Acknowledging the significance of energy efficiency in the building sector, and more in particular of the need for energy retrofitting of the existing building stock, the scientific community and the construction industry have turned to the development of innovative materials and systems that can be applied to existing buildings to drastically reduce their energy consumption. The European Commission finances various activities to support further research, as well as to boost the introduction of such innovative technologies in the market. This Overview Article presents the state of the art regarding innovative technologies and relevant EU-funded projects.
The building sector’s key role in enabling the EU to deliver on its Paris Agreement commitments and becoming more stable, competitive and sustainable, has been repeatedly highlighted. So is the fact that, for the EU to decarbonise its building stock, the vast majority of the buildings currently standing would need to be renovated. For these reasons, the Commission's proposed revisions to the Energy Performance of Buildings Directive (EPBD) and the Energy Efficiency Directive (EED), published as part of the Clean Energy for all Europeans legislative proposals, specifically address building renovation and, in parallel, encourage the development of innovative technologies that support the efficient operation of buildings.
The European Commission has thus recognised the need for the development of new materials and systems which have shown promising results in reducing energy consumption, compared to more conventional technologies. Various research projects are financed by the Commission, e.g. as part of the Horizon 2020 research and innovation programme and its precursor FP7, in order to make innovative systems technologically mature, technically feasible and commercially exploitable in the near future. Some of these technologies and examples of relevant EU-funded projects are described below.
The vacuum tube is intended to reduce heat losses through glazed surfaces. This technology includes several glass tubes with vacuums inside, sandwiched between two glass surfaces, with non-vacuum parts of the structure filled with a low thermal conductivity gas, i.e. argon. Different variations of the technology are being tested in order to define the geometry with the best thermal properties. Vacuum glazing technologies are evaluated within the scope of various retrofitting projects, e.g. the Holistic energy-efficient retrofitting of residential buildings project - HERB.
There are two variations of self-cleaning coatings: hydrophobic and hydrophilic. Both types clean themselves with water, using different mechanisms. However, hydrophilic coatings have the additional property of being able to chemically break down adsorbed dirt in sunlight. The technology of self-cleaning coatings has developed rapidly in recent years, however the field is far from mature. The development of new materials that can be easily applied to facades, with both self-cleaning and de-polluting properties, would be a significant step towards improvements in urban quality of cities. The EU funded BRESAER project aims to develop and demonstrate an innovative envelope system that uses cost-effective, adaptable solutions for building refurbishment, including thermo-reflective, self-cleaning coating plus PV film.
Phase Change Materials
Phase Change Materials (PCMs) can be described as mixtures of chemicals that have freezing and melting points above or below the water freezing temperature of 0°C (32°F). PCM materials are ideal products for thermal management solutions as they store and release thermal energy during the process of melting and freezing (changing from one phase to another).When such a material freezes, it releases large amounts of energy in the form of latent heat of fusion, or energy of crystallisation. Conversely, when the material is melted, an equal amount of energy is absorbed from the immediate environment as it changes from solid to liquid.
Various EU funded projects examine the use of PCMs in building retrofit, among which the 'New advanced insulation phase-change materials - NANOPCM FP7 EU-funded project which focused on the development of nanotechnology-based thermal energy storage materials compatible with conventional building materials, and the FP7 HESTOR project that aimed to develop a novel HPCM-based thermal storage unit system for enabling optimised performance and enhanced energy cost savings in HVAC systems.
Aerogel and Vacuum Insulated Panels
Aerogel and Vacuum Insulated Panels (VIPs) are the two types of commercially available insulation materials referred to as super insulation materials.
Aerogel materials exhibit the lowest thermal conductivity of any of the solid or porous materials. Aerogel also has extremely high hygroscopic properties that make it a very strong desiccant. However, it is considered a hindrance in building applications, as it is difficult for installers to work with the blanket form it is supplied in.
Vacuum Insulated Panels are an innovative technology in which a rigid fumed silica core material is wrapped in a sealed air tight material (such as aluminium) from which the air has been evacuated. With the air removed from the material, its insulation properties are five to ten times greater than conventional insulation. The coating film is composed of plastic polymers, alternated with metal layers that prevent gaseous penetration of the core. VIPs have the lowest values of thermal conductivity between the insulating materials currently available on the market, as the thermal conductivity at the centre of the panel can be as low as 0.004Wm-1K-1. Thus, the thickness of the material can be very low and still achieve the required U-value. The application of Aerogel and Vacuum Insulated Panels in energy retrofit is investigated by various projects.
