Earlier this week in Chicago I spoke to the Passive House Alliance, and for them I created a new talk entitled "Superinsulation and the History of the Solar House." It was a full house and I really appreciated the attentive and intelligent audience.
I argued that passive solar heating and superinsulation are fundamentally intertwined, a theme which is probably somewhat sublimated in the book. I based my argument on several key points:
1) In the first "solar house" in 1940, Fred Keck realized, just before construction, that he should quadruple the roof insulation
2) In several early solar houses (most notably Frank Lloyd Wright's 'solar hemicycle' for Herbert and Katherine Jacobs and Keck's Hugh Duncan house), the solar gains were 'defeated' by poor insulation and leaky construction
3) The understanding of thermal mass was crucial to the evolution of the passive solar house
4) By the 1970s, passive solar proponents such as Norman Saunders and William Shurcliff shifted their attention to superinsulation
5) When the Passivhaus movement originated in Germany, its founder (Wolfgang Feist) acknowledged that his ideas had been shaped by earlier examples in North America. Therefore there is a historical continuity between solar house history and the current Passivhaus movement.
I also wanted to show that, when American homebuilders became relatively serious about both passive solar and superinsulation, after 1973, the effects were dramatic. I included the following slide:
At the end of the talk, somebody (intelligently) asked about this statistic. I sympathized with the question, because it does seem too good to be true. Although I recalled this number being cited in Stewart Brand's book How Buildings Learn, I could not remember the original source. I told the questioner that I would be happy to trace it and provide more information.
It turns out I made a mistake by omitting an important qualifier. Here is Brand's statement:
"Between the Energy Crisis of 1973 and 1990, the money spent on space heating in new American buildings dropped by a dramatic 50 percent."
The word "new" was the critical omission. But we still might wonder how the figure is normalized. Brand's source was the article "Energy for Buildings and Homes" by Rick Bevington in Scientific American (September 1990). Bevington's original statement is:
"Space-heating intensity, the amount of heat per unit floor area needed for a comfortable inside temperature, has dropped by almost 50 percent in new U. S. buildings. The decline has resulted from efficiency improvements spurred by the oil embargo of 1973."
I'll be sure to clarify this next time I make such a presentation!
Anyway, I still find the statistic remarkable, and I'd like to find one for residential energy use in general in that period which would encompass passive solar, superinsulation, active solar, tight construction, more efficient furnaces, and President Carter asking citizens to turn down their thermostats and wear a sweater. I have also read the following statement: "Since the 1970s, the amount of energy that Americans use for heating has fallen 40%. This is largely due to improvements in the efficiency of our mechanical systems as well as tighter, better insulated buildings." ("Why Weatherization isn't Enough") But I haven't inquired about the source for that number.
In any case, the positive outcomes in the 1970s are a powerful reminder that Americans can make important changes when they are informed and motivated.
Update (February 2014)
Here's the new slide I use:
(The background image is from The Hawkweed Passive Solar House Book by Rodney Wright.)