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The international cooperation project IEA SHC Task 40 / ECBCS Annex 52 “Towards Net Zero Energy Solar Buildings”, attempts to develop a common understanding and to set up the basis for an international definition framework of Net Zero Energy Buildings (Net ZEBs). The understanding of such buildings and how the Net ZEB status should be calculated differs in most countries. This paper presents an overview of Net ZEBs energy calculation methodologies proposed by organisations representing eight different countries: Austria, Canada, Denmark, Germany, Italy, Norway, Switzerland and the USA. The different parameters used in the calculations are discussed and the various renewable supply options considered in the methodologies are summarised graphically. Thus, the paper helps to understand different existing approaches to calculate energy balance in Net ZEBs, highlights the importance of variables selection and identify possible renewable energy supply options which may be considered in calculations. Finally, the gap between the methodology proposed by each organisation and their respective national building code is assessed; providing an overview of the possible changes building codes will need to undergo in the coming years.

The idea of a Net Zero Energy Building (Net ZEB) is understood conceptually, as it is understood that the way a Net ZEB is defined affects significantly the way it is designed in order to achieve the goal. However, little agreement exists on a common definition; the term is used commercially without a clear understanding and countries are enacting policies and national targets based on the concept without a clear definition in place. This paper presents a harmonised framework for describing the relevant characteristics of Net ZEBs in a series of criteria. Evaluation of the criteria and selection of the related options becomes a methodology for elaborating sound Net ZEB definitions in a formal, systematic and comprehensive way, creating the basis for legislations and action plans to effectively achieve the political targets. The common denominator for the different possible Net ZEB definitions in the harmonised framework is the balance between delivered and feed-in energy and associated credits. Additionally, other indicators than the mere balance over a period of time may be given in order to add qualified information on the overall “goodness of design” of a Net ZEB. Finally, the monitoring procedure is considered as an integral part of the definition. The idea of a Net Zero Energy Building (Net ZEB) is understood conceptually, as it is understood that the way a Net ZEB is defined affects significantly the way it is designed in order to achieve the goal. However, little agreement exists on a common definition; the term is used commercially without a clear understanding and countries are enacting policies and national targets based on the concept without a clear definition in place. This paper presents a harmonised framework for describing the relevant characteristics of Net ZEBs in a series of criteria. Evaluation of the criteria and selection of the related options becomes a methodology for elaborating sound Net ZEB definitions in a formal, systematic and comprehensive way, creating the basis for legislations and action plans to effectively achieve the political targets. The common denominator for the different possible Net ZEB definitions in the harmonised framework is the balance between delivered and feed-in energy and associated credits. Additionally, other indicators than the mere balance over a period of time may be given in order to add qualified information on the overall “goodness of design” of a Net ZEB. Finally, the monitoring procedure is considered as an integral part of the definition.