Among those, the main objective of the FP7 RESSEEPE project was to technically advance, adapt, demonstrate and assess a number of innovative retrofit technologies, including envelope retrofitting (ventilated facades, aerogel-based superinsulating mortar, wooden insulating wall panel and VIP panel), but also integration of RES (PV, thermal collectors), energy storage systems (thermal storage and PCMs), nanotechnologies and smart materials (EC/PV Windows) and others.
The FP7 NanoInsulate project developed durable, robust, cost-effective opaque and transparent vacuum insulation panels (VIPs) incorporating new nanotechnology-based core materials (such as nanofoams, aerogels and aerogel composites) and high-barrier films, that are up to six times more energy efficient than current solutions.
Currently, the H2020 AMANAC project aims to create a collaboration and coordination platform within the Energy-efficient Buildings Public Private Partnership (EeB PPP) Advanced Materials and Nanotechnology projects, whose activities address development of (nano)materials, components and systems for the improvement of energy efficiency in buildings, for specific thematic areas, among which superinsulating materials (Aerogels & Vacuum Insulation Panels) and their application in the development of construction components, but also on embodied energy, smart windows and lightweight components.
Passive zenithal light guides
Passive zenithal light guides are a type of Tubular Daylight Guidance Systems, which are systems that can channel daylight to the core of buildings. Light pipes can be horizontal or vertical and they can even have bends, in order to suit any application. During the last few years, light pipe manufacturers have tried to incorporate artificial lighting into traditional light pipes, so that the system can produce the desired interior illuminance levels under any sky conditions. The more sophisticated versions incorporate Light-Emitting Diode (LED) lamps, with specially designed optical systems to maximise system performance, combined with daylight-linked controls, in order to achieve greater energy savings.
Passive zenithal light guides are considered within the framework of the HERB project mentioned above.
PV Systems and Façade Integrated PV Systems
Innovative PV systems integrated into the building façade and/or roof comprise of high performance thin-film PVs. The benefit of PV thin-film is that it reacts better to low or indirect sun light and can operate on cloudy days. A study by KIC InnoEnergy concludes that Levelised Cost of Energy savings of at least 44% are anticipated for thin film PVs.
The FP7 DIELECTRIC PV project developed a novel light-trapping approach for improving the absorption of thin-film silicon (Si) solar cells that lead to higher-efficient thin-film, flexible solar cells.
Figure 1: Illustrative graphical abstract image of the article: Design of optimised wave-optical spheroidal nanostructures for photonic-enhanced solar cells. Manuel J.Mendes, Andreia Araújo, António Vicente Hugo Águas Isabel Ferreira, Elvira Fortunato, Rodrigo Martins, Nano Energy, Vol.26, 2016 [Source: Nano Energy Journal, Elsevier Ltd.]
The recently launched H2020 Uniting PV project examines the application of silicon solar cell technology to revolutionise the design of thin-film solar cells and enhance their efficiency, cost and stability.
Solar Thermal Heating Systems
Advanced evacuated tube solar collectors, where the absorber is treated with a selective Tinox coating to maximise the solar energy absorbed and minimise heat loss through radiation, are used in novel applications. These solar collectors could form a component of roofing and facade structure but can also be developed for heating hot water and as a heat source for heat recovery or solar powered ejector cooling.
The European Commission publication “Overview of support activities and projects of the European Union on energy efficiency and renewable energy in the heating & cooling sector” provides an overview of the EU-funded projects in the area of heating and cooling, including projects that have supported the market uptake of sustainable heating and cooling technologies including solar thermal, bio-energy, shallow and deep geothermal as well as combined heat and power and district energy systems.
Gas absorption Heat Pumps
This type of system takes advantage of freely available energy from the air or ground and brings it to a higher or lower temperature for building heating or cooling. Gas absorption heat pumps combine condensing boiler technology with a zeolite/water-based thermal heat pump module.
The HEAT4U FP7 funded project designed residential absorption heat pumps driven by natural gas to produce heat and domestic hot water cost-effectively.
Figure 2: Implementation of Gas Absorption Heat Pump (GAHP) [Source: Gas Absorption Heat Pump solution for existing residential buildings (HEAT4U) project - Description of the Project, 2011]
Viable deep energy renovation projects in buildings require, among others, the removal of regulatory, social and economic barriers, and easy access to technological innovations and skilled professionals. With the proposed amendments of the two relevant EU directives, the European Commission is tackling regulatory, social and economic barriers by addressing energy poverty and the mobilisation of smart financing for building renovation and, in particular, for strengthening the links between public funding for building renovation and energy performance certificates. The expansion of funding available to invest in research and development of innovative energy efficient materials and systems through the Horizon 2020 Work Programme 2018-2020 will ensure that these are fully exploited, to make their application in energy retrofit plausible and cost-effective. In parallel, with the European BUILD UP Skills initiative, training of professionals in the proper application of innovative technologies during renovations is established at European level.