© GLASSX, Gaston Wicky

Germany is already the world champion in energy efficiency. According to a study by the American Council for an Energy-Efficient Economy (ACEEE), no other country uses energy so thoughtfully and sparingly. Nevertheless, energy consumption specifically in the building sector is still too high for the country to meet its self-imposed climate targets and to make the Energy Transition a success. The current building rehabilitation programmes are making a significant contribution: over 3.8 million homes have been built or refurbished to date under the Federal Government's CO2 Building Renovation Programme alone. But that on its own is not enough.

For that reason, scientists are working on an even more energy-efficient "House of the Future." To this end they are developing new ideas and approaches as well as innovative technologies and materials. "Precisely in the building sector, energy-efficient technologies can make an important contribution world-wide to reducing energy consumption and thus CO2 emissions and the cost of energy to consumers, society and the public sector," says State Secretary Rainer Baake, stressing the importance of the research effort.

Room climate control with a difference: walls and ceilings regulate the temperature

One area of research by EnOB is construction materials that can control the temperature in indoor areas just like an air conditioning system – but without any technology at all. To make this work, phase-change materials, or PCM for short, are built into walls and ceilings. Typical examples of PCM are salt hydrates – salts that contain water. When heated, salt hydrate changes its physical state from solid to liquid, storing the heat absorbed. Built into walls or ceilings, it takes up excess room heat, so that the temperature does not get too high during the day. When the room is ventilated at night, the PCM releases the heat again and instead serves as a cold reservoir which is tapped next day to keep the room comfortably cool. This either dispenses with the need for an air conditioning system entirely, or it can be run with vastly reduced energy consumption. Besides in walls and ceilings, PCM can also be incorporated into plaster, facing tiles and panels, or into façade elements.

Double benefit: the roof that insulates and generates energy at the same time

In future, a building's roof will also perform multiple tasks. Up to now, rooftop solar panels have been used to generate electricity or heat. However, these panels have been mounted on top of the roof itself. In the context of EnOB, researchers from the technical university in Aachen have joined together with partners from industry to develop a roof that itself generates energy and at the same time also provides good insulation. It consists of rectangular elements made of fibre-reinforced concrete. This is concrete that is reinforced with a mesh of textile fibres.

The top layer of the concrete elements incorporates mats containing thin channels. Water running through these channels is heated when the sun shines. This heat can be used, for example, for heating rooms or for hot water.

Since the concrete parts are lightweight modules, they can be transported to the construction site without major effort and installed both in new and renovated buildings. And as if that were not enough: the researchers are already working on applying the idea to the entire façade.

Plug & play: renovating with ready-made façade elements

In the context of façades the researchers are looking for even cheaper and simpler rehabilitation approaches. One promising EnOB project is concerned with façade elements that are fully prefabricated in the factory. Each element consists of a window with frame, a terminal box for power or internet cables, and an insulant rim. The element is simply pushed from the outside into the gap where the old window used to be and fully insulates the existing façade at this point. The remaining façade area between the installed windows can then be insulated using the usual methods. This makes renovating multi-storey houses much easier and cheaper overall.

Clear as daylight: checking windows made easy

For house-owners who do not want to wait for the prefabricated façade elements but are already thinking about replacing their windows the EnOB researchers have developed a special instrument. It is called Uglass, is compact, portable, and makes it possible to check the thermal insulation properties of the windows currently installed. Because some windows don't deliver what the manufacturers promise.

Using Uglass and the associated software is so easy that it does not take any specialist knowledge: domestic technical designers, assessors and consultants from the window, façade and glass sectors can now appraise the quality of the windows in legacy buildings easily and quickly.

Research on the device has led to a further innovation: a sensor for assuring quality in the manufacture of insulating glass. This sensor makes it possible to measure very precisely how much inert gas there is in the gap between the panes. The system works "on-line," that is to say during the production process, and takes just a few seconds. It enables the manufacturer to make reliable claims regarding the insulating properties of their products. That enhances the quality of the windows used in new buildings and rehabilitation projects – and thus also benefits consumers.

Pretty intelligent: networked buildings think along

A completely different approach to reducing the energy demand of buildings involves promoting the efficient and intelligent use of energy – here the buzzword is "grid-interactivity of buildings." That means: a house will in future not only consume energy but also interact with local electricity and heat networks as a generating plant and energy storage unit. For example a grid-interactive building could re-schedule its power requirements: when there is too much solar and wind power being fed into the electricity grid, the building takes advantage of this surplus to cover its current needs and replenish its storage reservoir. For storage the electricity is converted into heat or cold and immobilised in special walls and ceilings in the building (cf. PCM, above). If the building later needs a lot of energy but there is little solar and wind power coming into the grid, it can tap this stored reserve. "There is much to indicate that, in addition to energy efficiency, grid-interactivity is going to be a further essential design consideration to be taken into account in future building planning," explains Karsten Voss, Professor of Building Physics and Technical Services at Bergische Universität Wuppertal, EnOB's current research hub.

Neatly bundled: a new network for research initiatives

Besides the EnOB, the BMWi is also providing support for further campaigns in the field of energy research: EnEff:Stadt and EnEff:Wärme are dedicated, respectively, to reducing the energy consumption of neighbourhoods or even whole cities and to modernising and expanding other local and district heating systems. A third campaign, "Low-temperature solar-thermal conversion," is aimed at using more solar energy for heating buildings.

The BMWi has bundled all four initiatives in the recently founded "Research network on energy in buildings and neighbourhoods." The aim of the network is to optimise research still further and to ensure that the findings can be applied in practice more quickly. The two-day kick-off event held in Berlin at the end of March brought together more than 200 participants from research, business, professional associations and politics for an informal exchange of ideas. The many and diverse stimulating suggestions raised at the meeting provide inspiration for future funded assistance-strategies.