Questions about Ventilation

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Can I avoid using the Mechanical Heat Recovery Ventilation System?


No.  There is no point in building a Passive House without this for recovery of heat loss from ventilation. A Passive House uses mechanical ventilation with a heat recovery system which retains 85% of the heat from extracted stale air. If you decide not to install such a system then you will have to install a conventional heating system (such as underfloor heating or radiators) incurring costs which would pay for the mechanical heat recovery ventilation system in the first place. 
It is important to note that it is well proven that ventilation systems are extremely efficient, providing a controlled ventilation rate throughout the house and ensure clean, fresh air is delivered through the use of filters in the system.

Is it unhealthy to live in an airtight house such as a Passive House?


No, because the house provides an abundance of fresh air using the ventilation system. This is a high air quality standard. Typically fresh air arrives into a conventional house via means of ‘hole in the wall’ vents/drafts/open windows. These are somewhat uncontrolled unlike Passive Houses which have on average 8-12 air changes per day. The fine filters in the ventilating system keep out dirt and pollen which reduces allergies and asthmatic conditions.

Are there problems with bacteria, noise and drafts with the ventilation system?


The ventilation system in a Passive House is a fresh air supply system, not an air conditioning system that re-circulates inside air (this is where bacteria growth is a problem in re-circulating systems). This fresh air is also filtered as it enters into the system.
Fan and valve noises in the Passive system are almost completely eliminated by sound control measures such as vibration isolation mounts, low air speed and acoustic lining in the ducts. 
Jet nozzles guide incoming air along the ceiling from where it is uniformly diffused throughout the room at low velocities that are barely perceptible therefore no drafts are evident.