Optimisation of insulation and solar control strategies as function of building’s intended use in the retrofit of massive buildings

In temperate climates, such as most Italian ones, the need to limit both winter heat losses of buildings and their overheating in other periods is present. The second requirement is particularly relevant in the presence of high internal and solar gains. In these climates, it is not convenient to exceed the insulation thickness. Therefore, when the energy renovation of an old building with heavy masonry is performed it is a question of optimizing the position (internal or external) and the thickness of the additional insulation. Another question is the choice of a solar control strategy, if extended glazed surfaces are present. Both of these problems are present in old Italian public buildings, particularly in schools. This paper presents a computerized methodology for optimizing these choices. The case study consists in a typical school building from the early 1900s with a heavy structure and large glass surfaces in a climate of Northern Italy (Bologna), with cold winter and hot summer. The results show that the external insulation is the best performing, and that there is an optimal thickness when the building is a school. If the building is reused for offices, due to the lower internal gains, the energy convenience of the external insulation increases, but its optimal thickness becomes excessive. Small slats inserted between the glasses are the best performing solar control device from both an energy and visual comfort point of view; on the other hand, the external slats provide better thermal comfort in the warmer period.