# Passive Solar Solutions for Buildings: Criteria and Guidelines for a Synergistic Design
## 3 Performance Evaluation of Passive Solar Systems
### Analysis of a Case Study  
After a general investigation to quantify the impact of the different variables on the performance of the three kinds of passive solar strategies, another simulation was run to define possible effects of the synergy of different solutions on a case study of a real building. The aim was to provide a quantification of the energy saving that could be obtained with the design of passive solutions in an existing building. The selection of the case study has been influenced by various elements, as the positive effects of passive solar systems can be evaluated referring to both specific civil buildings for residential or public use. Between residential and public buildings, the latter result to be more energy consuming: daily use and commonly wide glazed envelopes make them also the most suitable kind of buildingsfor the implementation of passive solar systems. The European Directive 2010/31/UE [30], in fact, firstly focused its attention on public buildings, anticipating the requirement for nearly zero-energy buildings (nZEB) in new construction. For these reasons, the case study is based on the office building of the Department of Energy, Systems, Territory and Constructions Engineering of the University of Pisa, shown in Figure 6. The building hosts offices and research laboratories on two floors: the technical room for the building system at the ground level and the adjacent building with mechanical laboratories were not included in the simulation. It develops along the south-north axis, and is characterized by a wide glazed envelope, mainly equally east- and west-exposed with a gross window-to-wall ratio of 57.65%. For energy modeling, people, lights, and equipment loads were considered; no mechanical system has been modelled, only natural ventilation to simulate the passive behavior of the building and its energy demand. Table 3 lists the main construction involved and internal gains used. Zone ideal loads have been evaluated with a heating setpoint at 20 \({}^{\circ}\)C and a cooling one at 26 \({}^{\circ}\)C. Natural ventilation through existing windows has been set according to the occupancy pattern and with an outdoor air temperature range between 15 and 30 \({}^{\circ}\)C.  
The first solution investigated shading systems: given the high-glazed surface, this results as the easiest and most cost-efficient kind of passive solar solution. Fixed overhangs and external adjustable blinds, as the ones installed, were both simulated to compare their efficacy. The simulation has been set to activate the blind closing when 500 lux have been reached over the working plan or indoor air temperature rises above 25 \({}^{\circ}\)C, with a tilt angle configured to block direct beam solar radiation. A second passive strategy to reduce heat losses through the glazed envelope, focused on the integration of solar-control low-emissivity glasses. The windows chosen for this simulation had a solar control glass layer replacing common 4 mm clear glass, with a solar transmittance at normal incidence of 0.166: window U value moved from 2.7 to 1.65 W/m\({}^{2}\)K while the solar heat gain coefficient \begin{table}
\begin{tabular}{c c} \hline \hline
**Construction** & **Thermal Conductivity [W/m\({}^{2}\)K]** \\ \hline External brick wall & 1.05 \\ External brickwork & 0.94 \\ External concrete wall & 2.50 \\ Office floor slab & 1.07 \\ Laboratories floor slab & 1.47 \\ Roof & 0.428 \\ \hline
**Load** & **Specific intensity [W/m\({}^{2}\)]** \\ \hline \hline Lights & 7.00 \\ Electric equipment & 5.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Model details. Figure 6: Case study building: (**a**) energy model; (**b**) standard floor plan  
decreased from 0.764 to 0.617. To fully exploit the potential of passive solar strategies, different solutions must be combined and balanced to take advantage of the energy savings coming from each system, as they can act on distinct services and in distinct times: for this reason, a combined solution, with external blinds and low-e glasses, has also been investigated.