The Air Force Academy solar house

Source: https://catalog.archives.gov/id/6346814

It's little known, but coming to light now as historical government documents are digitized: the United States Air Force Academy developed a solar house experiment in 1975.  It was not a purpose-built work of architecture, but rather a retrofit of an ordinary military housing unit.  They called it the Solar Test House.

The existing house was called a "Capehart unit," and it was among more than 1200 such units built by the Academy in 1958-59 in Pine Valley and Douglass Valley (on the USAFA campus).  Though there were several variations, the typical Capehart unit consisted of 3 bedrooms and 2 baths on about 1200 square feet on ground level, with a 700 square-foot basement.  The units had uninsulated brick walls (R-1) and "extensive air infiltration."  On average, each Capehart unit was estimated to need 30,000 Btu/Hr. each year.  With these factors, plus the excellent solar resource in Colorado Springs, it is easy to see why the Air Force Academy saw solar heating as an opportunity to manage energy costs.

The Solar Test House was also motivated by another set of historical contingencies.  Work on this project began in 1973, shortly after a crisis.  In the winter of 1972, Colorado experienced a shortage of natural gas, and the Air Force Academy was cut off for nearly six months.  (They used fuel oil, at great expense.)  Additionally, President Nixon announced "Project Independence" in June 1973, which aimed for national energy self-sufficiency by the mid 1980's, and the Air Force project was meant to contribute to this larger effort.

The solar heating system was rather conventional, consisting principally of 28 water-type flat-plate collectors manufactured by Revere.  Air Force researchers considered the design "unique" because, while half of the collectors were placed in a fixed array on the roof (at a 52˚ tilt angle), the other half were mounted on a ground array with adjustable tilt angles.  Apart from the ground array, the schematic design shown below strongly resembled earlier systems, especially MIT solar house IV (1957).  Extensive plumbing was required.  Also of note is that the 2500-gallon concrete storage tank was placed underground (outside the house) "for aesthetic considerations."  It was not insulated.

Aesthetically, there is not much of interest here, and architectural design is not mentioned in the official project reports.  Presumably the design was executed by the Academy's Department of Civil Engineering.  The major feature of the design is the addition of a solar roof form added to the existing standard roof of the Capehart unit.  Because these roofs follow different geometric logics and produce asymmetry, the result is somewhat incongruous, if rational.  In the larger history of solar houses, the eccentrically-shaped roof is a recurring theme; here that theme is not interestingly explored or well-resolved.

The researchers considered the Test House "a working solar energy laboratory" and modified it over a period of years.  In February 1977 they focused on efficiency, adding vestibules on the doors and urea formaldehyde (UF) foam insulation in the walls and ceilings.  (The safety of UF was the subject of much discussion at this time; the Air Force project found no harmful off-gassing.)

In late 1978 they installed evacuated tube collectors on the ground array.  These were found to be "not as effective as flat plate collectors," and more expensive.

How did the house perform?  The insulation reduced the heating load by 27%.  After that reduction, the solar heating system could provide 49% of the house's heating needs.  These figures were considered very reliable because the researchers also instrumented an identical Capehart unit as a Control House.

Then in February 1979 the researchers "decided to operate the house as though it had been completely cut off from natural gas."  (The solar heating system did depend on electricity.)  They found that the indoor temperature only fell below 60˚F twice, for short intervals. They wrote: "Therefore, a solar home occupant can survive relatively comfortably during winter weather until the supply of auxiliary energy is restored."  Clearly the themes of crisis and independence underscored the discourse about the project.

More broadly, Air Force Academy researchers concluded that the "new and growing" commercial solar industry could supply all the necessary hardware for such a system.  But the equipment was expensive: "In a competitive economic environment with conventional fossil fuels, solar energy presently falls somewhat short."

Some Air Force reports available on the web are linked on the Resources page.

