# Passive Solar Solutions for Buildings: Criteria and Guidelines for a Synergistic Design
## 5 Discussion  
As exposed in the paper, the interest on the promotion of passive solar system solutions is relevant to reduce the energy impact of civil/residential structures. Other studies investigated the impact of specific variables: [PERSON] et al. (2016) developed a mathematical model to estimate the indoor temperature trend in a building with a combined passive solar system made of a direct and an unventilated Trombe wall. Their results show that an 80\({}^{\circ}\) rotation of the room with a combined indirect passive system installed leads to indoor air temperatures about 40% lower than the temperatures in the south-oriented room. Results of [PERSON] et al. (2016) on shape factor influence indicate that the rectangular shape provides the higher thermal comfort, while window-to wall-ratio influence on thermal comfort is around 20-55%. Investigations on specific passive solar solutions report results close to the ones showed in this paper. As showed by [PERSON] et al. (2016) the installation of a sunspace can lead to a 10-15% energy saving with no optimization: if a storage tank is added, the reduction can reach from at least 37% up to 87%. Other optimized studies show energy saving percentage even higher than the present paper's data: the integration of a south-faced sunporch in China led to a coal saving rate of 51.9% ([PERSON] et al., 2017), while a Trombe wall-related saving on a residential building in Portugal was about 43% ([PERSON] et al., 2017). The difference in this case could both be due to the very low energy demand of the building, 14.95 kWh/m\({}^{2}\), and the lower indoor comfort temperature setpoint, 18 \({}^{\circ}\)C. Nevertheless, one of the major limits of the investigations on passive solar systems is the generalization of the results. Comparison of performance and savings from different research must take into account the boundary conditions of the passive strategies, such as latitude or kinds of building, which can hugely vary the impact on the total building energy demand. Due to the high  
Figure 11: (**a**) energy demand of the office module and (**b**) energy saving of a 10- and 32-modules office building for different strategies. number of variables defining the interaction of a building and a passive solar system, results from a specific case study or measurement from experimental activity cannot be generalized without proper assumptions. In addition, differently from common building systems, passive solutions deal with the building design at an architectural level to reach the high integration required, thus the sizing process and the optimization strategy of each solution must be tailored to the specific building. Thus, the main purpose of passive solar investigation should be to develop a general framework and guidelines for building design, or a protocol for the optimization process, as tools that can be adapted to different cases. The sizing and design of a passive solar solution is not always simple. Moreover, the efficiency is related to multiple interconnected parameters, both on a technical and a climatic side, thus the evaluation and optimization of passive solar strategies needs to be carried out taking into accounts the different contribution of these factors to various elements: the energy balance, the cost of construction and maintenance, and the environmental impact. Another limit of passive solar analysis is proper technical and economic evaluation, usually based on a pure energy performance evaluation. As the synergy of intrinsic and extrinsic parameters defines the performance of passive solar solution, and the synergy of different systems can guarantee higher levels of energy savings as showed in the previous analysis, a synergy of evaluating factors determine the cost-benefit correlation to optimize this combination. Another element that can be considered in the analysis is the economic impact of the passive solar system, which is sometimes highly relevant.