The Passivhaus movement was developed by Swedish professor Bo Adamson and German professor Wolfgang Feist in 1988. They developed a realistic method of building using super efficient materials and efficient concepts that saves 80-90% of home heating costs as compared to conventional new home construction. The first passive house was built in Germany in 1991, now with about 25,000 houses worldwide. Passivhaus is now the world standard in energy efficient construction regardless of climate and location. For a house to be considered "passive" it must incorporate specific building characteristics including the majority of heating from the sun, a super insulated and airtight shell and mechanical air ventilation to achieve a specific volume/hour of air exchange. To be considered "passivhaus certified" (not to be confused with net-zero homes) the heating load must not exceed 15 kWh/m2 per year. The Passivhaus Institute certifies building products which meet or exceed their efficiency standards. Additionally, they have developed a powerful software called PHPP (passive house planning package), a highly accurate energy modeling tool used to calculate the energy requirements of any structure (accuracy of +/- 0.5 kWh).
Eight Building Principles (all to be explained further in future posts)
1. Super Insulation: significantly reduces heat transfer between the inside and outside of the home. High R-values (conversely, low U-values) resist the flow of heat down the temperature gradient. Not only are walls and ceilings considered, but at the ground level and windows as well.
2. Super Airtight Envelope: very simple-if air is allowed to move back and forth, heat is lost. At least 40% of a home's heat is lost through ventilation (ie. leaks) even in new construction! But doesn't a house need to "breathe"? Sure it does, but I want to know exactly where it is breathing.
3. Thermal Bridging: a thermal break is needing to separate the cold to hot surfaces. The best insulated wall in the world will transfer heat if thermal bridging is not considered.
4. Heat Recovery: 90% of the heat from the air that mechanically moved out of the house is recovered and brought back into the house. The energy transfer is reversed in the summer, keeping the house cool.
5. Mechanical Ventilation: related with #3. Because the house is virtually airtight, it needs to breathe to maintain proper humidity levels. New super high efficient air exchange units (that recover the heat-see above) move the entire home's volume of air in a number of hours, replacing it with fresh outside air and virtually uses no electricity to do so.
6. Highly Insulated Windows: one of the building criteria that people think they are achieving but in fact are not. There are many window companies that provide surprisingly high R-values (upwards of R-12), unfortunately none of which are manufactured here in the United States. Certain Energy Star certified windows insulate well (for a limited lifespan-more on this later) but do not let enough solar heat through the glass to provide the necessary heating from the sun. This is not to mention specific glazing and frame insulation options.
7. Energy Modeling: using the PHPP modeling software, the efficiency of a design can be calculated before it's built with astounding accuracy. Prediction of energy usage is a vital component in the design process.
8. Passive Solar Gains: amazing to me to see new homes facing completely the wrong way or having too many windows on the northern exposure. The home requires many insulated windows on the south facing side and limited windows on the west and north sides. Conversely, avoiding overheating in the summer with planned shading/overhangs.
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