Combined types of covers are most effective: insulated blinds and shutters, as well as roller blinds, blinds and shutters.
Other studies show, that with windows with high insulation, the effectiveness of temporary blinds decreases significantly. With such low values (biscuit) operational heat transfer coefficients, the window becomes a "positive" collector of solar energy, when the outside temperature is approx. 4- 10°C, and the solar radiation density will be equal 15 W/m2K.
An important problem is the size of window openings in individual facades. Despite the attempts, it was not possible to determine the optimal size (percent) glazing. US data says 0,3 — 0,38 m2/1 m² of the room. Based on the new norm. In low-rise buildings (do 2 storeys), located in i, II and III climatic zones, maksymalny stopień przszklenia dla okien o 2,0<is<2,6 W/m²K ranges from 48 do 52%. It is much smaller for buildings 5- and 11-storey. Considering the phenomena discussed above, "solar architecture" uses minimal, but meeting the psychophysical requirements, glazing to the north, east and west, and maximum from the south.
Experimental tests were carried out at the Building Research Institute, in which the effectiveness of three types of passive solar heating system in Polish conditions was checked. The direct profit system was compared, Trombe wall and greenhouse. The research have shown, that in Polish climatic conditions the system of direct profits is the most effective, and the least efficient Trombe wall. The order is different in other countries.
The direct profit system shows the highest efficiency in our climatic conditions. It is also the simplest and cheapest of the three presented above. However, the other two systems should not be discredited. The greenhouse, despite lower efficiency in small residential buildings, gives a new space, with new interesting functional and architectural properties. Also the Trombe wall, modernized, applying the latest solutions should be tested again. All the studies cited above require a fundamental verification of the views prevailing in the environment of Polish designers regarding the size and importance of the window (especially the southern one) in the building.