Why I care about Building Science

Building Science, summarized simply, is the study of heat, air and moisture movement through walls, floors and roofs.  In Europe it's called Building Physics.  Building Science experts work to make buildings more energy-efficient, healthy, and durable.  They know about types of foam, and vapor retarders, and pressure differentials.

Most architectural historians don't pay much attention to Building Science.  They care about buildings' narrative meanings.  They like to 'read' and interpret buildings much like literary scholars like to read and interpret texts.  They don't like to study heat transfer.

I prefer to read and interpret buildings too.  I love to discover spaces that have rich layers of meaning, such as William Alexander's Halliburton house.  I enjoy offering new ways of seeing important buildings, such as my look at the gravity-defying details in Kahn's Kimbell Art Museum (pdf).  And a primary interest remains: how are social relationships constructed and reflected in modern housing?  To talk about r-values and roof overhangs might seem pedestrian by comparison. 

So why do I care about Building Science?  I think I can explain it best by analogy: to be an architectural historian interested in Building Science is like being an art historian interested in picture frames.  Imagine an art historian walking through the Louvre and examining the surrounds rather than studying and interpreting the content of the paintings.  You'd wonder about that person's good judgment.

Now imagine every picture frame in the Louvre was clearly wrong in some manner—out-of-square, or built of a material which damaged the painting, or prone to falling off the wall.  In that context, you'd understand why an art historian would be curious about the history of picture frames, and why they were made that way.

To study the canon of 20th-century architecture is like walking through a Louvre full of paintings in broken frames.  Take the Farnsworth house: the (immensely interesting) content is, for me at least, overshadowed by the fact that the building simply did not work as a building.  Ice formed on the inside of the walls, the space overheated in summer.  This is hardly an exceptional story.  By 1960 James Marston Fitch noticed that "the modern architect [is] quite removed from any direct experience with climatic and geographic cause-and-effect."

Eventually you get more interested in the frame-making than the content of the picture.  And pretty soon you find a few people who advocated for better picture frames, and then some people who used new methods to make picture frames correctly, and finally the very rare figures who understood that the making of the frame was in fact integral to the making of meaning within the frame.  You begin to see that it's impossible to separate the picture and the frame.  You want to honor the people who figured out how to do it right.

In other words, I care about Building Science because I need to care about it in order to understand and explain 20th-century architecture properly.

Solar Geometry in France, 1961

Even though it's becoming more and more common to find architectural historians recognizing that environmental concerns were central to the history of modern architecture, the subject of solar heating seems a bit recondite for an institution such as the Cité de l'Architecture et du Patrimoine, the major museum of architecture in Paris, which features full-scale Romanesque portals and Gothic sculptures.  So I was surprised to find these solar geometry diagrams on display:

At the museum, the caption read: "Diagrammes solaires C.S.T.B." and no date was given.

C.S.T.B. refers to the Centre Scientifique et Technique du Bâtiment, France's national agency for building science research, then and now.  After some further exploration, I believe these diagrams were first published in 1961.  The C.S.T.B. researchers, Pierrette Chauvel and Jean Dourgnon, appear to have been important figures in lighting and daylighting research.

Also of note in the image above: the curved lines are at monthly intervals, with the exception of dashed line, which indicates March 13-October 1.  I'm not sure why that would have been a significant date.  Please comment if you have some insight.

The diagrams were included in a section entitled: "Protectrice et Climatique: Les Vertus de L'Enveloppe."  Here is the explanatory text:

L'une des premières fonctions de l'architecture est de protéger ses utilisateurs du climat extérieur.  Une température agréable et constante s'obtient par le choix des magrtériaux de construction, par la conception même du bâtiment et de son enveloppe et, plus récemment, par l'usage de l'air conditionné.

Aux xxe siècle, la façade en verre devient une réalité.  Les baies vitrées offrent des vues plus larges sur l'extérieur et une nouvelle perception de l'espace mais laissent entrer une trop grande quantité de rayons solaires.  Dans les années 1950, les brise-soleil apportent une solution technique tout en dotant la façade de nouvelles qualités plastiques.

