| 摘要 |
PROBLEM TO BE SOLVED: To reduce beat sound without being accompanied by a decrease in air supply volume of a heat exchanger and suppress cost increase as small as possible by providing a control means for continuously changing rotational speeds of blower fans during operation according to specifications of the blower fans. SOLUTION: Suppose a case in which a control device 2 is interposed in a power circuit of only one blower 5 of two blowers 5, 6 and the other blower 6 is directly connected to a power source. Rotational speed of the blower 5 is continuously changed and rotational speed of the other blower 6 is kept constant. Because the control device 2 continuously changes the rotational speed of the blower 5, cycles of beat become obscure to alleviate the beat. And because air supply volume is changed during operation and air supply volume corresponding to the maximum rotational speed is blown from time to time, a boundary layer formed on a surface of heat exchange section is broken so that an enhanced heat exchange performance is obtained as compared with that obtained by operation at a constant air supply volume. |
