NetZeroCities

The design and operation of zero or very low energy buildings started in the 2000s and even earlier. The basic idea is to use energy conservation technologies combined with renewable energy systems to decrease as much as possible the energy use of buildings (see Figure 1). Nearly-Zero Energy Buildings (NZEBs) have continuously gained acceptance by the market and the research community and several thousands of such buildings have been built and monitored.

The NZEB principle has been adopted as the current and future policy by the European Union. Indeed, according to the EU Directive on Energy Performance of Buildings (EPBD) [1], new buildings occupied by public authorities had to be NZEBs by December 31, 2018 and all new buildings had to comply by December 31, 2020. NZEBs are defined as buildings with a very high energy performance, as determined in accordance with Annex I of the EPBD. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources produced on-site or nearby. The EPBD does not prescribe a uniform approach for implementing NZEBs. It states that Member States shall detail NZEB definitions, reflecting national, regional or local conditions, and including a numerical indicator of primary energy use expressed in kWh/m2/year. As such, the requirements show heterogeneity across the various Member States [2]. On average, NZEBs energy performance levels appear 10% higher than the benchmark levels recommended by the Commission in 2016 [3] in most Member States.

Most common NZEB technologies include both passive solutions (e.g. sunshade, natural ventilation and lighting, night cooling), and active solutions (e.g. mechanical ventilation with heat recovery, heat pumps in combination with efficient lighting, appliances, and envelope). The typical envelope U-values fall in the ranges 0.15 – 0.20 W/m²K (walls) and 0.10 – 0.25 W/m²K (roofs). Regarding renewable energy sources, PV and solar thermal are frequently used [4].

Numerous building design procedures and principles are employed to achieve the nearly zero energy target resulting in a variety of potential solutions that present significant cost differences. Some favour excessive use of photovoltaics or other renewables and almost an insignificant use of energy conservation technologies, disregarding the primal objective of high energy performance and thus minimal energy needs.

However, the Commission’s proposal to revise the EPBD [5] (December 2021) makes a step forward from current NZEB to zero-emission building (ZEB), aligning the energy performance requirement for new buildings to the longer-term climate neutrality goal and “energy efficiency first principle”. According to the directive’s proposal, a ZEB is defined as a building with a very high energy performance, with the very low amount of energy still required fully covered by energy from renewable sources generated on-site, from renewable energy community or from a district heating and cooling system. The ZEB requirement should apply as of 1 January 2030 to all new buildings, and as of 1 January 2027 to all new buildings occupied or owned by public authorities.

Figure 1. Concept of a NZEB [2]

Both NZEB and ZEB can be autonomous or connected to an energy infrastructure. Most of the existing low or zero energy buildings are connected to the grid.

Various options exist concerning renewable energy supply. Figure 2 presents those applied in international energy calculation methodologies, ordered following the location of the energy supply option with respect to the building.

Figure 2: Overview of possible renewable supply options, [6]

Several concerns about the additional cost induced by zero energy buildings especially for the low income population are expressed. To minimize the cost, several studies exist aiming to investigate the necessary investments to build and run zero energy buildings in Europe, [7,8]. Increasing experience, industrial development on energy conservation and renewable energy technologies and the massive construction of zero energy buildings has resulted in a considerable decrease of the cost of zero energy buildings. However, given the current and future cost of energy and the additional cost induced by global and regional climate change, investments related to zero energy buildings are necessary and justified.

Figure 3: A zero energy Building in Poland

Figure 4: A zero energy office building in Belgium

Figure 5: A zero energy building in Lucia Spain

Figure 6: A zero energy building in the UK

Economy: Job Creation Labour productivity, Better working conditions. A review of the literature shows that for a similar energy output, solar energy creates 55-80 times as many direct jobs as natural gas, energy conservation measures create 26 times as many direct jobs as natural gas at about one-ninth to one-fifth of the cost. At the same time, for a similar energy output, solar heating systems create 2-8 times more direct jobs than conventional power plants. According to the European Green Deal Strategy 160 000 additional green jobs could be created in the construction sector by 2030 (18). In parallel, the potential creation of full time employment, FTE, in the EU countries arising from the transformation of the existing building stock to NZEB is estimated in (19), and given in Figure 7 below. The job positions associated with the total investment costs showed heterogeneity across the European regions, with low values in Austria, Cyprus, Greece, Ireland (Midland and Western), and Sweden. Only six European regions from the 235 (2.5%) showed high values exceeding 1230 FTE.

