A design approach for the solar optimization of built volumes: validation on a residential building’s project in a historical district in Milan, Italy

This paper presents a process of solar potential optimization for residential buildings in high density urban areas. The process is validated through its application to the project of a mixed use, net zero energy building including public facilities and four levels of apartments. The optimization process concerns three phases: energy, solar and panelling optimization. The design approach combines parametric volume transformations (Rhinoceros - Grasshopper), solar dynamic analysis (Daysim) and solar maps analysis (DIVA for Rhino). The energy optimization regards the reduction of the heated volume, compared with the allowable volume defined by the regulations of the city of Milan, to a smaller one with lower internal heights, minimizing the building’s energy demand. The solar optimization is focused on the transformation of the initial volume based on the local urban parameters (distance among buildings, allowable profile, building’s height, plot ratio), in order to improve the solar exposure and maximize the solar access. The façades are modified to reduce the overshadowing effect of the nearby buildings, maintaining the same volume. The optimized volume derives from parametric studies about solar availability tilting the vertical facades away from the vertical. Solar dynamic annual analyses were conducted using Daysim and DIVA for Rhino in order to compare the initial and the solar optimized scenarios. The first set of simulations was carried out on both the isolated initial and optimized volumes, while the second set was carried out on the latter volumes placed in the district, thus affected by the surroundings. The loss in floor area due to the slope of the south and east façades is balanced by the addition of living areas facing the inner court without losing any commercial floor area. This choice allows a comparison of the two buildings, which have different shapes but the same volume. The annual solar mapping analysis is performed to localize the most irradiated parts of the building envelope, giving the possibility to design both a photovoltaic or thermal solar system with variable density elements. The results show the increase of available solar radiation in solar optimized design, while the panelling study permitted to optimize both technology and energy design of the solar systems required and furthermore to justify the architectural choices that led the building’s design. The studies have demonstrated that through the optimization of the building shape, it is possible to obtain a huge improvement in the amount of solar radiation available on the façades, while keeping the same envelope surface. The next steps of the research will be focused on the analysis of both photovoltaic and solar thermal panels’ efficiency, as well as the related assessment of increased surface temperatures on the façades, due to the solar energy system integration.