Passive housing

Passive housing

1. Description

Passive housing is not any particular type of construction, but a construction standard that meets certain criteria.

It is a building that reaches a comfortable ambient temperature without any conventional heating in winter and without air-conditioning in summer.

Studies on this type of construction began in Germany in the 1980s. Those studies were based on the development of low-energy houses in Sweden and Denmark, where they were already a construction norm at that time. The first passive houses were built in 1991 in Germany, where there are now several thousand of them.

The term "passive" means that, even if special techniques are required, it is primarily the ambient energies (heat from the sun through window glazing) and internal sources of heat (appliances and occupants), which enable the interior of the building to be kept at a comfortable temperature throughout the year.

2. Certification

"Passive House" certification is granted by the "Plateforme Maison Passive" (Passive House Platform). To receive this certification, the housing must meet the following criteria :

Primary energy needs, which represent the non-renewable (fossil) energy actually consumed, are calculated by applying coefficients to all of the energy used, in so far as some of the energy consumed involves a more significant use of primary energy (e.g. non-renewable electricity), and the rest, less (all renewable energies: wind, solar, biomass).
Draught-proofing means that a passive house is on average 10 times more 'airtight' than an ordinary house, which substantially reduces the heating needs.
The increase in performance between the different construction standards can be seen below :

source : Passiefhuis Platform

Certification is only granted if the building meets a series of technical standards, partially validated by the blower door test or infiltrometry, which consists of detecting, visualizing and measuring draughts, which enter through the shell of the building. The measuring technique consists of creating a slight vacuum within the rooms using a blower door (door with an extractor fan) and detecting those places where air, drawn in by the vacuum, can enter.
This certification guarantees the architect that his/her building is truly passive and hence its energy performance. There is no equivalent guarantee in the case of low-energy buildings.

3. Techniques

In order to achieve the passive standard, various principles must be respected and techniques employed :

Compactness and best possible orientation of the building in order get the maximum benefit from the heat of the sun. Where the orientation is not the best, it is to be compensated for by additional insulation, modifying the size of the windows, etc…

Insulation. Generally, there are between 25 and 35 cm of insulation materials in the walls, 20 cm for flooring and 40 to 45 for roofing, depending on the type of materials used. The windows must be triple-glazed and the frames are specially designed, as is all the woodwork. In addition, the housing is draught-proof. That way, there is very little heat loss through the outer walls, roof and floors.

Ventilation. Ventilation means continuous air exchange with fresh air replacing the polluted or humid air. In passive housing, this is done using a double-flux forced-draught ventilation system. This concept differs from airing, which implies for example the opening of a window for 15 minutes, and the polluted air is then only replaced temporarily. The ventilation of a passive house is closely linked to its draught-proofing. Thanks to the absence of uncontrolled draughts, the occupant can decide him/herself where, when, and how much should be ventilated. That way, the humid or polluted air from the kitchen, bathroom, toilets or the storerooms can be renewed, while fresh air goes through to the living rooms and bedrooms. In that way, there is a continual renewal of fresh air in the house. Heat loss is limited thanks to a ventilation system which allows heat to be recovered. In this system, the warm inside air, which must be extracted, is removed through pipes which are side-by-side with pipes bringing cool air in from the outside. The air flows do not mix, but thanks to a large surface area of contact between the hot and cold air pipes, heat is exchanged with a return of 80 - 90 %. Using a heat pump, the air can be preheated or cooled before it reaches the heat exchanger. Fresh air is drawn in via a long pipe placed 2 metres underground. Thanks to a constant temperature of 10 degrees at that depth, the air is preheated during the winter and pre-cooled during the summer. Using a system by-passing the heat exchanger, fresh air can also be directly blown into the house. The total amount of heating needed for a passive house is so small that a classical installation with radiators or underfloor heating is too great and costly. Supplementary heating on top of the forced-draught ventilation is often sufficient to provide necessary heating throughout the housing unit.

4. Advantages of passive housing

Apart from the energy savings, passive housing offers advantages linked to the well-being of its occupants :

5. Common question

Can you open the windows in passive housing?

There is no restriction or prohibition. A window may, therefore, be opened, just as the doors. If you frequently open your windows during the winter period, the energy needed to heat your house will increase, just as it would for a "traditional" house. By opening your window, you are effectively allowing fresh and cold air into the house, and that air has to be heated. You should be aware that, by installing forced-draught ventilation (system D), new air is brought into the house so ensuring an air quality and maximum comfort for the occupants and, therefore, it is not necessary to open the windows.

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