As a way to experiment and start prototyping physically responsive spatial elements, I developed a simple "windwall" incorporating a passive infra-red (PIR) sensor, an actuated switch, and a number of ordinary house fans controlled by an arduino microcontroller.
As was evidenced by my class demo, the arrangement of the motion sensor to the zone of activity caused the relay to be consistently triggered. I programmed the sensor with 30 seconds of calibration time to create a baseline with a relatively high amount of motion, but it was ineffective at creating the response I wanted. Repositioning the sensor, creating a smaller view cone for the fresnel lens, or using a PIR with a manually controlled sensitivity would have made the interaction more satisfactory.
One very helpful tool was the PowerStripTail, available here for less than $20. It is essentially an independently powered relay that allows for the conversion of electricity between the 5v microcontroller and up to 120v AC. I powered three house fans on an ordinary powerstrip plugged into the PowerStripTail. This greatly reduced the time and circuitry required for this experiment.