The passive house concept, or PassivHause (in German), was created and developed in Germany in the late 1980s. This concept emerged when Dr. Wolfgang Feist starts a pilot project in Darmstadt of a set of pioneering houses in the sense of energy saving and environmental sustainability, together with his team.

 In 1996, he ends up founding the Passive House Institute, the body that manages the certification and research activity of buildings constructed using this methodology.

This concept can be explained in a simple way, just think of a house with high thermal efficiency, cleaner air and sustainable construction. However, this process is quite complex, as it follows international standards, which the builder is obliged to follow if they want to obtain certification.

First we need to understand the benefits that a passive house brings to the buyer and the environment. According to Dr. Wolfgang, a passive house can save up to 90% on energy-related expenses and on average up to 75%, using on average less than 1.5L of fuel or 1.5 cubicm of gas to heat one square meter per year. This is partly due to an efficient use of sunlight, the use of special (triple) windows/framework, special insulation of the roof and floor as well as the exterior walls. This insulation is guaranteed thanks to the use of expanded polystyrene blocks, manufactured by Styro Stone. These blocks, which are composed of 3% polystyrene and 97% air (a more sustainable material than traditional materials), make traditional formwork unnecessary, since the block itself performs the formwork and in its middle will be filled with wires of steel and concrete to give the structure strength.

  Finally, an automatic ventilation system is used that will not only regulate and maintain a mild temperature in the house throughout the year, but also provide cleaner and purer air than the outside air due to its filtration system.

The construction according to the Passive House concept is based on five fundamental principles:
 

• Good level of thermal insulation of the opaque envelope;

• Minimization of thermal bridges;

• Air tightness;

• Mechanical ventilation with heat recovery;

• Efficient glazing.

This way of building and rehabilitating has five favorable consequences:

• Excellent indoor air quality;

• Thermal comfort without stratification differentials in height or close to sensitive elements (glazing and thermal bridges);

• Reduced energy consumption (which translates into savings on the electricity bill);

• Absence of anomalies of thermal-hydrothermal origin;

• Durability and build quality.

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Passive house requirements

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• Space Heating Energy Demand must not exceed 15 kWh per square meter of net floor area (treated floor area) per year or 10 W per square meter of peak demand.

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• The Primary Renewable Energy Demand (PER, according to the PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of usable area treated by year for Passive House Classic.

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• In terms of Tightness, a maximum of 0.6 air changes per hour at 50 Pascals of pressure (ACH50), as verified with an on-site pressure test (in both pressurized and depressurized states).

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• Thermal comfort must be achieved in all areas of housing during the winter and summer seasons, with no more than 10% of the hours in a given year above 25 °C. 

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Fundamental principles:

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Thermal insulation

All opaque building components of the house's exterior must be very well insulated. For most cold climates, this means a heat transfer coefficient (U value) of no more than 0.15 W/(m²K), i.e. a maximum of 0.15 watts per degree of temperature difference and per meter. outer surface square are lost.

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passive house windows

Window frames should be well insulated and equipped with low-e glass filled with argon or krypton to prevent heat transfer. For most cold climates, this means a U-value of 0.80 W/(m²K) or less, with g-values around 50% (g-value = total solar transmittance, proportion of solar energy available to the room).

Ventilation heat recovery

Efficient ventilation with heat recovery is critical, allowing for good indoor air quality and saving energy. In the Passive House, at least 75% of the heat from the exhaust air is transferred back to the fresh air via a heat exchanger.

building watertightness

Uncontrolled leakage through spans must be less than 0.6 of the total house volume per hour during a pressure test at 50 Pascal (both pressurized and unpressurized).

Absence of thermal bridges

All edges, corners, connections and penetrations must be planned and executed very carefully to avoid thermal bridges. Thermal bridges that cannot be avoided should be minimized as much as possible.

The Institute provides companies with a planning tool that aims to ensure that a given project meets the necessary requirements to be awarded the passive house certification.

This tool is called Passive House Planning Package (PHPP) and consists of a set of tools and algorithms that allow you to calculate and predict energy efficiency, such as:

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• Energy balance calculation in common Excel format

• Easy and straightforward data entry, flexibly when needed

• Accuracy of the validated result

• Continuously being developed

• Verification for Passive House buildings and EnerPHit retrofits

• Detailed manual with tips for energy efficiency

• Interface for importing/exporting data from/to other programs

• Can be combined with the designPH 3D tool