The 1948 Dover Sun House used phase change materials to store heat

Pioneering solar house was designed and engineered by women

Over the years there have been many attempts and building houses that were heated by the sun; In Passive House + Magazine, Dr. Marc Ó Riain has a fresh look at the Dover Sun House, built in 1948. He notes that "there are two paradigms in low energy building. The first is based on energy replacement technologies and the second is based on energy conservation." We have seen those paradigms play out in the seventies with the "mass and glass" vs super insulation.

Popular Science Cover/via

This house was very much in the first category with a very active solar heating system. Chemical engineer Maria Telkes designed a system relying on a phase-changing material, Glauber's Salt or the decahydrate of sodium sulfate. It is also known as sal mirabilis or miraculous salt, and Telkes tried to do some pretty miraculous things with it. Interestingly, given that it is 1948, this appears to be an all-women project:

Supported by funding from Boston heiress Amelia Peabody, she teamed up with the architect Eleanor Raymond to develop a practical experimental house as a test-bed for the technology in Dover, Massachusetts. The “sun wall chemical heat storage” used double glazing separated from a black metal sheet by an air cavity on the south face of the building.

Popular Science (and it is not the first sun-heated home by a long shot)/via

Anthony Denzer describes the Dover Sun House in detail in his book The Solar House. Originally the tanks of salt were going to be on the ground floor behind glass, but that would block the view, so they put the collectors at the attic level. They are vertical because of worry that snow would collect on them and because they thought it might collect reflections off the snow in winter.

When the temperature of the collector plates hit 100F the fans would turn on and push the hot air down to circulate around the tanks of Glauber salt, which would then melt. Denzer notes that "the only power used by the system was the electricity to run the twelve fans, since no fluids were moved there were no pumps."

Alas, it didn't work very well. Those 12 fans used a lot of power. The Glauber's salt didn't go through the phase change; Denzer writes that "the chemical stratified into solid and liquid layers. In order to work properly, these layers need to mix as they cooled." According to Denzer, a conventional oil furnace was installed in 1953.

However Marc O'Riain concludes that much was learned and the designers went on to greater glory: "Maria Telkes became the first recipient of the Society of Women Engineers achievement award in 1952 and Eleanor Raymond became a fellow of the American Institute of Architects in 1961."

It is all so interesting to see these elaborate experiments in active solar heating that still continue. But as Marc O'Riain notes, there are two paradigms. As Joe Lstiburek has noted: "We were here in the late 1970’s when “mass and glass” took on “super-insulated”. Super-insulated won. And super-insulated won with lousy windows compared to what we have today. What are you folks thinking?"

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