nZEB: nearly Zero Energy Building in the European Union is a vague concept defined by the Energy Performance of Buildings Directive 2010/31/EU (EPBD). It requires all new buildings from 2021 to meet the nZEB thresholds and ranges and is currently being translated across European countries to local conditions in different ways. The EU is a collection of regions of diverse climates, building cultures, and ways of living, therefore it is impossible to impose a universal model limiting the use of energy in buildings. On one hand, it makes the concept vague, and on the other, it puts a lot of trust in local legislation and knowledge.
Portugal has a privileged climatic condition, with mild winters and warm summers, and prolonged heat waves (primarily in Alentejo), which imply a relatively low energy consumption for heating. At the same time, most of the population inhabits the coastal areas which bring a refreshing breeze in the hottest months. Such advantageous geographic characteristics should be seen as an asset in defining a transparent and ambitious model of nZEB. Hereby we are going to present some observations on how Portuguese nZEB regulations could be updated to include embodied energy, life cycle assessment and on-site energy production. We believe that a better scheme could be achieved — one that contributes to the electrical grid.
The life cycle of a building should be divided into four parts: (A) sourcing and production, construction and assembly, (B) operation, and disassembly, and (D) demolition. A robust nZEB model should include energy consumption limits for each stage of a building lifecycle. Studies on energy use in buildings estimate that the most energy-consuming stage is (B) operation. No doubt, it is typically the longest. Design for full Life Cycle energy-efficiency is a relatively new topic.
Sourcing and production, the first stage of a building’s life cycle, are directly related to the materials and industrial processes used to build, for instance, a beam or a window. It also includes the energy needed for transportation of any building component from the manufacturer to the construction site.
The construction itself is a relatively short process taking into consideration the lifespan of a building. It typically takes from half a year, for a small investment, up to 5–10 years for a large scale public project. Therefore, the energy consumed during the construction process is relatively marginal, some studies  show that it is less than 1% of the total.
Recent studies  in the United Kingdom showed that up to 85% of energy is consumed while operating, mostly for heating, cooling and ventilation. In Portugal this number is typically lower, reaching 10–15% , although some studies show it could be relatively lower . At the same time, energy-efficient building solutions are more popular in northern Europe, such as Passive Housing, which might reduce the operation to 60% of the total life cycle energy use . This solution, however, requires more energy for the other phases. A relatively larger amount of energy is thus embodied in sourcing and production of the materials, than in traditional constructions. Further activities looking for an energy-efficient building must include embodied energy, and the environmental impact of production and installation of complex HVAC systems, materials used for shell, core and interiors.
Additionally, following the New Circular Economy Strategy of the EU, all endeavours must look for solutions according to the closed-loop cycle. Therefore energy needed for disassembly, deconstruction or repurposing of building elements must be taken into consideration while evaluating energy consumption in the building life-cycle.
The European Green Deal and Renovation Wave directives pay a lot of attention to the issue of energy-efficient buildings within the energy transformation. For regulations to be effective in helping solve the long-term climate problem, they must not only be feasible and consider specific local conditions, but they must also include a robust vision of the energy implications of buildings throughout their whole existence.
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