Author 

Annamaria Belleri (Senior Researcher at Institute for Renewable Energy, Eurac Research).

LinkedIn profile

(Note: opinions in the articles are of the authors only and do not necessarily reflect the opinion of the EU).

Introduction

In order to accelerate the clean energy transition, the European Union set enhanced climate and energy targets, giving a particular emphasis on improving energy performance in the building sector[1]. This regulatory trend has been taken forward in 2020 by the Climate target Plan 2030 [2] and the Renovation Wave strategy [3] which shifted the focus from improving the energy performance during building operation to a complete building stock decarbonisation by 2050 reducing overall GHG emission in the building life cycle.

Considering the number of existing buildings, decarbonising the building stock requires new buildings designed to reach the highest performance to compensate for existing buildings’ emissions. The forthcoming revision of the EPBD is expected to require that ‘all new buildings should be zero-emission buildings, and all existing buildings should be transformed into zero-emission buildings by 2050’. Furthermore, building renovation and new buildings’ construction are considered unique opportunities ‘to improve indoor environmental quality, living conditions of vulnerable households, sufficiency and circularity, increasing climate resilience, improving environmental and health standards resilience against disaster risks and accessibility for persons with disabilities, and enhancing carbon sinks, such as vegetated surfaces”.

In that context, Zero-emission and positive buildings are especially relevant. Zero-emission buildings are buildings with a very high energy performance, which contribute to the optimisation of the energy system through demand-side flexibility, where any very low residual amount of energy still required is fully covered by energy from renewable sources generated on-site or nearby off-site. When the energy balance between renewable energy generated and consumed by the building is positive, it is considered to be a positive energy building since is capable of exporting surplus energy to other buildings or to the network. Accordingly, net-zero and positive energy building initiatives have grown around Europe with the aim of promoting and fostering their implementation.

This article presents the overall framework for the PEB definition, and the latest project results in terms of technology solutions, multiple benefits analysis, and policy recommendations.

Common understanding of Plus Energy Buildings

There is no harmonised definition and calculation method of Plus Energy Building neither in the related literature nor in international standards [4, 5].  

A Plus Energy Building is commonly understood to be a building that generates more energy than it consumes, and feed renewable energy source (RES)-based energy to the grid or other surrounding buildings [6]. In this way, PEBs can support areas with older or listed buildings with architectural constraints, where the transition to zero energy levels would not be cost-efficient or feasible. 

This implies more interaction with the energy grid, which needs to be taken into account in the definition, more than in the case of Net Zero Energy Buildings. In addition, PEBs shall contribute to reducing the energy grid congestion by providing a flexible energy asset that allows buildings and energy communities to act as integrated parts of the energy system and exchange energy (electrical, thermal energy, or other future energy carriers) among them or with the grid. This also enables the accommodation of potential energy demand variations due to alterations of the standard context of users/householders and/or within building communities.

The positive energy balance should be achieved alongside key functional requirements related to occupants’ well-being, users’ expectations and satisfaction, and other material and environmental aspects. Therefore, a user-centred design approach should be adopted for the design of PEBs, i.e., to provide a comfortable and healthy indoor environment for its occupants and raise their awareness on how daily practices impact on the building energy demand and its overall performance. 

Several key aspects of the definition have been discussed among the EU-funded research projects on the topic [6]. These key aspects include: 

• Renewable energy generation sources: on-site RES production must be favoured, off-site could be included if generated near the building (i.e., in the neighbourhood or district) with straight connection to the building’s energy system and under direct control from the PEB. RE supply options should consider the availability of resources, ownership of buildings and other available sites, the performance of the grid in terms of energy mix and transportation, the distance of RE supply from the building, and the availability over the lifetime of the building. 

• In compact or high-rise buildings, the technical and economic viability for deploying RE generation on-site could be limited, jeopardising the positive energy balance. Despite that, considering the user-related energy consumption (i.e., plug loads and electric vehicles charging) can empower end-users and change the designer's mindset towards a more user-centric design. 

• Dynamic matching, smartness, and building flexibility are key assets for an optimal integration with the energy grid, and to leverage plus energy buildings as active part of the energy infrastructure. 

• The energy balance can be calculated over an annual basis in either primary energy or in GHG emissions. However, overall lifecycle impact assessment is recommended to ensure an overall environmental payback, and to raise aware the choices of building materials to be adopted in the construction. 

• User expectations towards indoor environment conditions, and the occupants’ needs, health and socio-cultural practices will be put at the heart of a new user-centric design and operation paradigm. Thus, it is necessary to set key design targets for Indoor Environment Quality and acknowledge the added value of PEBs for the user and society over their lifespan. 

Fostering Residential Plus Energy Buildings: EU-Funded Initiatives

The European Commission has funded several research projects to promote the development of Positive Energy Buildings, in particular in the residential sector, investigating solutions both at the building and neighbourhood levels.

