The effect of roof-integrated solar technologies on the energy performance of public buildings : The case study of the City of Turin (IT)

The City of Turin is a town with about 900.000 inhabitants and is the capital of Turin Metropolitan City and Piedmont Region. It is located in the plain area and is surrounded by the Alps and with a temperate climate. According to Sustainable Energy Action Plan of the Covenant of Majors initiative, Turin owns a public building stock of more than 8% of the entire city, with a significant impact on urban whole energy consumption of about 375,000 MWh/year at 2005. The City of Turin was therefore interested in managing its own energy consumptions and proposing a strategy to improve the energy performance of its building. In this context, the municipality was also interested in the production of energy from renewable sources, in particular with solar technologies for a reduction in GHG emissions. In this work, 71 public buildings owned by the City of Turin were cataloged and classified in 4 categories based on the type of use (48% are schools, 14% schools with swimming pool, 34% offices and 4% sports facilities). Energy consumptions with thermal and electrical energy-use data, were collected for three consecutive years. The analyzed public buildings consume an average of 74,803 MWh/year for space heating and 11,317 MWh/year of electricity and most of the public buildings are connected by natural gas and district heating network; this last is the largest in Italy and one of the largest in Europe. With the digital surface model (DSM) of the City of Turin, a 3D solar irradiation model was elaborated taking into account the monthly characteristics of solar irradiation and of atmosphere transparency in Turin. This model was used to calculate the availability of solar irradiation on the roofs of public buildings, the extent of free roof surfaces and then the potential of energy produced by the current and available solar technologies on the market. Finally, the energy performance of the most used solar technologies was evaluated with a cost/benefit analysis to evaluate future scenarios. A GIS-based project was also created to manage and to update the energy performances of public buildings. The results of this work showed that, for 31 buildings with a high intervention priority installing solar technologies there could be a reduction of 2-7% of space heating and of 5-15% of electricity consumptions. A more rational use of energy to manage energy demand and supply of the overall public buildings stock could be an effective strategy on targeted interventions that, combined with an efficient use of space, lead to take a virtuous path towards the sustainability of the urban environment. Then, the use of a GIS-based assessment is essential to compare the energy demand with the potential of energy produced by roof-integrated renewable energy technologies. The aim of this work is to implement energy policies based on the real buildings heritage but also to increase transparency and awareness of citizens on the effort of public administration to reach environmental sustainability targets.