Energy efﬁciency and the building sector
Commercial and residential buildings in Europe are overall responsible for 40% of total energy consumption and 36% of CO2 emissions. Similar trends are registered in Ireland and Northern Ireland, where the residential sector alone accounts respectively for 27.1% and 30% of the overall energy use, contributing with almost equal percentage of CO2 emissions. Space and water heating, cooling systems, lighting (regulated energy) and appliances (unregulated energy) constitute the main sources of energy consumption in a domestic environment. Considering the relevance of the statistical and practical impact of building energy inefﬁciency, the potential for a renovation of the commercial and residential sectors are easily understandable.
Academic studies show that, in the most ambitious scenario, by 2020 the share of nearly zero energy buildings will reach 6% of the total stock, leading to emission reductions of over 50% compared to the 1990 level and primary energy reductions of 25% compared with today. Securing a more sustainable and energy efﬁcient housing stock implies economic beneﬁts, as a consequence of reduced housing running costs, reduced dependency on fossil fuel and energy import. An energy efﬁcient house has also proved to provide better comfort, health and living standards.
It is in this scenario that the so called “zero energy” or “zero emission” buildings have been identiﬁed as the main solution to convert the building sector into more sustainable and affordable standards. Net Zero Energy Buildings represent now both a legislative requirement and a crucial element of the European and national policy agenda for the building and environmental sector.
In simple terms, a nearly zero energy building is a house which is responsible for little or zero carbon emission. This goal can be reached due to fabric improvements (insulation, airtightness, etc.) and extreme low carbon heat and power technologies (high-efﬁciency boilers, photovoltaic panels, solar hot water, etc). The main instruments supporting the transition to zero carbon are the progressive tightening of national building regulations and the domestic transposition of the EU Directives.
In Ireland, the implementation of NZEB is developed “in the light of cost-optimal calculations, industry consultation, review and public consultation as well as further developments in relation to policy and legislation”. A National Energy Efﬁ ciency Action Plan is in place, as prescribed by the directive on energy performance of buildings and the national regulation is incrementally setting higher standard for buildings energy performance.
Reaching NZEB through the Passive House Standard
Passive houses focus on energy saving instead of energy production, which is also the path paved by European legislation and environmental targets. A passive house is designed to have an energy demand that is as low as practically achievable. With such a small amount of energy to be supplied, it is easier to meet the subsequent demand by renewable sources.
The renewables sector while a vital part of the overall solution, is still affected by some fundamental issues. While it is possible (but potentially costly) to size a renewable energy system to address the energy gap, issues remain such as the seasonal gap. This is the inability to store excess energy generated in the summer (especially that which is produced through solar PV) for use during the winter period when demand for energy is higher. For this reason, the combination of low energy standards such as Passive House, together with renewables, represents the perfect match. It involves fewer costs (reducing the capital and maintenance costs associated with renewables) and solves problems related to energy storage and seasonal gaps.
European legislative framework and NZEB
The United Nations Environment Programme identiﬁed building energy standards as among the most effective instruments for reducing buildings related emissions. The European union has set up a regulatory framework to address and lead buildings energy efﬁciency, with the Energy Performance of Buildings Directive (2010), the Directive on Energy Efﬁciency (2012) and the Renewable Energy Directive (2009) as its key tenets.
The Directives have been recently updated, with the recast Energy Performance of Buildings Directive (EPBD) introducing the concept of Nearly Zero Energy Buildings (NZEB) and specifying that, by 31st December 2018, new buildings occupied and owned by public authorities must meet the nearly zero-energy standard, and that by 31st December 2020, all new buildings must meet the nearly zero- energy standard.
The Directive encourages Member States to draw up national plans for increasing the presence of NZEB on EU territories, designing their own path towards a net zero energy building stock.
However, while laying down the general goals that must be achieved, the Directive provides neither a detailed methodology nor speciﬁc deﬁnitions and putting those criteria into practice is left to Member States’ discretion.