Passive House, the fundamentals of high-performance building

In a world where we are facing increasingly growing climate challenges, the construction industry has a duty to design the buildings of tomorrow so that they use less energy, respect the environment, and are more rooted in communities.

The origins of Passive House standards

The Passive House standards, which were born in Germany by the Passive House research institute in Darmstadt in 1990, are the most advanced construction standards when it comes to building efficiency and sustainable construction.

“PassivHaus is a building standard that is truly energy-efficient, comfortable, affordable, and environmentally friendly at the same time. It is not a brand name, but a building concept that can be applied by anyone and who has been proven in practice tests. ”- PASSIPEDIA

But surprisingly, it was in the 1970s in Saskatchewan that the first high-performance building was erected. Since 2000, the PHI US institute has been working on the adaptation of this standard in North America.

Saskatchewan Conservation House, at the origin of the Passive House movement.(Ecohabitation, 2020)

The PassivHaus standard or Maisons Passives in French focuses exclusively on the performance of the building. It’s based on the energy balance concept that measures the energy gains and losses. The main idea is therefore to limit heat and energy losses while maximizing solar gains.  As the use of HVAC* systems, they must be efficient to ensure high comfort while limiting its energy consumption.

figure 1: Fundamental concept of the Passive House standard: the energy balance

"Passive House certified projects are up to 90% more efficient to heat than a project built to meet minimum code requirements". - PassivHaus Institute

The five guiding Passive House principles

To act on this concept of energy balance, there are 5 factors that directly influence the performance of the building.

1- Insulation

Thermal insulation is the first factor that influences the concept of energy balance because it has a direct impact on the building's consumption. In fact, a poorly insulated building sees its internal heat dissipate through these faults (walls, windows, thermal bridges, etc.). These losses are then compensated by the increase in consumption of the heating system of the house. However, in the context of a passive house, the heating/air conditioning consumption must not exceed 15 kWh / m2.year and 30 kWh / m2.year for the PHI Low Energy. The thermal insulation must therefore constitute a continuous and sufficiently insulating envelope around the building.

The consumption of a building does not vary in the same way if we add a thickness of insulation in the walls, the roof, or under the slab. The use of an energy model ( PHPP - Passive House Planning Package ) therefore becomes predominant in order to optimize the addition of insulation.

 

2- Sealing

Limiting heat loss also requires good airtightness. Like insulation, waterproofing must form a continuous envelope around the building. The tightness of a building is measured using a blower test which calculates the number of air changes per hour. This value should not exceed 0.6 CAH (Air Change Per Hour) @ 50 Pa. In other words, a high value in this test indicates the presence of faults in the enclosure. Several experts also agree that carrying out several tests of this type during the construction phase makes it possible to plug these failures.

Finally, the problem of humidity is resolved by the use of a smart air and vapor control membrane ( Siga - Majrex ) installed on the warm side of the wall which allows the wall to dry from the outside while making the infiltration of humidity from inside the house impossible.

3 - Thermal bridges

Thermal bridges are due to the assembly of structural elements having high thermal conductivity and perforating the building envelope. They then become an important vector for heat transfer, and therefore energy loss.

Thermal bridges (The house of works, 2016)

The previous section shows the operation of a thermal bridge here represented by the floor. It thus allows the heat, attracted by the outside (colder zone), to pass through the wall. In addition to being responsible for heat leaks, thermal bridges are also the source of significant risks of condensation. In order to identify them, the design phase is important. It allows them to be eliminated or to find mitigation methods when the first solution is not possible.

 In this regard, no explicit constraint is mentioned by the standard, but the idea is always based on the principle of energy balance: "the less energy we lose, the less we have to add”.

4 - Glazing surfaces

Windows are one of the most important construction detail in PH design because it can reduce the building heating and cooling demand by 85%. Generally known to create interruptions and bridges in the envelope, Passive House efficient glazing is used to absorb the sun's heat and naturally warm the building during the winter. During summer, window shading systems will help keep the building cool. In our climate and region, in order to gain maximum solar gain, windows should ideally be south-facing.

During the design phase, PH designers will take into account the building orientation, climate data, seasonal considerations, and architectural requirements to come up with the most efficient plan for windows.

However, choosing a window certified by the standard does not guarantee optimal results. Indeed, the installation method as well as the materials used to seal the opening of the windows ( Siga Wigluv , Huber Engineer flashing tape ), are just as important in order to compensate for the interruption in the building envelope.

5- Heating & cooling system (HVAC)

Finally, the last important factor concerns the ventilation of the building. Indeed, the 4th factors mainly influence the reduction of energy losses. However, once isolated and therefore "cut off from the outside world", a home must be equipped with efficient and high-performance ventilation equipment, effective because the Passive House standard only allows a maximum heating consumption of 15 kWh / m2.year (idem for consumption in air conditioning). The system must therefore be efficient in terms of energy recovery. Thus, it is generally a question of an energy recovery system (ERV) that ensures a transfer (up to 'at least 75%) of the heat from stale air to fresh air. This type of system ensures significant ambient air quality, which is predominant in a health context as we know it.

Companies such as Zehnder America or closer to us, Minotair ( Pentacare-V12 ) have developed products capable of meeting such performance criteria.

The Passive House standard thus represents the highest performance building standards. These ambitious standards should pave the way for a deeper reflection on construction to achieve the 2030 climate targets.

In our next article, we will show you the differences between the different types of construction, from code houses to passive construction house.