A new methodology to characterize indoor variations of temperature and relative humidity in historical museum buildings for conservation purposes

This paper presents the study of the indoor climate of the Scuola Grande di San Rocco in Venice: it is a 16th-century emblematic example of a historical building. The renowned Tintoretto large paintings magnificently decorate the Scuola. The monitoring and control of microclimatic parameters such as Temperature (T) and Relative Humidity (RH) are pivotal to establish proper conservation policies in museums’ environments. Fragile artworks had been preserved for centuries in “natural climate” conditions, in the framework of historical buildings. In such ambiances, T and RH followed outdoor variations yet mitigated by the hygrothermal inertia of the building. Available indoor climate monitoring protocols consider T and/or RH values, but they do not allow a straightforward comparison of relative fluctuation of T and RH values through time. This paper presents a flexible methodology to visualize T and RH variations. The protocol considers the calculation of time-related index to understand the magnitude of daily (DF) or weekly fluctuations (WF), and the speed of the weekly fluctuations (SWF). The presented method introduces the calculation of climatic excursions index (ICE). The ICE is innovative because it allows us to compare the microclimate of different buildings, and it will enable us to quantify the time in which T and/or RH fluctuate outside reference ranges, even in the case that detailed information on materials and construction methods is lacking. Indoor microclimate variations have been compared with the outdoor ones: this helps to define the hygrothermal inertia of the building.