A zero-energy building is a building with zero net energy consumption, meaning that the total amount of energy that it consumes throughout the year is supplied from onsite renewable sources. Achieving zero-energy status requires a two-pronged approach, where the latest construction techniques are combined with renewable energy technologies in a holistic approach that simultaneously reduces the buildings’ energy demand while increasing its onsite energy production capacity.
Buildings are responsible for 40% of energy consumption and 36% of CO2 emissions in the EU and heating consumption in the residential sector in the EU has been calculated at 1702 TWh/y1. Cooling, while currently accounting for a significantly smaller share, is expected to see a major increase in demand in the mid to long-term. Consequently, technologies that contribute to reducing the heating and cooling requirements of a building, and that efficiently supply its heating and cooling needs from renewable sources, will be critical in achieving a building’s zero-energy status, and go a long way towards decarbonising the residential sector in Europe.
For new build, significant decarbonisation can be achieved relatively easily, by state-of-the art intelligent building design combining the latest insulation materials with renewable energy systems and other techniques in a holistic approach2, subject only to cost constraints. Indeed, the European Parliament’s Energy Performance of Buildings Directive requires all new buildings to be nearly zero energy by 31 December 2020. All new public buildings should achieve this target by 31 December 2018. However, the challenge is more daunting when it comes to the existing building stock. The replacement rate of the existing housing stock is very low (1-1.5 % per year), and reorganisation of the sector is a very complex task due to its extreme fragmentation: more than 50% of residential buildings are privately owned by individual private owners. Energy renovations in existing buildings have to cope with the structure and configuration of the building, which often limit efficiency or applicability of the technical options available.
The Horizon 2020-funded BuildHeat project aims to address the challenges posed by the existing residential building stock, by elaborating systemic packages for the deep rehabilitation of residential buildings and developing innovative technologies to facilitate their renovation. To ensure the large-scale entry to market of the new technologies, the project will also devise inventive financial instruments to enable large public and private investments. Finally, to increase awareness and stakeholder involvement, the project will engage with stakeholders all along the construction chain – from owners, to professionals, to investors - from the very beginning and throughout the building life cycle.
In order to increase the market penetration of its residential deep energy rehabilitation solutions, BuildHeat will ensure that these solutions offer high energy performance, comfort and a healthy home environment. The solutions will also be unobtrusive and easy to install and be scalable (from dwelling to district level) in terms of energy management and financing. The systemic renovation packages proposed by the project will exploit opportunities offered in terms of RES availability at building level (i.e. aero-thermal and solar energy). In designing the systems, attention will also be paid to the final energy consumption, which is related to the users’ annually incurred cost; to the primary energy, which is related to the overall environmental impact; and to the capital cost.
With respect to the technologies used, the project will investigate photovoltaic-driven air-to-air heat pumps, with integrated domestic hot water production and power storage capability. This innovative heat pump system will combine renewables at building level with ambient heat recovery to supply the buildings’ heating and hot water needs. The project will also work with centralised heating systems, incorporating warm water storage tanks and local solar thermal collectors in a systemic approach to space heating and domestic hot water supply. Both of these technological approaches will integrate compact thermal energy storage, facilitating the shift of demand from peak to off-peak periods and making it possible to reap the maximum benefits from the renewable energy source.
The project will also develop a façade system that allows easy setup of passive components, such as insulation, windows and shading systems, with active elements such as PV panels and solar thermal collectors. Efforts will also be undertaken to address envelope improvements, with a view to significantly reducing the buildings’ heat needs, while at the same time controlling the risk of overheating. The approaches used in the systemic upgrade packages will be standardised, facilitating the easy integration of both the passive and active components.
Another project taking a systemic approach to the retrofit of the existing building stock is the Horizon 2020-funded E2VENT project. Like BuildHeat, E2VENT aims to develop, demonstrate and validate a cost-effective, highly energy-efficient, low-carbon system for retrofitting residential and commercial buildings. The project will achieve nearly zero energy building retrofit standards using smart modular heat recovery units (including thermal storage) along with high efficiency photovoltaic units, HVAC systems and high performance adapted products for external thermal insulation.
The technologies developed will be integrated into a ventilated façade, operation of which will be controlled by a real-time intelligent façade management system. This system will use weather forecasts to predict the level of decentralised electricity production, which will be correlated with the building’s energy (electrical and thermal) demand, enabling the most efficient use of energy from renewable sources. The use of heat recovery units and other variables, such as the number of photovoltaic cells, natural lighting strategies, and the thickness of the insulation can all be adjusted depending on the characteristics of the building. This makes the E2VENT system versatile and adaptable to different building types and climates. The project’s holistic approach, incorporating active and passive elements, will result in energy savings of more than 40% and a reduction of at least 40% of CO2 emissions, thanks to the primary energy savings.
If the retrofit solutions developed by BuildHeat, E2VENT and other EU-funded projects are to have the desired impact on energy efficiency in the residential sector and achieve their full potential in contributing to the targets set in the Energy Performance of Buildings Directive, it will be necessary to target the wider community of building professionals and owners in order to raise awareness and increase the market uptake of these systems. To this end, both projects include stakeholder engagement components. As regards new build, the outreach efforts are supported by the Promotion of European Passive Houses (PEP) project. Funded by Intelligent Energy Europe, this project aims to promote the potential of the passive house concept in Europe by developing information packages and design tools for passive houses, organising workshops, symposia and conferences, and through an international passive house website.
2Such techniques may include thermal storage, intelligent building controls, shadings and passive cooling, efficient heat exchangers for ventilation, connection to a low carbon heating and cooling grid, etc.