## 2 Materials and Methods
### Data Analysis  
The monitored data were statistically analyzed and compared in terms of the following:  
* Average values over the selected period, i.e., monthly and yearly;
* Hourly values for defining the statistical limits included in the 93 rd and seventh percentiles, to exclude the largest and riskiest fluctuations;
* Short-term fluctuations, i.e., 24 h.  
In addition, the trends of T and RH values were evaluated and shown in the graphics of the \"performance index\" (PI) for each zone. This index allows the assessment of the indoor microclimatic conditions in relation to the conservation capability of the object exhibited inside the zone. Indeed, it represents the percentage of time during which the evaluated microclimate parameters fall within the \"acceptable\" ranges [41]. Therefore, a higher PI value denotes better indoor environmental conditions for the conservation of the exhibition. The abovementioned postprocessed data were used to verify if the climate had undergone any change and, in such a case, to what extent, to evaluate the suitability to preserve artworks and collection objects in non-air-conditioned buildings and which buildings characteristics mostly support this solution. The results obtained in the two case study buildings are discussed and compared. The analysis is carried out according to the main Italian reference standards D.M. 10.05.2001 [16] and UNI 10829:1999 [15]. The applicability of the latter, however, has been questioned in the existing literature [42]. Therefore, the data were also analyzed according to the standard UNI EN 15757:2010 [17], which applies a different approach based on methodological indications derived from the scrupulous analysis of the conservation environment [42]. As for the conservation, optimal microclimate parameters can be defined both by the curators and by technical documents and standards. These optimal values should be defined on the basis of the climate history of the exhibits and their materials and structural characteristics. Table 5 lists the reference values recommended by the Italian D.M. 10.05.2001 [16] for the conservation of the category of objects exhibited in the Vasari Corridor, i.e., \"paintings on canvas, oil paints on canvas\", and in the analyzed two rooms of La Specola museum, i.e., \"organic material in general\", as concerns absolute values (T and RH) and daily gradients (\(\Delta\)T\({}_{24}\) and \(\Delta\)RH\({}_{24}\)) of temperature and relative humidity. Figure 7: (**a**) Pictures of the dataloggers in room X and (**b**) room XXII. Moreover, it should be considered that, in accordance with the standard UNI EN 15757:2010 [17], for the conservation of artworks or exhibits involving hygroscopic materials, their historical climate should be prioritized. Indeed, the climate adaptation of the object to the temperature and relative humidity conditions, often for a long time (centuries), must take into account the storage history and the response of the object into the historical microclimate. UNI EN 15757 [17] recommends the historical climate to be maintained, especially as far as relative humidity is concerned, if the object has been found to be stable. In accordance, consistent values should be used as targets when controlling the microclimate conditions in the zone where these objects are conserved through HVAC systems or other strategies. Thanks to the microclimate monitoring for at least 1 year in both buildings, it was possible to define the historical climate for both museums, as detailed in Section 3, and use it to propose energy efficient control strategies for the indoor environment when minimizing the use of HVAC systems. These strategies are proposed as alternatives if non-air-conditioned buildings emerge as unsuitable for the proper conservation of exhibits. Indeed, since this approach allows taking into account the storage history and the response of the hygroscopic objects to the historical microclimate, the range of acceptable indoor microclimate conditions for the preservation can be potentially widened.