Aujourd'hui, la sensibilisation aux problèmes environnementaux conduit à concevoir une architecture dite <<écologique>>.  Le traitement de la <<peau>> entre alors en ligne de compte comme la question des économies d'énergie.

And here as I've translated:

Protection and Climate: The Virtues of the Envelope

One of the primary functions of architecture is to protect users from the weather.  A pleasant and constant temperature may be achieved by the choice of building materials, by the design of the building and its envelope, and, more recently, by the use of air conditioning.

In the twentieth century, the glass facade became a reality.  Windows offered a greater views of the outside and a new perception of space but let in too much solar heat.  In the 1950s, the brise-soleil provided a technical solution while giving the facade new plastic qualities.

Today, an awareness of environmental problems has prompted an architecture called "ecological."  The treatment of the "skin" then engages the question of energy savings.

In essence, the point of the exhibit is that French modern architects (like Le Corbusier) learned that all-glass structures overheated badly, and that knowledge of solar geometry was needed for proper shading --- a major theme in 20th century architecture as I explain in The Solar House.

If diagrams such as those above were only available to French architects beginning in 1961 (and I'm not sure that's the case), then they were a few decades behind.  American architects had access to this kind of information in 1938.  (See Whit Smith's solar tool.)

Solar Futures: The View from 1973

The history of solar energy is full of lofty goals or aims that were not realized.  Here's an example from 1973:

"Although the sun is the indirect source of all fossil fuels, it has been neglected as a direct source of power. Yet the potential is tremendous: The energy in the sunlight falling on the surface of Lake Erie in a single day is greater than the entire nation's present annual energy consumption.

In recommending a large research effort in solar energy, a joint panel of the National Science Foundation and the National Aeronautics and Space Administration reported last December that by the year 2020 the sun could provide 35 per cent of heating and cooling in buildings, 30 per cent of the nation’s gaseous fuels and 20 per cent of its electricity."

---New York Times, April 18, 1973

(The "large research effort" never occurred, and solar energy currently accounts for 0.32% of US energy use according to Lawrence Livermore National Lab, although I do not believe this figure includes passive solar heating --- see The Clothesline Paradox.)

Jørn Utzon's sun-responsive houses

Here's an extremely interesting academic paper that was published recently:

"Utzon and the sun path as an organizing element of life in a house"
by Miguel Ángel Rupérez Escribano, Universidad Politécnica de Madrid
Fourth International Utzon Symposium (2014)
Link to pdf

Danish architect Jørn Utzon is best-known, of course, for the design of the Sydney Opera house (and for the fractious collaboration with engineers from Ove Arup's office on that project).  His Bagsværd Church (Bagsværd, Denmark, 1968-76) is also a masterpiece of world architecture in the late-modern period.  What may be less well-known is that Utzon designed dozens of houses around the world.

Utzon's own house, Hellebæk, Denmark (1950-52)
Photo by Seier+Seier
www.flickr.com/photos/seier/2472346988/

If you're thinking that the image above looks quite a bit like George Fred Keck's solar houses of the 1940s, you're right, it certainly does. Escribano concludes that Utzon was influenced by some of the main characters in The Solar House, particularly Keck and Frank Lloyd Wright:

"The selected houses designed by Utzon follow a common pattern, which has remarkable similarities with the American solar houses."

Escribano's excellent study goes further, looking closely at how Utzon adjusted the solar orientation of many of his homes to the southeast or southwest based on site and climate factors.

Orientation of 20 houses by Utzon.
From the article linked above.  Drawings by the author.

Although Escribano says that Utzon considered the sun "a useful element in heating the house" in cold climates, the paper does not suggest that Utzon aimed to quantify energy savings, or to call his houses "solar," as Keck and Wright did.