# Passive Solar Solutions for Buildings: Criteria and Guidelines for a Synergistic Design
## 3 Performance Evaluation of Passive Solar Systems  
### General Investigation  
As the first investigation, a preliminary quantification of the impact of different parameters on the three classes of passive solar systems has been carried out through a set of simulations. The energy analysis has been carried out with the EnergyPlus(tm) simulation tool developed by US DoE. In order to properly compare the outputs, the simulations considered a standard application of different strategies: the same construction and structures have been used, with no specific optimization for different solutions. The simulations have been run during the winter period to evaluate the impact of the solar strategies on the building's heating demand. Two kinds of buildings, an office complex and an apartment building, have been analyzed with different surface to volume ratio, 0.4 and 0.6, respectively, and different heating demand schedules: from 8.00 am to 7.00 pm on the weekdays and turned off in weekends for the office, while the opposite was set for the residential building. Another difference between residential and office building simulation occurred in schedule and magnitude of internal gains such as from equipment and appliances. Simulations have been set at Rome, 41\({}^{\circ}\) 50\({}^{\prime}\), and Frankfurt, 50\({}^{\circ}\) 06\({}^{\prime}\), to evaluate the incidence of latitude. The three strategies, a direct system, a ventilated Trombe wall, and a sunspace, have been simulated both with a north-south building axis and at 90\({}^{\circ}\) rotation (r), with east-west building axis. Both the models contained common building constructions with an external wall U-value of 0.40 W/m\({}^{2}\)K. Base number and dimensions of the windows were set to comply with the minimum window-to-floor surface ratio of 1/8 required by Italian legislation: fenestration constructions have a U value of 1.76 W/m\({}^{2}\)K and a \(g\) of 0.56. With these settings and no passive systems installed, a benchmark value of energy demand of both office and residential buildings has been evaluated as a reference for energy saving of the passive solar strategies. The reference values for Rome and Frankfurt houses are 160 and 290 kWh/m\({}^{2}\), respectively, while office building reference demand is 98 kWh/m\({}^{2}\) in Rome and 112 kWh/m\({}^{2}\) in Frankfurt.  
Implementing the direct system, a wide glazed surface has been added on the south-faced wall or divided between the east and the west facade in the rotated case. Window extension was set at 15% of the floor, according to the common rule of thumb [29]: fenestration U-value and \(g\) are 1.06 W/m\({}^{2}\)K and 0.6, respectively, while a 10 cm concrete slab provides the ground floor construction with a heat storage mass. This simulation is the only one with a specific low emission window kind, as direct systems installed are part of the thermal zone and directly affect building energy balance. Regarding the indirect and isolated systems, they belong to a different thermal zone, which are not considered in building energy balance. In the indirect system simulation, the Trombe wall area accounted for 0.2 m\({}^{2}\) per m\({}^{2}\) of floor area, with an air cavity thickness of 15 cm. The thickness of the external wall, 30 cm, already provided a good buffering of the heat wave. In this simulation, the same clear glass construction of other windows has been applied to the glazed face of the Trombe wall. Finally, the sunspace modelled in the isolated system was designed as a sunporch linked to the main building through a patio door: its envelope was glazed with the ordinary kind of window, except for the floor, which had the same construction as the indoor floor.