Öz The EU Energy Performance of Buildings Directive (EPBD) 2010/31/EU is a step in the right direction to promote near zero energy buildings (NZEB) in a step-wise manner, starting with minimum energy performance and cost optimal thresholds for “reference buildings” (RBs) for each category. Nevertheless, a standard method for defining RBs does not exist, which led to a great divergence between MS in the level of detail used to define RBs for the EPBD cost-optimal analysis. Such lack of harmonisation between MS is further evident given the resulting large discrepancies in energy performance indicators even between countries having similar climate. Furthermore, discrepancies of 30% or higher between measured energy performance and that derived from the EPBD software induces uncertainty in the actual operational savings of measures leading to cost-optimality or NZEB in the simulated environment. This research proposes a robust and innovative framework to better handle uncertainties in the EPBD cost-optimal method both in the building software input parameters and in the global Life Cycle Costings (LCC), making the EPBD more useful for policy makers and ensuring a more harmonised approach among MS. The concept behind the proposed framework is the combination of a stochastic EPBD cost-optimal approach with Bayesian bottom-up calibrated stock-modelling. A new concept of “reference zoning” versus the “reference buildings” approach is also introduced in this research, which aims at providing a simpler and more flexible aggregation of energy performance for the more complex commercial building stock.
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