Application of the cost optimal methodology to two European case studies: an Italian and a Turkish retrofitted existing office buildings

All new buildings will be nearly zero-energy buildings (nZEB) in Europe by the end of 2020, in compliance with the recast Directive on the Building Energy Performance (EPBD recast 2010/31/EU). Thereby changes to the energy performance requirements for buildings are also expected to come through the application of costoptimality concept. The European Parliament and the Council have hence established that Member States (MS) have to create a set of reference buildings to which apply energy efficiency measures and to calculate the cost optimal levels of minimum energy performance. In particular the cost optimal level is defined as the energy performance level which leads to the lowest cost during the estimated economic lifecycle. It must be calculated in accordance with a comparative methodology framework that is based on the global cost method. This one considers, for each energy efficiency measure, the initial investment, the sum of the annual costs for every year (including energy costs) and the final value, all with reference to the starting year of the calculation period. The analysis carried on within this research, apply the comparative methodology framework to two European case studies in order to compare the obtainable results and point out the criticalities of this procedure. In particular two reference existing buildings, now mainly used for office purpose, were selected as the EPBD recast requires applying the cost-optimal procedures by using typical buildings; one of them is representative of the Italian existing buildings stock and the other one of the Turkish one. Although Turkey is not yet a European Member State, but just a candidate, the cost optimal methodology has been applied to a Turkish case study as this methodology represents a current and widespread area of research also in this country. A set of energy efficiency measures has been selected, organized into packages and applied to retrofit the reference buildings. They mostly consist of the improvement of the envelope thermal insulation and of the systems efficiency; the measures have been defined in compliance with the respective national regulations in terms of energy. The on-site production of renewable energy, from PV system on the building roof (when suitable according to the law), has been considered as an additional efficiency measure. The office buildings energy performance and the impact of the efficiency measures have been assessed by means of dynamic simulation with the EnergyPlus code. In order to establish which of the packages defined has the lowest global cost and represents thus the cost optimal level, the global cost method has been applied to the two reference buildings according to the European Standard EN 15459:2007. The global cost calculations result in a net present value of costs incurred during a defined calculation period, taking into account the residual values of components with longer lifetimes. Finally, a comparison of the results achieved in the analyses in the two different European countries has been developed