Retrofit of Italian School Buildings : the Influence of Thermal Inertia and Solar Gains on Energy : Demand and Comfort

Most of the Italian school buildings were built before the 1973 energy crisis, so they need a retrofit to reduce their primary energy demand and improve indoor environment quality. Moreover, regardless of age, these buildings are equipped with large windows; therefore, it is generally necessary to improve the solar control strategy by means of more recent devices and technologies, in order to ensure the conditions of thermal and visual comfort while reducing the energy demand. Furthermore, the older buildings have heavy masonry, in these cases the problem is where it is more convenient to place an additional layer of insulation: inside or outside the buildings opaque envelope elements. This work is aimed to explore, only by means of computer simulations, the effects of various retrofit strategies on energy demand and general comfort conditions. A specific homemade software has been used. The examined strategies are characterized by different positions of the additional insulation and various solar control devices. At present, the case studies consist in two school buildings in the city of Bologna in Northern Italy. In order to assess the influence of internal gains and time profile of use, other possible uses for the same buildings, such as offices or dwellings, have been considered. Simulations results show that the external insulation is always the most performing, but the differences with the internal one are not relevant in the case of the classrooms. The differences increase with the reduction of internal gains and the extension of the daily time of use, therefore with the use as an office and even more with that as a dwelling. The use of slats inserted between glasses to control solar radiation can be proposed in any case and is useful for improving the luminous comfort, without significantly changing the energy demand for lighting, and consequently for cooling. Compared to this type of device, external slats provide less luminous comfort but better thermal comfort in the cooling period, however they reduce incoming luminous flux and involve a remarkable increase in energy demand, furthermore they cannot be proposed in a historical urban context.