On 17 and 18 April, 100 speakers from around the world will convene at the 13th International Passive House Conference in Frankfurt/Germany, to present and discuss new trends, products and developments around passive housing. The conference will examine implementation of the Passive House concept in places like Korea, USA, Spain, Slovakia and many Scandinavian countries. As always, there is an accompanying exhibition, showcasing the latest in Passive Housed technology. See www passivhaustagung.de for more.

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For inexplicable reasons a doctrine of preferring “natural” ventilation prevails in NZ. Funny though, hardly anyone advocates “natural” laundry practices – for good reasons: a (washing) machine can do the job more efficiently, conveniently and environmentally friendly. Same goes for ventilation. “Naturally” ventilated buildings are usually either under- or over ventilated; additionally, there is no way to re-use the warmth of the outgoing air. As natural ventilation relies on weather and stack effects, it is impossible to control airways or amounts of air exchanged. Much like throwing your laundry in the river, and picking it up 2-3 km downstream, hoping that nature has sufficiently tumbled and spun the load.
Please note: mechanical heat recovery ventilation is not air conditioning; air is always fresh - not reused; you can open windows and doors as you please; fine tune to your hearts content; switch the system on and off as you wish. It is – unlike most mechanical ventilation systems on the market in NZ - a balanced system, meaning: there is no pressure differential between indoors and outdoors. A well designed system is silent, too, and can filter pollutants, allergens, and noise.
Yes, mechanical ventilation uses energy - but efficient systems need very little electrical energy to do a good job - plus true heat recovery models regain thermal energy from outgoing air, thus saving energy for heating the fresh air.
In cars, it is long understood that a mechanical ventilation system gives far better control of the in-car environment, than just relying on opening windows. In fact, I sometimes jump to the conclusion that New Zealanders are spending that much time in their cars, because there – unlike in their homes – they are able to maintain comfortable climate conditions. In a Passive House with mechanical heat recovery ventilation the comforts of home can truly be experienced; if this leads to a reduced recourse to the car – the better!

In Auckland, you probably would not have wanted to live in a house that relies solely on solar gains to be warm in recent weeks, because sunshine hours were rather rare. I take this as an occasion to make a distinction between Passive Solar schemes and Passive Houses:

Passive Solar	Passive House
Specific insolation requirements	Works with minimal solar gains (e.g. southern orientation)
Additional thermal mass requirements	Does not need additional thermal mass
Needs favourable weather conditions to be comfortable	Is comfortable year round
Provides solar gains predominantly during spring and fall	No heating requirements during spring and fall
Relies on natural forces for ventilation	Uses controlled mechanical ventilation
Design principles are widely promoted	Clearly defined and proven concept

Achieving a good indoor-outdoor flow is generally desirable for a residential building. Yet, when indoors and outdoors are not sufficiently separated, it is impossible to condition the indoors efficiently. You need a lot of energy to keep the interior of a sieve in a thermal state different from its environment.
There most definitely has to be an air exchange between inside and outside, and this really is a matter of survival. However: it is nearly impossible to construct a house with involuntary openings, i.e. air gaps in just the right way to provide optimum ventilation regardless of outdoor conditions. Thus, while they are not airtight, average houses are usually not at all well ventilated. Humidity and insufficient oxygen supply are a result. And this is where the circle closes: a precondition for efficient ventilation is reliable airtightness of the building envelope. Without it, airways and ventilation effects are uncontrollable.
Nothing prevents you from opening windows and doors in an airtight building. It’s just: only in an airtight building can you use windows and doors – or an efficient heat recovery ventilation system, to control in- and exfiltration. The added bonus is that noise and six legged friends will be bared from entering as well – unless you open a door or window for them!