Figure 7: Absolute value of Full-Time Equivalent (FTE) job positions associated with the total investment costs to transform the existing building stock to NZEB, Source (19)

Economic risks mitigation: Energy security and Safety and Security (Reduced energy poverty, Increased access to clean, affordable, and secure energy): Use of energy conservation and of renewable energies in the built environment helps to improve energy security and safety while contributing to alleviate energy poverty. Unfortunately, no data is currently available on the impact of zero energy buildings on energy poverty. However, the development of zero energy buildings ‘brings many positive effects: (i) improving people’s living conditions, (ii) decarbonising the energy system, (iii) sustaining recovery and growth. These are the main objectives pursued by the recent Renovation Wave, which as the backbone of the EU Green Deal on energy efficiency in buildings, shows a focused orientation on fighting energy poverty. Among the key actions to be taken in 2021, the EU is committed to “tackling energy poverty and worst-performing buildings: launching the Affordable Housing Initiative piloting 100 renovation districts.”5 Renovation and improvements to the energy performance of buildings would also bring multiple indirect effects, such as (i) improvement of health, due to the reduction of air pollution, and consequent reduction of healthcare costs, and (ii) boost economic activity’, (20).

Health: Higher or lower indoor temperatures, caused by inappropriate heating and cooling of buildings, seriously affect human health and heat-related mortality. Energy conservation and renewable energies systems implemented in zero energy buildings, help to keep indoor temperature at the proper levels and protect the health of the tenants, contributes to less premature deaths, increase the life expectancy, decrease the risk of heat related mortality and morbidity and in general reduces the health risk from extreme heat events.

Environment: Environmental risks mitigation: Reduced ecological footprint: The use of energy conservation and renewable energies implemented in zero energy buildings, decreases the use of air conditioning and reduces the production of electricity resulting in less emissions and pollution and a decreased ecological footprint of cities.

Climate resilience: climate adaptation: Reduced risk to natural and climate hazards, heat waves and extreme climatic events

Climate and geography: Zero energy buildings can be implemented under all climatic conditions. Member States have in place definitions reflecting regional or local conditions. The specific design should follow the main energy requirements and should be fitted to the local needs.

Policy and regulatory/legal framework: Zero energy buildings are promoted through a complete and comprehensive policy framework defined by the European Commission and the Member States. The whole legislative frame is described in (21).

Project governance and implementation modalities:

Upstream community work: Most retrofits require an agreement between inhabitants, owners, real estate companies and other stakeholders. Working with the community prior to interventions is critical, including attending to and understanding the demands of the residents both individually and as a community and being able to convey how the improvements in the rehabilitation of the building relate to those demands.
Hierarchize the solutions and prioritize them according to their cost and impact. Adapt solutions to the social context and its economic resources. Establish a sequence of possible interventions according to the budget of the tenants/owners who must implement them.
Get tangible results in the first actions that allow user loyalty and encourage them to continue with the process.
Specify and transmit in a clear and simple way the impact of the proposed solutions in the different areas that affect the citizen: environmental, health, economic, etc.

Funding and financing: Funding and financing of projects on zero energy buildings can be performed using National financing schemes. In most of the European countries appropriate project to rehabilitate private or public buildings to NZEB, are available. The schemes differ substantially between the countries. Cities can also benefit from public-private consortiums to finance the rehabilitation of existing communal buildings to NZEB through third party financing procedures. Additionally, cities take advantage of government tax credits, manufacturer equipment rebates, and utility incentives.

It is important to point out that according to (22): ‘The building renovation rate and depth in Europe need to increase sharply in order to reach the pace of building decarbonisation necessary to reach zero emissions by 2050. Currently, the renovation rate across the EU-28 is 1% per year. The deep renovation rate is much lower, at 0.2-0.3%. According to the European Commission, approximately EUR 125 billion in additional yearly investments in the residential sector are needed to reach the EU’s current 2030 renewable energy and energy efficiency targets. Given there are 215 million residential buildings in the EU, this amounts to an average of EUR 600/year additional yearly investments per building. Optimisation of the design to minimise the cost and maximize the energy benefits is a necessary task to be undertaken by the design teams. In addition, decarbonisation measures in buildings can lead to disruption and hassle for the buildings’ occupants’. According to the Green Deal program of the EU 35 million buildings could be renovated by 2030.

