Thursday, January 29, 2009

Chat with Adam Stenftenagel

In America, we spend our energy in three broad categories, making products, moving around, and occupying buildings. The building construction and occupation pieces of the pie have been targeted through a number of organizations and standards including USGBC, Energy Star, LEED and HERS. These groups have gradually reduced the occupational and constructive impact of buildings. Later in this post, we'll see just how advanced these buildings have become.

One of the most interesting standards is the Passiv Haus standard being developed in Germany (New York Times article here). A German ex-pat living in the Denver area was so enamored with the idea that he decided he would build an entirely new development based on the Passiv Haus standard just to show us Americans how easy it can be to build well. The development is called GEOS and I was lucky enough to talk about the project and other things with Adam Stenftenagel who runs an energy modeling company called Sustainably Built out of Boulder, Colorado.

The green building movement has begun to coalesce around the slogan "build tight, ventilate right" for good reason. Energy modeling shows that restricting infiltration is by far the best way to reduce energy usage. Standard building codes require a maximum air exchange of 0.35 air switches per hour and a good builder will tighten up a building to 0.1 exchange per hour. To eliminate energy usage entirely, you need to go as low as 0.04 per hours or only one exchange per day.

In addition, buildings in the GEOS development will utilize passive solar heating. The land covenant specifies that no house may cast a shadow on another during the Winter solstice. In a suburban development like GEOS, that means a somewhat unusual checkerboard pattern.
The southern walls of the buildings are full of windows. Carefully placed awnings let in the winter sun for warmth but block out the searing summer rays. The walls and roofs are heavily insulated, R-24 for the total wall systems and R-40 for the roofs.

"Tight" houses have been around for years but suffered from mold problems and stale air due to their insufficient ventilation. The GEOS homes solve the problem elegantly. Low speed fans run constantly, sucking 110 cubic feet or air per second from the bathrooms and kitchen. That air is used to condition outside air being brought into the house in a small heat exchanger located in the basement. That way, very little energy is used to heat or cool incoming air to the desired temperature. In addition, by the time the outside air makes it to the heat exchanger, it has already passed through shallow geothermal tubes running around the foundation, making the heating and cooling processes even more efficient.

These homes are designed to be net-zero energy. That means a somewhat conscious household will have no energy bills over the course of a year. Colorado's generous rebates and sunny weather make solar panels an amazing option. No gas lines will be run and electrical lines will connect the homes to the grid for storage.

In the end, the GEOS development is still a suburb, but it is a vast improvement over standard practice. Their work on the heat exchanger units will likely lead to the development of American Passiv Haus systems comparable to the excellent German ones.

If you are thinking about building a new home/building, it would certainly be worth it to check out some of these innovative homes starting to spring up across the county for ideas. And if you're tired of rising energy bills, it might not be a bad idea to look into the Passive House (into English now...) concepts for the next remodeling project. This page is a must. Depending on your location, you may be able to get financing at a rate that will offset your energy payments and leave you with a more comfortable and sustainable home.

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