The term Passivhaus, passive house in german, refers to an architecture that, through its design, uses the energy and climate of its environment to obtain comfortable conditions inside the building without the need to use active heating or cooling systems.
These buildings are characterized by having a position and orientation that allow the sun to be the main source of heating. The rest of the energy needed for air conditioning can be easily covered with renewable energy collection systems and very low energy consumption, reaching savings 70-80% compared to a conventional late twentieth century building.
To achieve these goals, there are 6 concepts that need to be considered and implemented from the earliest stages of an architectural project.
1- Optimal thermal isolation
Buildings need to be thermally isolated from the outside environment in order to offer comfort to their users. Generally, a passive building has more isolation in its external enclosures (thermal envelope) than a conventional one, exceeding what is demanded by current regulations.
2- High performance windows
It would be useless to have a very well isolated façade if the windows do not provide us with high thermal protection and airtightness.
Using frames and glasses with very low thermal transmittances very low energy is lost throught the weakest points of the envelope. On the other hand, the glasses can be configured to control the amount of solar radiation that crosses inwards, managing the overheating of the building during the summer.
3- Absence of thermal bridges
A thermal bridge is a unique point in the thermal envelope of the building, either because of its geometry or because of changes in its composition. This singularity increases the energy flow compared to the rest of the envelope and will therefore be a place where we lose heat in the winter or gain heat in the summer. Passive design seeks to minimize these thermal bridges and measure them to ensure that energy loss is kept to a minimum.
4- High airtightness
A great energy loss factor in conventional buildings is air infiltration. In other words, this happens in places of the envelope through which air from the outside enters the interior causing a gradually loss of the energy used to air conditioning. That is why passive buildings seek to have a very airtight envelope, so that these infiltrations are minimal.
To check airtightness, a Blower Door test is performed, using a fan installed on the access door of the building which generates a pressure difference of 50 Pascals (Pa) between inside and outside of the building and measures the volume of air it is blowing compared to the indoor air volume.
This volume ratio is measured in renovations per hour(ren/h). In passive buildings, the airtightness is around 0.6 ren/h, while in conventional buildings this airtightness is usually between 6 and 10 ren/h, which means about 10 times more air infiltrations and energy loss.
5- Mechanical ventilation with heat recovery
Although the envelope is very airtight, in order to ensure a healthy environment inside, the air must be renewed, so vitiated air must be expeled while fresh air is introduced inside the bulding.
In order to do this renovation without losing the energy, a mechanical ventilation with heat recovery system is needed. This allows us to pass some energy from the indoor air to the fresh air that we introduce in the building but without mixing them. For example, if the indoor air is at 20ºC and the outside at 5ºC, the system will introduce the outdoor fresh aire around 17ºC.
This system is usually operating 24 hours a day, which, at the same time, offers an indoor air with healthy CO2 concentrations even if the building is in a large city. In addition, the system has filters that prevent the entry of pollution, dust, pollen and other suspended particles.
6- Sun protection
In locations such as Catalonia or Spain, it is important to design sun protection elements correctly. Without them, the building would need to be continuously cooled during the summer season because solar radiation would heat the inside and the thermal envelope would not allow this heat to dissipate. Sun protection strategies must prevent the sun from entering during the summer and allowing it to enter during the winter in order to take advantage of its heat input.
All these factors, combined with each other, allow a building to need very little energy for its operation while achieving healthy interior conditions and a high level of comfort.
The Passivhaus Certification was born in Germany in 1996 with the founding of the Passivhaus-Institut. This entity is responsible for verifying that a building meets the necessary conditions to obtain certification. The Passivhaus seal guarantees a high quality in the construction of the building and assures energy saving, indoor comfort and a healthy environment. The procedure is carried out through a certification company that monitors the building during the project and execution phase and acts as an intermediary with the Passivhaus-Institut.
The criteria to be met in order to obtain the certification are the following:
PRIMARY POWER DEMAND
On the other hand, the institute also promotes the training of technicians so that they can properly design a passive building. The PassivHaus Designer seal guarantees that each technician has the necessary knowledge to develop a project that meets all the above criteria.
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