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With the current movement towards Net Zero Energy Buildings (Net ZEBs) decisions regarding energy carrier weighting factors will have implications on which technologies could be favoured or disfavoured, and therefore adopted or not adopted, in the building sector of the near future. These implications should be taken into consideration by policy makers when developing legislation and regulations addressing the building sector. A parametric analysis was conducted on six buildings in Europe of different typologies and climates in order to assess how different weighting factors would impact the choice of technical systems to be installed. For each combination the amount of PV capacity necessary to achieve a net zero balance has been calculated and used as the main indicator for comparison; where less PV area means more favourable condition. The effect of including a solar thermal system is also discussed. With the current European national weighting factors, biomass boiler is largely the preferred solution, frequently achieving the balance with PV installed on the roof, while gas boiler is the most penalized. The situation changes when strategic weighting factors are applied. Lower weighting factors for electricity and district heating, e.g. reflecting national targets of increased penetration of renewables in such grids, would promote the use of heat pump and district heating, respectively. Asymmetric factors aimed at rewarding electricity export to the grid would facilitate the achievement of the zero balance for all technologies, promoting cogeneration in some cases. On the contrary, low weighting factors for electricity, e.g. reflecting a scenario of high decarbonisation of the power system, prove quite demanding; only few technical solutions would be able to reach the balance within the available roof area for PV, because of the low value credited to exported electricity. In this situation, the preferred solution would be heat pumps combined with solar thermal. In addition, the choice of weighting factors and the resulting favoured technologies will determine the temporal matching of load and generation. While all-electric solutions tend to use the grid as seasonal storage, other solutions will have a yearly net export of electricity to the grid to compensate for the supply of other (thermal) energy carriers. Therefore, it is important to consider the implications for the electricity grid resulting from the choice of weighting factors.
The concept of Zero Energy Building (ZEB) has gained wide international attention during last few years and is now seen as the future target for the design of buildings. However, before being fully implemented in the national building codes and international standards, the ZEB concept requires clear and consistent definition and a commonly agreed energy calculation methodology. The most important issues that should be given special attention before developing anewZEB definition are: (1) the metric of the balance, (2) the balancing period, (3) the type of energy use included in the balance, (4) the type of energy balance, (5) the accepted renewable energy supply options, (6) the connection to the energy infrastructure and (7) the requirements for the energy efficiency, the indoor climate and in case of gird connected ZEB for the building–grid interaction. This paper focuses on the review of the most of the existing ZEB definitions and the various approaches towards possible ZEB calculation methodologies. It presents and discusses possible answers to the abovementioned issues in order to facilitate the development of a consistent ZEB definition and a robust energy calculation methodology.
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). Th e 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.