More information on the CEN standards
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Common definitions and symbols
Many of the standards were not developed from scratch, and each standard was prepared by a group of experts organised within one of the CEN Technical Committees, each with their specific background and expertise (building, heating, ventilation, lighting, etcetera).
This was also reflected in the terminology, which was not necessarily the same in all CEN Technical Committees and which could easily lead to a Babel-like confusion. The figure shows, as example, a number of terms that were found to be used for energy need and energy use, without a clear picture whether these terms had the same or a different meaning.

Figure: Tower of Babel or towards common definitions?!
Definitions
Consequently, one of the important actions was the preparation of a set of common definitions on the main concepts and physical quantities. Due to the limited time available to develop the standards the preparation of common definitions was carried out in parallel with and even partly after the drafting of the standards. The coordinating task force, CEN/BT TF 173 (currently called CEN/BT TC 371) was responsible for this action. The action focussed on harmonization of terms used in the top level standards.
Symbols
The CEN standards to support the EPBD introduce a large number of quantities and their associated symbols. To facilitate the use of the standards, a common set of symbols and subscripts have been defined.
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Spotlight on three of the top level
The following three standards play a central role in the set of CEN standards to support the EPBD:
EN 15217: “Energy performance of buildings — Methods for expressing energy performance and for energy certification of buildings”
This is the standard that clarifies the different possible approaches for certification.
EN 15603: "Energy performance of buildings - Overall energy use and definition of ratings"
This standard specifies a general framework for:
the assessment of overall energy use of a building;
the calculation of overall energy ratings (primary energy, CO2 emissions, energy costs).
EN ISO 13790 "Thermal performance of buildings - Calculation of energy use for space heating and cooling"
The EPBD explicitly states that the European Commission intends further to develop standards such as EN ISO 13790, also including consideration of air-conditioning systems and lighting.
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List of CEN standards to support the EPBD
The standards are arranged by hierarchy, in accordance with annex A of CEN/TR 15615 (the "Umbrella Document"). A list of the standards including a introduction describes the role of the standards in each section and is based on CEN/TR 15615 (the "Umbrella Document") can be found here:
List of CEN standards to support the EPBD