## 3 Results and Discussion
### Comparison between Vasari Corridor and La Specola
For La Specola, the following can be observed:  
* Room XXII (internal room, no external walls, with skylight): the average temperature difference is equal to 5.2 \({}^{\circ}\)C and decreases in the warm season (from April to September), while it shows peak values in the coldest months (January, February, and December). Indeed, the innermost position allows a notable buffering from the external cold climate, but provides less protection from summer radiation coming from the skylight and low chances of air exchange in the hottest months. The lowest values of temperature difference occur in late spring/mid-autumn, demonstrating that the effects of solar radiation coming from the unshielded skylight significantly influence the internal temperature. * Room X (corner room with two external walls): the average temperature difference is equal to 3.2 \({}^{\circ}\)C and has almost flat trend from November to June, with values below the  
Figure 28: Trend of monthly temperature difference between indoor and outdoor for the analyzed zones of Vasari Corridor and La Specola museum. average, when the indoor temperature follows more closely the trend of the external temperature. On the contrary, the difference tends to increase and remain almost constant in the hottest months from July to October, when the room is shaded from the outdoor conditions (mainly solar radiation) even more than room XXII, because of the shielded windows. The effects of incoming solar radiation are also relevant in the Vasari Corridor. In particular, the following can be observed:  
* Lungarno--position A (small windows and southern orientation): the average temperature difference is equal to 2.8 \({}^{\circ}\)C and the trend is quite flat, probably due to the protection of the nearby buildings on the north side, except for a slight increase in September and October. * Ponte Vecchio--position B (large windows and east-west orientation): the average temperature difference is equal to 2.9 \({}^{\circ}\)C, but its trend is in contrast with the previous zone. Indeed, starting from April, it increases until September and then decreases, reaching the lowest values, compared to all the zones in both buildings, in the coldest months (January, February, and December) to less than 1 \({}^{\circ}\)C.  
Overall, the discrepancy in the trend of the temperature difference occurs between May and August, i.e., in the hottest months (end of spring-summer), with Lungarno being more exposed to the dominant solar radiation (south orientation). Lastly, in general, it can be noted that, with the exception of room XXII in La Specola museum, in the other analyzed zones, the difference in average monthly temperatures is maintained around 3 \({}^{\circ}\)C. Accordingly, the passive performance of the building envelope is lower than what is required to ensure the indoor microclimate conditions able to preserve the exhibits without the operation of a HVAC system. Therefore, the improvement of the energy performance of the actual building envelope, e.g., higher thermal insulation and solar shading, could enhance the hygro-thermal behavior of the building. However, historical buildings, such as those analyzed in this study, have strict architectural and preservation constraints, which often limit the feasibility of sensitive physical retrofits [43]. This study proposes an alternative strategy to minimize the energy consumed for the operation of the HVAC system, while ensuring the preservation of the exhibits; it is proposed to use the hygrothermal parameters (air temperature and relative humidity) that characterize the historical climate in each museum zone to control the operation of HVAC system in the zone. The historical climate, indeed, provides more flexible ranges than the reference values according to standards for the conservation of cultural heritage [15; 16], thus reducing the energy needs for the environmental control.