What about positive extract ventilation, modulating to maintain constant 'suction' while inlets open or close regulated by mechanical humidity sensors? So if internal humidity is low, inlets close and the central extract fan slows down.

Posted By: tonyMy hobby is energy use reduction and this increase represents a 50% increase in energy use regardless of heat recovery or not !!

Nothing about occupancy

The guidance as I understand it is that you must have a design/system that is capable of ventilating at the stated rates. Not that you have to use it at that rate if it is not required at a particular time! Choosing the appropriate rate for the given occupancy is what should be in the user manual, or in automatic sensors (e.g. humidity or CO2 sensors). So I don't think the guidance, which was revised a couple of years ago I think, does represent an increase in energy usage and nor does it ignore occupancy. It simply says that if your entire family comes for Christmas then they shouldn't suffocate or suffer too many brussel sprout smells.

The good bit is that PIV and PSV are no longer allowed

I can't find those terms in the guidance. Where are you looking?

PS An increase of 6 l/s per extra bedroom seems conservativly low. I work on an additional 30 m³/hr (8.33 l/s) per person, rather than room.