## 2 Materials and Methods
### Building Simulations  
The experimental analysis and the estimation of the optical properties of the aerogel layer provided reliable data, which were used as input for building energy analyses. Energy performance was compared to that of conventional glazing solutions, in order to evaluate the potential spread of these solutions in the fenestration market.  
An office building was investigated (Figure 3): the overall dimensions are 80x20x9 m\({}^{3}\) and it is placed so that the large strip windows are present in the east and west walls. Two window-to-wall ratio (WWR) were considered: 50% (WWR1, Figure 3a), a realistic hypothesis, and 100% (WWR2, Figure 3b), which is a limit case representative of the worst conditions in buildings with glass facades; in future works other case studies could be simulated, taking into account also the influence of the frames. The main features of the opaque components of the building envelope are summarized in Table 1. The internal loads (people, lighting, and equipment) are reported in Table 2. The heating and cooling system operating periods were set according to the climate zone, considering an indoor air temperature of 20 \({}^{\circ}\)C and 26 \({}^{\circ}\)C, respectively. The office occupancy was set from 8 am till 6 pm, five days a week. The illuminance project value for office work plane was considered equal to 500 lux, in compliance with EN 12464-1:2011 (Offices, Visual task 5.26.2 Writing, typing, reading, data processing) [25]. The reference Standard EN 12464-1:2011 specifies the recommended values for the illuminance in the workplaces for different building activities and visual tasks. In particular, the mean values of the illuminances are given, together with the Unified Glare Rating (UGR), the Uniformity Index (U\({}_{0}\)), and the Color Rendering Index (R\({}_{\text{a}}\)).  
The 2 nd floor of the building was chosen for the study, so that just the facades are exposed to the external environment conditions (weather, sun, wind, etc.), whereas the floor and the ceiling exchange heat with the adjacent areas at the same temperature. In this way, the ground and the roof temperatures have no effect on the studied zone performance.  
The impact of the new solutions on the building energy performance was simulated through EnergyPlus(tm) 8.4, over a time interval of 1 year, with data points gathered every hour and taking into account different climatic conditions: Rome (Italy), characterized by a hot climate, Paris (France) and Turin (Italy), with a moderate climate, and Helsinki (Finland) with a cold climate. In order to optimize the facade configuration, a comprehensive approach was used and the heating, cooling, and artificial lighting energy demands were calculated [26; 27]. A screen was considered as external shading device (solar transmittance equal to 0.1, light transmittance equal to 0.15), for reducing the cooling loads due to the large windows in the east and west walls. The optimal setting was investigated by means of preliminary simulations: the shade is automatically activated when the indoor air temperature is higher than 22 \({}^{\circ}\)C during the cooling period.  
All the glazing units (the innovative and the conventional ones) were modelled as multiple layer windows by means of Berkeley Lab WINDOW 7.4 program [28]. Data from the Library were used for conventional glazing and the layer optical properties (transmittance and reflectance) were considered as a function of wavelength. The glazing with monolithic aerogel was modelled as a triple glazing (in which the middle layer is the aerogel pane), by using the Berkeley LabOptics 5.0 tool [29]. As spectral optical properties of the glass layers were assumed data from the experimental campaign, whereas data estimated according to the procedure described in paragraph 2.3 were used as input spectral optical data for the monolithic pane [17].  
Figure 3: Model of the buildings: Window-to-Wall Ratio (WWR1) (**a**) and WWR2 (**b**).