Passive house: exploring the limits to energy efficiency in buildings
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Measurements in the building and simulation results of temperature profiles coincide within 0.2 K and are within the accuracy of the sensors.
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The thermal simulation model based on Fourier’s equation, temperature dependent convective film coefficients and a radiation model give reliable results using the known geometry and the standard material properties (without fitting parametres).
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The buildings perform within the measurement accuracy, reproducing the extraordinarily low heat flows from the preliminary simulation done for the design.
Monitored energy consumption of a 25-year time span
Passive house components of the building envelope
Basic passive house principle | Specific implementation in the Kranichstein project | Validation after 25 years. | |
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1 | Fabric insulation | - Masonry exterior wall with EIFS (see the “Building fabric II: exterior wall structure” section) with >15 mm mineral exterior rendering - Roof: timber construction with beams and blown-in insulation - Concrete floor above the basement insulated underneath | - Sample laboratory testing - Long-term temperatures and humidity measurements |
2 | Avoidance of thermal bridges | - Carefully planned connection details - Thermal separation masonry/basement ceiling | - Thermography |
3 | Airtightness of building envelope | - Carefully planned connection details: plaster, sealant strips, window frames | - Blower door test after 25 years |
4 | Passive house windows (positive energy balance) | - Triple pane low e glazing - Insulated window frames - Deep glazing rebate | - Thermography - Heat-flow measurements - Humidity measurements |
5 | Comfort ventilation with heat recovery | - Large recuperative surface - Ducts with low-pressure losses - Highly efficient ECM ventilators - Particulate filter concept - Noise reduction concept | - Long-term measurements - Pressure-loss measurements - Power balance - Indoor air–quality investigation |
Building fabric I: roof structure
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determined in long-term measurements of the humidity,
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compared to a hygrothermal simulation for the structure (DELPHIN, (Grunewald 1997)) and
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confirmed by testing a sample of the insulation, with a gravimetric determination of moisture in the laboratory.
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the moisture steady state is only reached after 15 to 20 years;
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there was no moisture build-up in the measurements nor in the simulations anywhere in the structure including also at the most critical point (directly beneath the chipboard), the maximal value (in January) was 13.7 mass percent—up to 18% would still be acceptable here (DIN 68800-2 #11.2 2012).
Building fabric II: exterior wall structure
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the insulation material’s raw density; result: 14.92 (± 0.17) kg/m3 (like new),
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materials’ structural load capacity; s10 59 kPa; (like new)
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the EPS’s thermal conductivity, result: 0.0412 (± 0.0012) W/(mK) (like new),
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moisture content: less than 0.5 mass percent everywhere (exceptionally dry).
Building fabric III: avoiding thermal bridges
Building fabric IV: airtightness
Building fabric V: passive house windows with positive energy balance
Triple glazing
Mitigation of spacer thermal bridge
Insulated window frames
Thermal bridge-free and airtight installation of windows
Balanced ventilation with heat recovery
Interior air quality: the top priority goal of ventilation
The duct system: clean thanks to ePM1 80% particulate filters
Hygiene inspection of the ventilation system after 25 years of operation
Summary of hygiene inspection and recommendations
Power consumption and heat recovery rate
Condition of the system
Conclusions
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Excellent insulation (U values less than 0.15 W/(m2K)) on the exterior of building components which was e.g. realised using an established external insulation compound system with just an appropriate thickness; the result is thus typical for a properly designed insulation in this type of masonry construction. The roof insulation is blown in mineral wool in a tilted roof using I-studs.
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Well-planned airtight envelopes, including connections, especially plaster over airtightness films and the use of plaster connection strips and jointing which are the recommended solutions to use in masonry and mixed timber/masonry construction;
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the use of a thick mineral plaster on exterior walls which improves the hygrothermal behaviour and leads to a very long durability; and
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the use of a front ePM1 80% fine particle filter in the heat recovery ventilation system which keeps the whole system clean and allows a long durability providing healthy indoor air.