[buffalobillpatrick]

My HRV will pull stale air from 3 bathrooms + Greatroom.
Fresh incoming air will dump into mechanical room -> greatroom, then circulated to rear closets in 3 bedrooms.

4x Panasonic FV-11VQ5 110cfm, high Eff. ceiling ventilation fans.
Each has a timer wall switch for on demand needs.
These provide stale air into HRV.

4x PIR (Human IR motion detection sensors) input to Arduino.

If PIR-1 detects someone, Arduino energizes R-1 for 8hrs. (time adjustable)
During this 8hrs a mechanical timer (adjustable) will turn F-1 on intermittently (say 15min on & 45min off)

This is replicated for: PIR-2, R-2, F-2 : PIR-3, R-3, F-3 : PIR-4, R-4, F-4

This elemonates wasting energy to automatically ventilate any section of house where people haven't been lately. I expect that 2 bedrooms/bathrooms will have very little use except when family comes to visit.

I have this code working on Arduino.

BTW, there is only 1 mechanical timer, it energizes a 4-pole relay so that the 4 exhaust fans are independant of each other.