Ventilation: Another important component of passive house design is its efficient central ventilation system,
which continually exchanges moist, "polluted" inside air for fresh, filtered outside air to maintain a comfortable,
consistent temperature and humidity level.
Passive houses feature airtight construction to prevent moist room air (or humid outside air, in warmer climates) from penetrating into the home's zone of structural components where it can cause mould, affect inside air quality and even cause structural damage through enabling rot ( and structural damage ) to take place.
The supply of fresh air is not passive as many other systems have it which rely on the wind or temperature gradients to exchange "used" air with fresh. As long as the system is switched on, the air supply is maintained. The rate of air exchange is such that a fan using only modest power levels more or less equivalent to a light bulb, are used.
The vendors of some alternative systems with uncontrolled air movement make much play of the lack of running cost of their systems. In fact, a good forced-air system in a passive house will use less electricity than all (or even just some of) the appliances (such as night-lights, microwave ovens, computers, hi-fi set, etc) that typically are left connected and/or switched on all the time. So that line of reasoning makes no sense, especially compared with the benefits. Remember, a true passive-house design has minimisation of total energy use as a serious, quantifiable goal.
The passive ventilation systems favoured by some component suppliers do not enable efficient conservation of heating energy, since the rate of air exchange is totally dependent on wind or the heat of the sun. In addition, they do not include an filtering system that ensures the cleanliness of incoming air.
Read this article and draw your own conclusions.
A range of filter abilities can be installed, so that for localities with severe PM10 or PM3 air pollution, the fine particles which irritate and damage human lungs can be filtered out by design. The best systems have it so that the filter elements are easily changed when they get clogged, as eventually they will.
This also means, for example, that flies, wasps, bees, hornets, mosquitos, moths and other flying nasties, can not get into the house when the inbuilt ventilation system is the only one being used. Pollen, dust, soot, smoke, and other particulates are also trapped by the filters.
Since fresh air is forced into the house by the fan, and the house is quite air-tight, there has to be provision to let the used air out. This is done by providing air outlets in the places most needing it; moist places such as bathrooms, smelly places such as toilets, parts of the house most distant from the air inlets. This collected air passes through the heat exchanger on its way outside.
The used air passes through a heat exchanger to heat the incoming air; especially important in winter.
New Zealand has a windy climate. There are coastal breezes, sometimes rather strong, and always there is a procession of southerly cold front gales alternating with strong winds and gales from the north-west. Some places, such as the West Coast also have strong easterly winds.
For systems such as the manually adjusted ventilation systems now mandatory under 2011 building laws, and of course "normal" houses with only windows and doors to use for ventilation, it is a constant chore to monitor and adjust openings, and to put "sausages" under doors for draft control, to get reasonable ventilation and temperature control as required for specific wind characteristics and time of day.
With the ventilation systems used in passive houses, such chores become a thing of the past, as the automated system does it all, leaving the occupants merely to adjust the base setting as often as needed.
Where houses rely on open windows for ventilation, these same open windows cause other problems; a change in the weather often brings fast wind gusts and with windows open the gusts blow into rooms breaking ornaments, blowing papers off desks, and so on. They also provide easy entry for burglars.
In areas subject to high fire hazard from vegetation fires, open windows give easy entry for flying embers and sparks to set light to curtains and carpets. The ventilation systems used in passive houses remove these hazards, unless people choose to open windows in hazardous conditions.
All for a running cost equivalent to that of a 50 watt incandescent light-bulb.
Would you like to see a passive house in New Zealand now?
You can follow the blog of the first build at
New Zealand's first Passive house blog-spot
Another NZ passive-house is documented on-line, on facebook. If you are a facebook user, you should have no problems viewing these pages.
A New Zealand Passive house set of informative pages
A New Zealand Passive house - the base page
Congratulations to Brooke the Architect (MOAA Architects) for what looks like a thorough job, and likewise the builder for following instructions so well. Lots of construction detail in here.
Links to pages about the seven precepts of Passive House design.
Very efficient Insulation
No thermal bridges
Passive solar gain
Prices / costs