978-1-5386-5186-5/18/$31.00 ©2018 IEEE A general approach for retrofit of existing buildings towards NZEB: the windows retrofit effects on indoor air quality and the use of low temperature district heating Livio De Santoli, Davide Astiaso Garcia, Daniele Groppi Department of Astronautical, Electrical and Energy Engineering University of Rome “Sapienza” Roma, Italy Laura Bellia, Boris I. Palella, Giuseppe Riccio Department of Industrial Engineering University of Neaples “Federico II” Napoli, Italy Gennaro Cuccurullo, Francesca R. d’Ambrosio Department of Industrial Engineering University of Salerno Fisciano (SA), Italy Luca Stabile, Marco Dell’Isola, Giorgio Ficco, Aldo Russi, Gaspare Giovinco Department of Civil and Mechanical Engineering University of Cassino and Southern Lazio Cassino (FR), Italy Andrea Frattolillo Department of Civil and Environmental Engineering and Architecture University of Cagliari Cagliari, Italy … Abstract — The European Union, through the Energy Performance of Building Directive (EPBD), has recently set the minimum requirements in order to reduce the energy consumption of existing buildings and achieving nearly zero energy buildings (NZEBs). In order to comply with these requirements different aspects of the building sector have to be dealt with. In the present paper two different aspects related to the energy and environmental performances of the existing building towards NZEB are analyzed: a) the use of the Smart Energy Systems with particular regard to the heat sharing systems, and b) the effect of the window retrofit on indoor air quality. Keywords — NZEB; retrofit; ventilation; Smart Energy Systems; Heat Pump; IAQ I. INTRODUCTION A key challenge for European Countries, like Italy, characterized by a rich building heritage (mostly identified as Historical Buildings), is the energy retrofit of existing buildings in order to make their energetic performances as close as the NZEB ones. This is even more important for buildings erected after World War Two through novel techniques, characterized by the use of reinforced concrete and prefabricated building components, with respect to the traditional ones. Actually, as the days go by, building quality resulted poor: e.g. the reinforced concrete turned out to be not everlasting, the walls shown major issues in terms of energy performances, the whole building did not result earthquake-proof (this is a main concern in Italy where high standards are required due to its seismic risk [1]). Summarizing, the Italian building heritage should be deeply retrofitted, such retrofit should be synergic as it should take into account simultaneously the different criticalities of the buildings [2]. Despite the priority actions to be carried out in terms of seismic risk, an integrated approach in building retrofitting should be used in the transition towards the NZEBs. This is even more important for building reconstruction in the towns of Central Italy recently hit by a devastating earthquake. Retrofit actions can obviously concern both the building envelope and the HVAC system [3], but not always can be performed contemporarily. In fact, very often existing buildings show several constraints (e.g. historical and/or This research has been carried out within the “Renovation of existing buildings in NZEB vision (nearly Zero Energy Buildings)” Project of National Interest (Progetto di Ricerca di Interesse Nazionale - PRIN) funded by the Italian Ministry of Education, Universities and Research (MIUR).