Method of controlling counter-rotating axial-flow fan

A method of controlling a counter-rotating axial-flow fan, the counter-rotating axial-flow fan comprising:

• a housing including an air channel having a suction port at one end thereof and a discharge port at the other end thereof;
• a first impeller including a plurality of first blades that rotates in the air channel in the vicinity of the suction port;
• a first motor for rotating the first impeller around an axial line;
• a second impeller including a plurality of second blades that rotates in the air channel in the vicinity of the discharge port;
• and
• a second motor for rotating the second impeller counter to the first impeller around the axial line,
• the method controlling the rotational speed of the first motor and that of the second motor such that the temperature of an object to be cooled may be equal to or lower than a given reference temperature, and comprising the steps of:
• starting the first and second motors, which have not been driven, according to a given starting mode;
• subsequently controlling the rotational speed of the first motor and that of the second motor according to a predetermined cooling efficiency mode, which gives priority to cooling the object to be cooled over reducing power consumption of the counter-rotating axial-flow fan, if the temperature of the object to be cooled is higher than the given reference temperature;
• and
• controlling the rotational speed of the first motor and that of the second motor according to a predetermined operating efficiency mode, which maintains the object to be cooled at a temperature equal to or lower than the given reference temperature and reduces the power consumption of the counter-rotating axial-flow fan, if the temperature of the object to be cooled is equal to or lower than the given reference temperature.

A method of controlling a counter-rotating axial-flow fan, the counter-rotating axial-flow fan comprising:

• a housing including an air channel having a suction port at one end thereof and a discharge port at the other end thereof;
• a first impeller including a plurality of first blades that rotates in the air channel in the vicinity of the suction port;
• a first motor for rotating the first impeller around an axial line;
• a second impeller including a plurality of second blades that rotates in the air channel in the vicinity of the discharge port;
• and
• a second motor for rotating the second impeller counter to the first impeller around the axial line,
• the method controlling the rotational speed of the first motor and that of the second motor, and comprising the steps of:
• preparing first basic data by obtaining from data measurements, wherein a counter-rotating axial-flow fan for data measurements is prepared and then flow rate-static pressure characteristics are measured with the ratio of rotational speeds between first and second motors of the counter-rotating axial-flow fan for data measurements being fixed as a certain ratio, and changes in rotational speed of one of the first and second motors of the counter-rotating axial-flow fan for data measurements or changes in total rotational speed of the first and second motors of the counter-rotating axial-flow fan for data measurements as well as changes in motor current value of one of the first and second motors of the counter-rotating axial-flow fan for data measurements or changes in total motor current value of the first and second motors of the counter-rotating axial-flow fan for data measurements are also measured;
• preparing second basic data by obtaining from measurements, wherein a plurality of settings are defined for the ratio of rotational speeds between the first and second motors of the counter-rotating axial-flow fan for data measurements, a flow rate-static pressure characteristic is measured for each ratio of rotational speeds, and a maximum efficiency point is obtained for each ratio of rotational speeds, the second basic data defining a relationship among the measured flow rate-static pressure characteristic, the ratio of rotational speeds, and the maximum efficiency point for each setting;
• obtaining a system impedance curve for a system in which the object to be cooled and the counter-rotating axial-flow fan to be controlled are installed, using the first basic data as well as the rotational speed of one of the first and second motors or the total rotational speed of the first and second motors and the motor current value of one of the first and second motors or the total motor current value of the first and second motors when the first and second motors are rotated with the same ratio of rotational speeds as that used in the data measurements to obtain the first basic data, the system impedance curve being constituted from a quadratic curve passing through a zero point and an operating point of the flow rate-static pressure characteristic;
• comparing the system impedance curve with the second basic data;
• determining as an appropriate ratio of rotational speeds a ratio of rotational speeds at which the maximum efficiency point falls on the system impedance curve or a ratio of rotational speeds at which the system impedance curve approaches closest to the maximum efficiency point;
• and
• fixing the appropriate ratio of rotational speeds thus determined and controlling the rotational speed of the first motor and that of the second motor in a given cooling mode such that the temperature of an object to be cooled may be equal to or lower than a given reference temperature.