Passive House & Nearly Zero Energy Buildings

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. Energy inefficiency will occur when the dwelling fabric including the walls, roof, floors and junctions are affected by poor detailing and insulation standards, resulting in energy losses and, with that, increased costs for domestic bills.

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. Active policy measures aiming to improve buildings’ energy performance, supported by an increased use of low energy and renewable technologies would be extremely beneficial under multiple perspectives. 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.

European legislative framework

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.

Near Zero Energy Buildings (NZEB)

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 31 December 2018 new buildings occupied and owned by public authorities must meet the nearly zero-energy standard (Art. 9.1 (b)); by 31 December 2020 all new buildings must meet the nearly zero- energy standard (Art. 9.1(a)).

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, while taking into account: (a) the Member State’s detailed application in practice of the definition of nearly zero-energy buildings, reflecting their national, regional or local conditions, and including a numerical indicator of primary energy use expressed in kWh/m² per year. Primary energy ‘factors’ used for the determination of the primary energy use may be based on national or regional yearly average values and may take into account relevant European standards; (b) intermediate targets for improving the energy performance of new buildings, by 2015, (c) information on the policies and financial or other measures adopted in the context of for the promotion of nearly zero-energy buildings.

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.

General Definition

The Energy Performance of Buildings Directive defines net zero energy buildings, in broad terms, as those buildings with high energy efficiency performance. As stated in the Directive, the nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby.

In other words, 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. The outworking of the legislation is that different countries adopted different approaches and metrics. 

In 2007, in advance of the European Directive, the UK decided to commit to a Zero Carbon Standard by 2016, a commitment that was not achieved. The initial definition of Zero Carbon Homes now differs from the definition of Nearly Zero Energy Buildings. The NZEB definition considers CO2 emissions from regulated energy use only, and results from the combination of carbon compliance measures (Fabric Energy Efficiency Standard & established Carbon Compliance limits) and “allowable solutions” (CO2 off-setting such as investments in carbon reduction projects).

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 Efficiency 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.

In order to transpose NZEB requirements into national legislation, public consultations on the review of Part L (Conservation of Fuel and Energy) of the current Building Regulation have been opened. Mandatory provisions have been made for 20% of the energy load to derive from renewable energy sources. The proposed amendment also advises a substantial reduction of 60% in buildings energy use, compared to the current consumption levels allowed.

Reaching NZEB through the Passive House Standard

Since energy efficiency consists in reduction of consumption and reduction of greenhouse gas emissions, the Passive House standard has emerged as a key enabler for the Nearly Zero Energy Building standard. The combination of PH with renewables represents a suitable solution to move to low/zero carbon. Passive houses, indeed, 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. Whilst 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.