PURPOSE: To control noise to less than a restricted value of surrounding noise in a ventilation fan having a sound sensor by a method wherein a noise restricting value is set in reference to a dark noise around a ventilation fan before its operation and operation of the fan is controlled with the value being applied as a noise upper limit value during operation.
CONSTITUTION: Before starting operation of a ventilation fan 2, a dark noise in an installing environment of a ventilation fan 2 is detected, and then it is inputted to a control part 7. The control part 7 may set a noise restricting value of the ventilation fan in reference to a dark noise. The set noise restricting value is set to the upper limit value to control an operation of the ventilation fan 2 and after a specified period of time elapse, it is stopped. In turn, a surrounding noise is measured and compared with a previous noise value. If there is a variation in the present noise value, the noise restricting value is reset to control an operation of the ventilation fan 2. With this arrangement, it is possible to reduce noise.
NAKAMURA TOSHIO
FURUYA YOSHIAKI
