Retrofit strategies towards Net Zero Energy Educational Buildings: a case study at the University of the Basque Country.

Abstract

Educational buildings in Europe account for around 20% of the entire non-residential floor space where good indoor comfort and air quality are essential for correct educational development. Directive 2010/31/UE upholds that the public administration should promote the transformation of its buildings towards Net Zero Energy Buildings. In Spain, it is particularly important to act on the existing building stock since the construction of new buildings has been considerably reduced as a result of the bursting of the property bubble following the frenzied building activity over the last few decades. This paper proposes a method that starts by studying user comfort under real conditions through a questionnaire and monitoring campaign. This analysis revealed that students prefer lower indoor temperatures (20-22-5ºC) than stated by theoretical comfort models. The need for lower temperatures combined with high internal gains mainly due to computers and lighting, constitute the first strategy to reduce the heating needs. The principal measures that make it possible to achieve comfort conditions work together with energy saving strategies, which can be achieved through effective interventions in the buildings: eliminating thermal bridges, using air-to-air heat recovery systems and improving the windows in the north façade of the building. The results show a potential energy saving of up to 62%. Furthermore, overheating problems reported by users in summer and shoulder seasons could be solved by using day and night time natural ventilation, avoiding the installation of air-conditioning systems and all the associated environmental impacts. Finally, acting on the existing building stock implies necessarily understanding user needs in order to define most adequate energy saving strategies.