Three projects on new positive energy houses were funded in 2019 under the Horizon 2020 Programme: Cultural-E, EXCESS, and syn.ikia. All the projects aim at demonstrating positive energy buildings over 4 EU climatic regions (mediterranean, oceanic, continental, sub-arctic climates).

H2020 Cultural-E project developed four key technologies for PEBs:

• Cloud-based House Management System

• Active Window System

• Decentralised Packed Heat Pump system

• Smart air movement for thermal comfort 

All of these are tailorable to specific contexts and energy demands while also integrating into modular solution sets [7] which have been evaluated through a comprehensive analysis of building archetypes from an energy, environmental, social, economic, and indoor environment quality perspective. The project is also going beyond the state-of-the-art by mapping cultural and social-related energy habits and comfort expectations [8]. The implementation of the solutions and technologies developed in the project is being demonstrated in 4 case studies: Ostfildern-Ruit (Ostfildern, Germany), Eiksveien 116 (Bærum, Norway), Residenza I Girasoli (Castenaso, Italy) and other demo cases in Leers, France. 

The H2020 Excess project merges technical concepts for Positive Energy Buildings with new opportunities for the generation of renewable energy and self-consumption, as provided by the EU regulation framework and plans. In addition to driving forward the development of building technologies (building energy management system, prefabricated multifunctional façade elements, ground source heat pumps, PVT panels) to enable PEBs in diverse climatic conditions, a key focus of EXCESS lies on facilitating the integration of building technologies. Cost optimal technology packages have been defined and analysed by comparing net primary energy demand and global costs [9].

The implementation of the technology packages developed in the project is being demonstrated in 4 case studies:

• a former industrial complex (Graz, Austria), 

• social housing apartments (Hasselt, Belgium), 

• a residential building in Helsinki, Finland,

• Renaissance palace from the 16th century located in the historical centre of Valladolid, Spain.

The H2020 Syn.ikia project works at the neighbourhood scale and the project concept relies on the interplay between novel technologies at this scale, energy efficiency & flexibility of the buildings, good architectural and spatial qualities, sustainable behaviour and citizen engagement [10]. The buildings in a sustainable Plus Energy Neighbourhood shall be Plus Energy Buildings and are connected through a digital cloud that enables them to share local storage and energy supply units. In a Sustainable Plus Energy Neighbourhood, the geographical boundary is expanded to the entire site of the neighbourhood and includes local storage and energy supply units. Users, buildings, and technical systems are all connected via the neighbourhood digital cloud which is used actively to meet the energy demand shifting and synchronisation on the neighbourhood level, to balance between the supply of sustainable energy and the demand of the buildings and charging of electric vehicles on a district level [11].

Syn.ikia is piloting four real-life Sustainable Plus Energy Neighbourhoods: Fondo (Santa Coloma de Gramenet, Spain), Verksbyen (Fredrikstad, Norway), Loopkanstraat (Uden, Netherlands), Gneis district (Salzburg, Austria). 

In all the three projects, partners explored challenges and opportunities associated with positive energy buildings, the co-benefits and co-impacts related to positive energy buildings and the neighbourhood as well as enabling factors for PEBs market uptake.

More recently, two projects were funded under the programme Horizon Europe (HORIZON-CL5-2022-D4-01-02 - Renewable-intensive, energy positive homes), raising the bar of innovation for positive energy buildings through integrated design and construction concepts that allow maximum flexibility and adaptability to different users' profiles.

REN+HOMES (Renewable ENergy-based Positive Homes) project will develop a methodology for Plus Energy Buildings by creating a new generation of dynamic certificates usable worldwide that will consider design and operation, as well as water and material scarcity.  The technical solutions developed in the project will be targeted to both new construction and renovation and range from prefabricated envelope solutions to IoT applications to geothermal wall systems, BIPV systems and water drainage systems. 

LEGOFIT  will focus on early design actions to accomplish Energy Positive Homes by:

1. developing an innovative holistic design platform targeting both professionals and end-users,

2. integrating active and passive strategies (e.g., envelope, HVAC systems, integrated solutions, including nature-based solutions, etc.) with smart management technologies (BAS, BMS),

3. investigating innovative routes for promoting minimum environmental impacts by the smart use of solid and liquid residues generated during building life cycle stages and

4. fostering a sustainable stock of buildings by guaranteeing not only the fulfilment of sustainable criteria (economic, social, environmental) but also to the enhancement of smart readiness of buildings. 

Conclusions

The considerable potential of the European residential building sector in attaining positive energy goals through energy-efficient technologies and renewable energy production has gained recognition among policy makers. Facilitating the integration of building technologies through a centralized control system that synergically operates them holds the key to significantly lowering the lifetime costs of PEBs, thereby rendering them more affordable to a broader segment of the population.

In the European journey towards a complete building stock decarbonisation and a carbon neutral society, the current challenge regards the sustainability of these solutions and hinges on their multifaceted impacts, encompassing environmental, social, and economic aspects. PEBs design and construction concepts should involve considerations like reducing embodied carbon emissions from materials and ensuring the reutilisation and recycling of elements, components, and materials at the conclusion of their lifecycle.