The Artistic Glass of S. Somenico’s Basilica in Perugia: Measurements and Simulation of the Micro-Climate Conditions.

The works of art preservation is in Italy an argument of great interest, because of its wide historical-artistic heritage. An important role in the preservation is due to the micro-climate conditions, over all for those works of art sensitive to temperature, solar radiation, relative humidity absolute values and variations. Artistic windows are sensitive to temperature variations, caused by the micro-climate conditions and solar radiation, but also by relative humidity. Particularly sensitive are the painted artistic glasses, such as the ones in the S. Domenico’s Basilica in Perugia (Italy). The glass was built in 1411 and in this period a restoration process is going on; the restoration concerns with the stone construction and the glasses. A preliminary study of the problem is the aim of the present paper; the microclimate conditions (internal air temperature and relative humidity, external air temperature and relative humidity, solar radiation) in the S. Domenico’s Basilica were measured, in the period January 2003 - June 2004; data were elaborated and compared with the optimal values of temperature and relative humidity given by UNI 10829 and the Risk Index in the worst conditions for the glass was evaluated. The Risk Index is the percentage of time, during a month, in which the values of each parameter (temperature, temperature daily and hourly variations, relative humidity, relative humidity daily hourly variations) are outside the optimal values range. A numerical simulation of the surface temperature distribution over the glass was carried out, by means of Fluent 5.4 Calculation Code, in order to consider the temperature difference between different points of the glass; the measured data and other statistic data given by the Literature were used as inputs. The surface temperature of the glass was calculated in many points and a map was obtained. Absolute values and daily variations were considered, and the Risk Index, in compliance with UNI 10829, was calculated. Results showed high risk index values, over all in the cold season; the daily temperature variations are always outside the optimal values range. So the preliminary analysis of the micro-climate conditions in the S. Domenico’s Basilica showed it is necessary to protect the artistic glass after restoration, in order to reduce the damaging risk due to the environmental conditions.