The author makes a point at the end alluding to a violation of the conservation of energy, By, to be fair, Dyson only says that this fan multiplies to amount of

The author makes a point at the end alluding to a violation of the conservation of energy, By, to be fair, Dyson only says that this fan multiplies to amount of air, not the amount of energy. All fans multiply the air moved (simply by dragging adjacent air along for the ride), so I'm not sure why this claim should be a concern.