In the early 1940s, the American engineer George O. G. Lôf (1913-2009) decided to revolutionise the approach to solar heating by replacing the water-based systems that were favoured at the time, but which were restrictive (corrosion, etc.), with simpler, but less thermally efficient, air-based systems. He developed an air collector, made from sheets of blackened glass exposed behind glass in a box. In good weather, this collector allows him to reach temperatures of 80°C. He decided to install it in his Colorado home and combine it with stone storage, which provided more than half of his heating needs. This system was then disseminated, improved and integrated into many passive solar buildings in the United States, as well as in France from the early 1970s.
Although it has been forgotten, the principle of air collectors without inertia is today recommended by certain design offices for the preheating of new air.
