The build

The black wrapping threw me. P is all excited and keen to hear all about it.

For P
So the mvhr is a ventilation system. The house is well sealed so we need to ventilate it, on less sealed houses this would be done with trickle vents above the windows. 
So the idea is to pump air in from outside at a certain rate (from memory it's about 0.5 air changes/hour)
So rather than filling the house with cold air an mvhr takes warm, wet air from areas like the kitchen and bathroom and passes this air through a heat exchanger thus warming the cold, dry outside air and recovering the heating which would potentially be lost.
In theory this unit will pay for itself eventually but I think the time period is really very high ??