,
wherein when the electric current transitions from greater than the reference value to smaller than the reference value, controlling the motor's operation comprises transitioning from adjusting the computed product to adjusting the detected rotational speed of the motor.
15. A method of operating an electric motor in a ventilation system, the method comprising:
providing a blower comprising a motor and a fan coupled to the motor, the blower being configured to generate an airflow in a ventilation duct;
providing a first target value and a second target value;
detecting an electric current applied to the motor;
detecting a rotational speed of the motor;
computing a value of the product of the detected electric current and the detected speed;
determining whether the detected electric current is greater or smaller than a reference value; and
controlling the motor's operation, which comprises:
when determined that the detected electric current is greater than the reference value, adjusting the electric current applied to the motor so as to move the computed product value toward the first target value; and
when determined that the electric current is smaller than the reference value, adjusting the electric current so as to move the rotational speed toward the second target value,
wherein controlling the motor's operation comprises transitioning between moving the computed product and moving the detected rotational speed of the motor in response to the change between a first state, in which the detected electric current is greater than the reference value, and a second state, in which the detected electric current is smaller than the reference value.
16. The method of claim 15 , wherein the system does not comprise a static pressure sensor for detecting a static pressure within the duct.
17. The method of claim 15 , wherein the system does not comprise an airflow rate sensor for detecting an airflow rate generated by the blower, wherein controlling the motor's operation does not use an input of an airflow rate generated by the blower.
18. The method of claim 15 , further comprising:
determining that the detected electric current changes from a value greater than the reference value to a value smaller than the reference value; and
transitioning controlling the motor's operation from moving the computed product value to moving the rotational speed.
19. The method of claim 15 , wherein when the detected electric current is greater than the reference value, adjusting the electric current is to maintain the computed product value within proximity of the first target value.
20. The method of claim 15 , wherein when the detected electric current is smaller than the reference value, adjusting the electric current is to maintain the rotational speed within proximity of the second target value.