A house using direct radiation should act as a sun catcher. The sun's rays should penetrate to its interior as much as possible and be absorbed there by the internal elements of the structure, tj.; ceilings, floors and walls. Materials for the construction of internal partitions should have a high heat capacity.
The material that allows the sun's rays to penetrate inside the house is glass. Used for hundreds of years, it is constantly smelted from the same materials, namely: quartz sand, soda, dolomites, limestone and additives that give specific properties.
Windows and glazed surfaces in the building were always intended to illuminate the interior, enabling visual contact with the outside world and letting in the beneficial rays of the sun. Moreover, they constituted a transparent cover against the external atmospheric influence. Architects treat the window opening as one of the basic elements of the architectural composition. For centuries, the shape of the hole, or a glass plane, as opposed to a full wall, it was a determinant of changing epochs and architectural styles.
Dozens of glass types are produced, that can perform many different functions, but for passive systems, the types of glass that let the maximum amount of light and sunlight into the interior are the most interesting, and stopping the penetration of heat rays to the outside.
Such properties have ordinary window glass, which, after a few improvements, becomes a highly efficient solar collector (lower iron oxide content, anti-reflective coatings, selective layers). Glass allows solar radiation to penetrate into the building in almost the entire width of the spectrum (without part of the ultraviolet radiation) from 0,3 μm do 3 μm, a stops long-wave infrared radiation (thermal) with a wavelength above 3 μm. This phenomenon is known as the greenhouse effect, or greenhouse. Naturally, heat is transferred outside through window openings not only by radiation, but also by conduction or convection of air, as well as by permeation.