When it comes to unused potential for saving energy, buildings can’t be beat: They are responsible for 28% of the world’s energy consumption, a figure that rises to 45%, when only Western countries are taken into consideration. According to the German Environmental Agency (UBA), an energy-retrofit programme can reduce a building’s primary energy demand by up to 90%. The European Union (EU) has responded by strengthening its directives for the overall energy efficiency of buildings: Starting from 2021, for instance, all new buildings in the EU are to be constructed to meet virtually the same standards as zero- energy buildings. These buildings should produce electricity in an amount corresponding to their energy consumption.

Given the established fact that good thermal insulation is a key factor in making buildings more efficient, growing demand for building efficiency is resulting in thicker and thicker insulating materials. However, space is particularly limited and expensive in city centres, and fire-safety standards are high. For this reason, architects are on the lookout for lean solutions that can meet the twin demands, while leaving as much room as possible for creative design.

The recognition of the trend has given rise to a silicon-based heat insulation panel, made of synthetic, amorphous silica. Its thermal conductivity (λ) of just 0.019 W/mK makes it by definition a super-insulator, performing even better than air at rest, which has a λ value of roughly 0.025 W/mK. This means that the insulation panel can be up to 50% thinner than conventional mineral insulating materials and yet achieve the same effect.

In addition to having super-insulating properties, the panel is categorised as a Class A building material (non-flammable), which presents quite an unbeatable combination. What makes this possible are the mineral nature and the fine porous structure of silica. We have long known that a form of synthetic, amorphous silica is an established first-class insulating material for radiant heaters, where the temperature of the heating coils can reach several hundred degrees Celsius. A layer of the silica, up to a maximum of only about two centimetres in thickness below the stovetop, absorbs the heat to the point where electric cables can be placed, nearby.

The high-tech insulating material is hydrophilic, however. If it comes into contact with water its inner adhesive forces become so powerful that they can destroy the fine porous structure. When this happens, the material not only changes its macroscopic form – it also loses its excellent insulating properties, which is why the construction industry has long resisted its use as an insulating material.

The breakthrough to solve the challenge posed by water came in the form of a new technology called ‘core hydrophobisation’, which makes the entire pore structure – and not just the surface – water repellant. As a result, water vapour can diffuse through the material without destroying the structure or condensing inside it. And that paved the way for its use in the construction industry.

Plus, thanks to core hydrophobisation, the new insulating material is not susceptible to mould, which eliminates the need for fungicides and biocides. The fact that it is based on mineral raw materials not only explains its strong fire-retardant properties but also emphasises the fact that unlike other types of insulation, it is recyclable. If preferred, it can also be easily disposed of as part of normal construction waste – a cost benefit in the construction industry, which always has its eye on the bottom line.

EFFECTIVELY SUPPRESSES HEAT TRANSFER
There are three ways that undesirable heat conductivity can arise in insulation: Solid-state thermal conductivity, heat transfer via gases (which is inhibited, for instance, by the vacuum in multi-glazed windows), and heat transfer via infrared radiation.

The insulation material effectively limits thermal conductivity and heat transfer. The solid-state matrix of the silica used is specially treated in such a way that the contact surface – and, thus, the transfer paths between individual solid particles – is kept as small as possible, minimising thermal conductivity. In addition, the very tiny pore spaces limit the energy transferred by gaseous conduction. Thermal radiation doesn’t stand a chance with the insulation panel, either.

The material and its fine pore structure confer a second advantage: Its thermal conductivity, unlike that of traditional insulating materials, is almost not temperature-dependent. As a result, the new insulation panel not only prevents the interior from cooling during the winter, but it also keeps it from heating up in the summer, when building exteriors can easily reach temperatures of up to 80 degrees C. This pays off especially in buildings made of lightweight panels. Here, rooms easily become overheated, because the shade from blinds alone is not enough.

STRENGTH IN INDOOR ENVIRONMENT AND FIRE PROTECTION
The reason why the thermal conductivity of the new insulation panel is almost not temperature-dependent is its favourable temperature-amplitude ratio – a complex interplay of specific storage capacity, density and thermal conductivity. The ratio describes the phase shift in the temperature maxima, observed when heat is transferred through an external wall. Studies conducted by the Bavarian Center for Applied Energy Research (ZAE), in Würzburg, Germany, have shown that in walls insulated with the insulation panel, heat takes eight to 12 hours to reach the interior wall – in other words, not until nighttime, at which point the air outside has cooled, and ventilation from windows provides a pleasant ambient temperature.

Since the time of emergence of the new panel, the team of developers of the panel has taken an intense look at the needs of customers and end consumers. Using numerous reference objects, the team members have been able to demonstrate its performance.

The most recent example can be found in the historic centre of Düsseldorf, where the team insulated the ceilings of the basement and the underground parking garage of a historical landmark building, to which a modern extension had been added. The structure of the underground garage and the sprinkler system of the building were to be preserved to keep costs down, even though they left little space for thermal insulation or fire- protection. The structure of the modern annex needed to be updated, accordingly.

The project played to the strengths of the new insulation panel, which offers strong fire-retardant and thermal insulation properties for the basement ceiling while protecting the sprinkler system from freezing temperatures – all in a very little space. The insulating layer is only 40 mm thick, whereas traditional insulation would have required a much thicker layer.

SUITABLE FOR INSIDE AND OUTSIDE THE BUILDING ENVELOPE

The new insulation panel is suitable for cavity insulation for load-bearing, external walls, for interior insulation, for insulating rain-screen cladding and for concrete sandwich elements. Within the facade itself, the insulation can be combined with ceramic tiles and with elements made of glass, metal or concrete – even with PLEXIGLAS. In quite a path-breaking move, the combination of the insulation panel and PLEXIGLAS has been used for building exteriors. Thanks to its heat transfer coefficient of 0.15 W/m2·K, the panel only has to be 12 cm thick to achieve passive building standards, using 90% less heating energy than a traditional building.

MORE FREEDOM FOR COMPONENT GEOMETRY

Research work on the new insulation panel hasn’t stopped there. In order to free up more options for component geometry, there are plans to offer the material in granulate form. Their ability to fill cavities means that granulates can be used for insulating reactors or boilers, for example.

For this to work, the granulate must be mechanically stable, and it must be possible to control its pore structure, as this has a critical impact on its thermal insulation properties – if the structure is destroyed by stirring or shaking, the insulating properties will be lost. The team of developers is currently working on adjusting the granulation process for silica in order to optimise density, pore size and mechanical stability, while maximising cost effectiveness.

Overcoming the hurdle would also clear the way for its use as insulating filler for mineral-based construction products and coatings. This, in turn, would open up the possibility of manufacturing safe-touch and thermal insulation coatings, which differ in terms of thickness. For safe-touch coatings, just a few millimetres are all it takes to prevent a hot surface from damaging skin on contact. Industrial occupational safety would be one potential application.

Thermal insulation coatings take this a step further. Unlike safe-touch coatings, they prevent energy from being lost in the form of heat transferred to the surrounding air. This, however, requires thicker coatings of several centimetres.

While these developments are far from being ready for the market, the team behind the development of the panel has already sent granulate samples to an initial group of customers. The move marks a return to familiar work habits – looking to the needs of the market, even at an early stage in the process, and incorporating customer feedback into the ongoing development process.