Member States currently can support energy conservation and the use of renewable energies in buildings and communities through programs integrated into their development strategies and co-financed from several European initiatives.

Energy and Environmental Impact: Combining energy efficiency with the deployment of renewables, NZEBs have low to zero net energy consumption.

Wide implementation of zero energy buildings in a city presents several energy related benefits:

Decreases the absolute energy consumption during the whole year at the city scale.
Decreases the release of harmful pollutants from the heating and cooling systems of the buildings.
Decreases the peak electricity demand during the year and the need to build additional power plants.
Decreases the cost of electricity as the absolute peak demand is seriously reduced.
Decreases the release of anthropogenic heat and reduces the magnitude of local overheating.

At the same time, the wide deployment of NZEBs is crucial for the countries in achieving the EU 2030 target of reducing the final energy consumption in buildings by 14% and energy consumption for heating and cooling by 18%. As a result of the energy conservation policy in the building sector, between ‘2000-2019, downward trends are observed for space heating, the dominant end-use with 66% of the household consumption, and cooking (only 5% of the total) (consumption decreases by -0,5/%year and -0.3%/year for space heating and cooking respectively). Over the same period, increasing trends are observed for household appliances (2.5%/year) and water heating (0.2%/year increase in consumption)’. In parallel, the specific consumption of households for heating has decreased in almost all countries since 2000 (- 1.8%/year on average in the EU), and the household energy efficiency has improved by 29% at EU level between 2000 and 2019 (or 1.8%/year) (30).

Provide Comfort: Zero energy buildings provide the best indoor comfort conditions at much lower operational cost.

Examples of proposed indicators to measure the impacts of this solution if applied in a city:

Energy savings compared to reference buildings (% kWh/m2/y). Calculate the energy consumption before the implementation of the global energy system, A, in kWh/m2/y and the corresponding energy consumption when the full energy system is implemented, B. Then calculate the Impact Indicator as E=A-B

GHG emissions avoidance (e.g., by removing the need for energy consumption) in %CO2e. Calculate emissions corresponding to the energy consumption A and B, as above, then calculate the difference.

Educational/ Capacity building

Trainings: Training of energy engineers, urban planners, architects, on the optimum design and implementation of NZEBs. Additionally, training processes for residents so that they can understand the advantages and consequences of the required solutions and make decisions based on concrete knowledge.

Informative/ Awareness raising and Citizen Engagement

Workshops and Awareness Campaigns: Organisation of dedicated workshops on the design techniques and the implementation of NZEBs to increase awareness.

Participatory budgeting: retrofit in buildings requires a common investment from the residents, participatory budgeting help take decisions among different people that have to prioritize how to invest their money.

Consultations: Understand the concerns, needs and resources of residents in order to better address them to get a positive involvement.

Co-design: Collaboratively design the development and work on the needs and resources of residents.

Drop-in sessions: Use communal spaces for initial contact with residents and raise queries.

Local and permanent technical office: to set a dialogue with the residents, solve doubts and help with technical answers, etc.

Makerspaces to prototype tailored solutions.

Planning

Integrated action plans: Implementation of an integrated action plan to increase the energy conservation and the use of renewable energies in the built environment.

Financial/ Fiscal

Grants/subsidies: Provide reasonable subsidies to investors on zero or positive energy communities. CO2-based taxation of energy carriers for heating. Financial support to supplement general pricing and regulatory policies.

Regulatory

Promote the use of energy conservation and renewable energy systems in buildings.

Define minimum energy performance standards for existing buildings

Lifecycle emissions requirements for construction and renovation projects, products and materials

Efficient pricing and regulatory instruments have to be defined and implemented now to limit the energy costs for society.

