International Conference on Renewable Energies and Power Quality (ICREPQ’13) Bilbao (Spain), 20 th to 22 th March, 2013 Renewable Energy and Power Quality Journal (RE&PQJ) ISSN 2172-038 X, No.11, March 2013 Design standards for residential N-ZEBs in mild Mediterranean climate G. Caruso 1 , G. Evola 1 , G. Margani 2 and L. Marletta 1 1 Department of Industrial Engineering, University of Catania Viale Andrea Doria, 6 - 95125 Catania (Italy) Phone/Fax number: +39 095 7382453, e-mail: gevola@unict.it 2 Department of Architecture, University of Catania Via Santa Sofia, 64 - 95123 Catania (Italy) Phone/Fax number: +39 095 7382509, e-mail: gmargani@darc.unict.it Abstract. In this paper the authors intend to investigate into the possibility of obtaining the Net Zero Energy Building (N- ZEB) standard for a residential building type widespread in Mediterranean climate. To this aim, the study considers a terraced-house apartment building with an external envelope made of clay blocks and concrete structure, which is a very common solution in Italy. At first, the building is thought to be designed according to the current national regulations concerning the insulation level of the envelope; for such configuration, the current energy needs for heating, air- conditioning, lighting and hot water production are calculated through dynamic simulations tools. Then, the study discusses the interventions, both on the envelope and on the energy systems, needed to transform this conventional building into an N-ZEB, avoiding excessive modifications to its design. Due to the diffusion of this typology, the case considered in the paper is very representative, and the conclusions might be extended to a significant portion of the building real estate. The final aim is to define a construction standard that might become a reference for the design of future residential N-ZEBs in Mediterranean countries. Key words Net Zero Energy Buildings, Mediterranean climate, hollow clay bricks, terraced houses. 1. Introduction The European Directive 31 [1] requires in Article 9 that Member States shall ensure that all new buildings are nearly ZEBs by 31 December 2020; furthermore, by 31 December 2018 the new buildings occupied or owned by public authorities should also be nearly ZEBs. The Member States are also required to create national energy plans with the aim, among others, of increasing the number of near ZEBs and defining this concept in practice. Furthermore, Article 2 of the previously mentioned Directive provides the definition of a “nearly zero-energy building”: this is a building that has a very high energy performance, and where the very low amount of energy required should be covered to a very significant extent by renewable sources produced on-site or nearby. According to the Directive, only the energy needs for ambient heating and cooling, hot water production, ventilation and lighting must be taken into account when determining the building energy consumption. A recent study, published in 2010, reports that in the last 20 years around 280 projects with the claim of a net zero energy balance have been realized all over the world [2]. To date, most finished Net ZEBs have been built in northern European countries (Germany and Austria, mainly), USA and Canada. However, a relevant activity in this field is also registered in France, where 18 projects have been already either presented or realized, as described in Ref. [3]. Here, the authors emphasize that the actual energy needs of a very low-consumption building can be far higher than the values predicted in the design stage, because of the unpredictable and usually inappropriate behavior of the occupants. Some interesting indications can also be drawn from the project carried out in Portugal [4], where the impact of passive cooling through natural ventilation is discussed, as well as the role of an “intelligent” façade. In Germany, an estate containing 59 terraced houses was realized in Freiburg [5]. The houses were designed in compliance with the Passivhaus standard, and the low energy consumption was balanced by the photovoltaic yield from the roofs. Not all the apartments satisfied the N-ZEB conditions, but the whole settlement actually did. Other studies focused on the Italian context are reported in Ref. [6] and [7]. However, most examples of N-ZEBs discussed in the literature are tertiary buildings, while only few residential buildings are considered. Furthermore, not many studies refer to mild Mediterranean countries, where usually the energy needs for ambient cooling overcome those for ambient heating; this determines a profoundly different approach to the design of an N-ZEB, not oriented only on the increase of the insulation level. For these reasons, the study presented in this paper applies to residential buildings. The site here considered is placed in Southern Italy, with mild and short heating seasons and relatively hot and long cooling seasons; the main weather data for the site are shown in Fig. 1.