Vertical solar-air collectors that are used for providing natural ventilation can be a viable solution in buildings where higher ventilation rate requirements for better indoor air quality cannot be met by traditional natural ventilation methods. Indoor air quality problems have been experienced in Portuguese school buildings where a study revealed that the C02 concentrations in classrooms in winter were higher than the recommended health limits. To improve the environment in these classrooms, solar-induced ventilation has been suggested.

On the base of universally valid laws: energy conservation and the theorem of Fourier, the dynamic behavior of a room is traced back to only two most important parameters. With the aid of the so-called free-run temperature a generally valid strategy for low energy houses is deduced and its transfer to practice illustrated. With the climate surfaces, a planning tool is introduced allowing the strategic planning of low energy houses based on these two parameters. Finally the obsolescence of the passive-solar rules and strategies is demonstrated.