Abstract: Disclosed is wind flow operated ventilation and energy harnessing device, comprising an L-shaped flow pipe (101/201) with one arm sweeping horizontally while the other rotatable on a stationary vertical pipe (102/202) connected with the space being ventilated. The open end of the horizontal portion is flared into collar (106) or bell-shaped mouth (206) forming evacuating or pressurizing flow pipe respectively. The direction changers (108/208) are used to maintain the back of collar (107) of flared portion (106) or open end (207) of bell-shaped mouth (206) facing upstream wind. The wind on striking the back of collar (107) or the open end (207) of bell-shaped mouth (206) creates evacuation or pressurization effect respectively for ventilation. A wind turbine fitted inside stationary vertical pipe harnesses energy.