Diurnal Variation of Solar Radiation on Differently Oriented Surfaces of Monuments

In the Northern Hemisphere and, in particular, at 6 different latitudes (38-degrees, 42-degrees, 45-degrees, 48-degrees, 50-degrees, 56-degrees) the flux of solar radiation which hits the vertical surfaces orientated in the eight main directions (North, North-East, East, South-East, South, South-West, West, North-West) has been computed and compared with the horizontal plane, at the time of the summer and winter solstices and equinoxes. This study has been carried out with the aim of furnishing a useful basis to calculate the quantity of energy which hits a surface, as an integral to find out when the maximum energy hits it, and to determine the time interval, during the day, during which a work of art is directly exposed to solar radiation. All this information is useful, in that solar radiation is an important forcing agent, and necessary in the biological and physico-chemical processes which lead to the degradation of a work of art. Furthermore, it is also useful for the management of the rooms or the environment around the monument, to know whether it is situated inside or outside. Therefore, the amount of energy reaching the various vertical surfaces has been compared to the amount of the energy received by the horizontal planes and which are normally acquired at the various monitoring stations. Moreover, the efficiency of the model depends on the correct choice of the atmospheric transmission coefficient alpha. Finally, some examples of the partial results obtained when such a model was applied to the Scrovegni Chapel, the Sistine Chapel, the Cathedral at Orvieto, the Horses of St. Mark in Venice and the Trajan Column, will be given.