Technical

Provision of energy efficient products and services: Set appropriate municipal targets and standards on the implementation of energy conservation and renewable energy systems in local building stock

One-stop shops as a helpful way to combine retrofitting techniques

European Nearly Zero Energy Buildings project: The objectives of the European Zero Energy Project are, (9): i) review and alignment of regulations, policies, incentives and codes, making ZEB mandatory; ii) information and awareness campaigns on the importance of ZEB buildings, involving builders, architects and other building professionals but also schools, local governments and the public in general; iii) training of the industry’s workforce and professionals; iv) the availability of technical tools for designers and builders; v) financing programs, in order to ensure the affordability and viability of ZEBs; vi) Support to modular and technological improvements, supply chain businesses (high performance window manufacturers, for instance) and to smart utility grids.

In parallel, there are many European initiatives on zero energy buildings with a European transnational scope. A list is given below:

Entranze - (Policies to Enforce the Transition to nearly Zero Energy buildings in the EU-27) was a European project aiming to assist policymakers in developing integrated, effective and efficient policy packages achieving a fast and strong penetration of nearly Zero Energy Buildings (NZEB) and renewable heating and cooling technologies (RES H/C) – with a focus on the refurbishment of existing buildings, (10).

MaTrID – Market Transformation Towards Nearly Zero Energy Buildings Through Widespread Use of Integrated Energy Design. A European project aiming to support the implementation of the Directive on the Energy Performance of Buildings and the implementation of Nearly Zero Energy Buildings by 2020 (11). The MaTrID Project Objectives are: i) establishing the general understanding on the advantages and requirements of integrated design (ID) for real estate developers and building owners; ii) improving knowledge on ID; iii) testing the practical implementation of ID on a large scale; iv) developing a common tool-kit for the integrated energy design; v) implementing EU-wide promotion and dissemination activities; and vi) drawing conclusions for a further market adoption of ID in the years after the end of the project.

SouthZEB – The project aims to foster the energy efficiency of the building sector through the adoption of near Zero Energy Buildings (concepts in new or existing buildings). The SouthZEB project develops training modules targeted towards specific professionals (Engineers, Architects, municipality technicians and decision makers) in Southern European countries, (12)

ZEMEDS – The main goal of ZEMedS EU project is to increase the knowledge and know-how on nZEB renovation of schools in Mediterranean climates and give support to several new initiatives on nZEB refurbishment of schools in Mediterranean climate regions, (13).

SustainCO - Sustainable Energy for Rural Communities projects. ‘SustainCo supported the European vision for the energy performance of buildings, that by 2020 all new buildings should be nearly Zero Energy Buildings (nZEB) The SustainCo project aims to raise awareness of, and support development of, low energy building projects, with special emphasis on rural areas. SustainCo aims to increase the visibility of both new-build and renovation, with the aim of capacity and confidence building in the public sector’, (14)

CABEE – CABEE is a transnational EU founded project aiming to create and implement guidelines for definition, procurement, production, assessment and promotion as well as learning about new and refurbished Nearly-Zero-Emission-Buildings (NZEB) and their neighborhoods, (15)

CRAVEzero (Cost Reduction and market Acceleration for Viable nearly zero-Energy buildings): EU Horizon 2020 funded project which focuses on proven and new approaches to reduce the costs of nearly-zero energy buildings at all stages of the life cycle. The primary goal is to identify and eliminate the extra costs for such buildings related to processes, technologies, building operation and to promote innovative business models considering the cost-effectiveness for all stakeholders in the building’s life cycle.

AZEB (Affordable Zero Energy Buildings) - EU Horizon 2020 funded project aimed at achieving significant construction and lifecycle cost reductions of new nearly zero energy buildings through integral process optimization in all project phases.

NERO (Nearly Zero Energy Wooden Buildings in Nordic Countries) – EU Horizon 2020 funded project which develops and demonstrates technical solutions, which significantly reduce the costs of new nearly Zero-Energy Wooden Buildings and districts compared to the current situation.

EPBD-CA (Concerted Action Energy Performance of Buildings) – EU Horizon 2020 funded project reporting on the collective EU-wide overview on the development of EPBD policies across Europe through individual Thematic Reports, including Nearly-Zero Energy Buildings.

In parallel, Build Up is Europe's portal on energy reduction in buildings. It gathers practitioners and professional associations and motivates them to exchange best working practices, knowledge, tools and resources (16).

Some practical suggestions on Best Practices for Affordable Zero Energy Building Design based on existing experience can be found in (23)

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