"His device is a tiny fan which recirculates air out of the cabin rather than pumping stale air around continually." How does just a fan control the recirc/fre

"His device is a tiny fan which recirculates air out of the cabin rather than pumping stale air around continually." How does just a fan control the recirc/fresh air controls for the aircraft as a whole? How is this different from airlines simply choosing a greater fresh-air percentage, at the expense of some fuel?