ABSTRACT
One of the key aspects of the European Building Performance Directives (EPBD) of 2002 and 2010 was the definition of the obligation to issue building energy certificates for the majority of existing and all to-be-constructed buildings. EU-member states were required to reflect this obligation into their national legal frameworks and derivative guidelines. Thereby, the primary intentions were to: i. define calculation rules for certain key energy and thermal performance indicators (KPI) for buildings (in Austria a normative monthly method was formulated to derive buildings’ heating demand (HWB) and related indicators); ii. facilitate an easy-to-understand comparison between different buildings for tenants and owners via ranking of such KPIs (illustrated as energy-performance-class figures); iii. provide clear and well-defined evaluation schemes for minimum requirements of the thermal quality of buildings and for public subsidy schemes (for instance grants for realizing efficient retrofit strategies). However, since the legal implementation of energy certificates in Austria several problems have emerged: First, the calculation guidelines and corresponding standards changed several times, including a change in the heating-demand threshold values underlying different KPI classes. This renders comparison between energy certificates issued in different years difficult. Furthermore, guidelines entail a number of vague formulations and miss some relevant definitions. Thus, Issuers of energy certificates “enjoy” a high degree of interpretative freedom, as the resulting energy certificates do not necessarily reveal the underlying assumptions. This obviously renders the targeted comparability of buildings rather difficult. Moreover, the expected quality assurance regarding thermal building performance levels cannot be satisfactorily achieved given such uncertainties. This contribution reports on recent efforts and progress of an ongoing research project (EDEN), which addresses the above issues. The project aims to define rigorous procedures for comprehensive documentation of input data used in energy certificates. The primary objective is to achieve, thus, more transparent and reproducible energy certificates. The paper documents the major steps involved in the implementation of the project as follows: i. Identification of uncertainties concerning the data derived from buildings’ geometry and topological circumstances (e.g., neighboring buildings, surrounding obstructions); ii. Identification of uncertainties concerning physical attributes of the buildings’ envelope as well as other input assumptions concerning building usage and operation; iii. Extensive test series (and comparative outcome analyses) with professional and semi-professional participants, who were requested to independently perform energy certificate calculations for the same set of buildings; iv. Sensitivity analysis based on comprehensive test series to identify and document input assumptions with high and low impact on the values of the final KPIs.
