fan noise versus speed

[Rerouter]

You can define a limit, at what duty cycle does the cost savings reverse, that would be a solid counter argument followup I would think. e.g. at 0.1% bang-bang, how does it compare when you look at similar energy consumption vs the equivalent PWM, If you really wanted to stick the point you could even graph the net gain in airflow vs power consumption with duty cycle control vs bang-bang, as that spin up energy is lost every time in bang-bang

[Simon]

Yea, a brushless speed controllable fan is already cheaper in volume than a brushed one when you consider the per hour cost (40'000 hours versus 10'000) so the controller costs under £100, so any speed regulation will save money but yes your idea is good I may do that.