The next step in sustainable building: the Passive House
Pat Murphy is the Executive Director of Community Solutions. He is the author of the 'Plan C: Community Survival Strategies for Peak Oil and Climate Change' (2008), and co-wrote and co-produced the award-winning documentary film, "The Power of Community: How Cuba Survived Peak Oil" (2006). He has extensive construction experience and developed low energy buildings during the nation's first oil crisis. Pat is a founding member of the board of the Passive House Institute US.
The world must reduce its carbon dioxide (CO2) emissions significantly, in the range of eighty to ninety percent over the next few decades.1 Every use of energy is now under review, and we are finding that the greatest generators of CO2 are not automobiles and airplanes but buildings. As a result, developers, architects, and planners are looking for ways to build structures that use significantly less energy than even the top-rated "green" buildings of today.
Originated in Germany in 1991, "Passive House" (Passivhaus2) design may well be the only currently-available building sector solution that can achieve the needed CO2 emissions reductions. Unlike conventional "green building" standards like LEED and Energy Star,3 Passive House design focuses on aggressively reducing overall requirements for heating and cooling through built-in energy conservation measures.
The core of the Passive Houses approach is the use of ultra-thick insulation and highly-insulating doors and windows to create a nearly airtight building envelope. Combined with a relatively simple heat-exchanging air system, the Passive House allows barely any heat or cold to seep in or out, while maintaining fresh and even-temperature indoor air quality. A Passive House can be heated almost entirely by the sunlight coming through the windows, the heat from appliances, and even the heat from occupants' bodies (thus the term "passive," as a central heating system is not required).
The energy savings delivered by Passive House structures are sufficient to make up for most of the added costs. Figure 1 (reading right to left) shows that as the cost of Passive House upgrades goes up, the heating energy needed goes down—to the point where central heating and cooling systems can be eliminated (at about 15kWh/m2 as in the Figure), freeing up financial resources for better windows, more insulation, and other Passive House components.
Indoor air quality can be a problem when buildings are designed to be airtight. To address this issue, Passive Houses include a low-energy central ventilation system that allows the heat in warm outgoing air to be transferred to colder incoming air, with up to 90 percent efficiency in the winter; the reverse process occurs in the summer.
Passive House methods have been used to construct and renovate over 15,000 single-family, multi-family, commercial, and institutional buildings around the world, largely in Europe. The method has proven so successful that the European Union is considering adopting Passive House standards for all new buildings.4 Thanks to steadily growing demand, construction costs are shrinking; in Germany, new Passive House structures cost only about 5 to 7 percent more to build than similar structures using conventional methods.5
Unfortunately, the U.S. has been much slower than Europe to adopt energy efficiency goals; domestic design and construction practices will need time to catch up to where Europe is today. As a result, even the "green buildings" being constructed today may require considerable retrofits to meet the future standards required for carbon emissions reductions. Passive House buildings are achieving that standard now.
1 Martin Parry, Jean Palutikof, Clair Hanson & Jason Lowe, "Squaring up to Realty," Nature Publishing Group, May 29, 2008.
2 Unlike the the English word house, which generally implies a single-family residence, the German word haus can be applied to any building that serves as a dwelling for people, and in some cases can be loosely applied to non-residential buildings.
4 European Parliament, Resolution of January, 31 2008 on Action Plan for Energy Efficiency: Realising the Potential.
5 Elisabeth Rodenthal, "No Furnaces but Heat Aplenty in 'Passive Houses'," New York Times, December 26, 2008.
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