The Mechanical Ventilation and Heat Recovery unit is a vital part of a passivhaus. With an airtight house you need a way for fresh air to get in, whilst at the same time not loosing the heat in the house. Ours is a Paul Novus 300 which sits in the coat cupboard by the front door. 
Warm moist air will be extracted from the bathroom, shower room and the kitchen. This enters the unit via one of the silver pipes, warms up the incoming air and the goes to the outside world via one of the black pipes. Meanwhile fresh air is brought in through the other black pipe and after being warmed goes out through the other silver pipe around the house.
So there is a lot of ducting as each room has either an extraction or supply vent.
Upstairs the ducts come up through the airing cupboard and then into the two bedrooms. If you look closely to the left of the window where there is an upright post you can see the extraction vent for the bathroom. Looks rather like a periscope at the present