Solar chimneys - hot air that cools

Reader Mike Pulskamp left a comment on a recent blog about the concept of passive housing. He noted that the sealed envelope method of this housing can pose some problems for air quality.

He said that solar chimneys are a great option for green home builders. I've read about solar chimneys but never seen one in action. The basic concept is that a solar chimney absorbs heat, pulling cool air through a structure and up into the chimney (see image). That simple act of ventilation helps cool a home. These have been in use around the world for centuries. In hot windless areas, solar chimneys are sometimes the only source of ventilation.

I'm no home builder, but one day I'd love to build a house that is off the grid - or at least nearly so. It's so great to continue to learn how old concepts can be put to use in modern forms.

Here's another variation on the concept that's actually in use at Zion National Park's visitor center. This variation is a passive, evaporative downdraft cool tower.

Passive houses - another innovation from the Germans

I saw this interesting headline on NYTimes.com about passive houses.

This is a new concept to me, and probably to most Americans. Such houses "get all the heat and hot water they need from the amount of energy that would be needed to run a hair dryer," according to the article.

"Using ultrathick insulation and complex doors and windows, the architect engineers a home encased in an airtight shell, so that barely any heat escapes and barely any cold seeps in. That means a passive house can be warmed not only by the sun, but also by the heat from appliances and even from occupants’ bodies," the article continues.

The idea was pioneered in Darmstadt, Germany, a city of 140,000 outside of Frankfurt.

So far the idea has not gained much traction in the United States. One is being built in California, but most of the materials needed for this unique kind of construction must be imported, making it a costly endeavor. Passive houses cost only about 5-7% more than conventional housing in Germany, where the materials are increasingly available off the shelf.

The other challenge for adopting this housing style - at least for most of America - is that no one has figured out how to turn the warmth generated by the house into coolness. The concept is great for mostly cold areas that do not require air conditioning. In the Midwest, where summers get hot and humid, we need our creature comforts.

A final obstacle to adoption here is America's addiction to personal space. Passive houses work best when limited to about 500 square feet per occupant. That doesn't jibe with a McMansion culture.

Obstacles aside, passive housing strikes me as an innovation worth pursuing. I'm sure some bright minds can find a way to keep passive houses cool as well as warm.

If the idea can be melded with straw-bale construction, we'd have a very green new home movement waiting in the wings.