Advantages in a vacuum

In the world of insulation technology, vacuum insulation panels (VIPs) are the top of the line – especially when filled with HDK^® pyrogenic silica from WACKER. The Vitec company, based in Ilsenburg, Germany, manufactures custom VIPs upon request for use in fire doors, cold-storage rooms or in construction.

Vacuum is what physicists call the absence of material in a given space. As a general rule of thumb, evacuating the residual air within an insulation panel increases its insulating effect by a factor of six or seven.

The underlying principle is quite simple: by preventing the gas molecules of the air from transferring heat, a vacuum can produce extremely low thermal conductivity values of less than 0.004 W·m−1·K−1. This allows manufacturers to create insulation panels that, while just two centimeters thick, have the insulating capacity of standard panels 12 to 14 centimeters thick. Applications cover a wide range: VIPs do an equally good job of protecting thermally insulated packaging, refrigeration units, cold-storage rooms, hot-water tanks, fire doors, building exteriors, floors and flat roofs from heat and cold.

The use of vacuum insulation panels has allowed Torlit to reduce the thickness of their door insulation from 110 millimeters to 20. Joachim Luther, the managing director of both Torlit and its offshoot Vitec GmbH, put forward another key argument for using HDK^® as the core material for VIPs: “The rule of thumb is that if something insulates well, it burns well too.” But, he explained, silicas are non-flammable, which makes them ideal for fire doors. “Thanks to silica, we’ve been able to make our doors thinner – and lighter too – while at the same time making them better insulators and improving fire safety,” says Luther, summarizing the advantages.

As specialists for fire doors and doors for cold-storage rooms, Torlit engineers are very familiar with the advantages and disadvantages of many insulating materials. The use of mineral wool, for instance, is discouraged in cold-storage areas, because it draws moisture and then loses its insulating properties. Polystyrene, the insulating material used most often in construction applications, needs to be very thick. And the first generation of Torlit fire doors used inorganic foams based on ceramic particles that had been formulated with phenolic resins, even though these were found to be quite brittle. After a brief experimental phase, the Torlit engineers ultimately decided about ten years ago to make their doors almost exclusively with vacuum insulation panels filled with HDK^® from WACKER.

Fire doors and doors for cold-storage rooms are generally customized and produced on demand. The built-in vacuum insulation panels are made individually as well so that they fit flush in the doors. That means that Torlit relies on a very fast, flexible supply of VIPs.

“We deliver fire doors of all sizes within two to three weeks, which wasn’t convenient as regards the time it takes VIP manufacturers to deliver – they often need six to eight weeks,” says Luther. “To produce and deliver our doors faster, we absolutely had to make the VIPs ourselves.”

Once compacted, the molded panel made from the HDK^® blend is placed in a specially designed foil bag. The foil consists of multiple thin layers of polymer and metal, both to ensure the most effective possible barrier to gas and moisture penetration and to maintain the insulating properties of the VIP for as long as possible. The engineers at Vitec anticipate that their vacuum insulation panels will be able to serve their purpose for decades. And this is another reason why HDK^® is superior to alternative fillers: glass-fiber cores and polymer foams, for example, age faster than pyrogenic silica, because pressure rises more quickly within these cores, and the insulating properties then deteriorate accordingly.

Certain specialty applications – such as insulation for flat roofs and roof-top patios – require particularly robust panels, and for these the Vitec product line includes VIPs that are encapsulated with an extremely hard, glass-fiber-reinforced plastic. “You can even walk on it at the construction site and nothing will happen,” says Ralf-Geoffrey Frohnwieser, a member of the Vitec sales team.

For building insulation, the company also offers VIPs with an edging roughly ten millimeters thick and made of traditional insulating material (extruded polystyrene; XPS) so that the panels can still be worked with. “That allows you to compensate for typical construction tolerances,” Frohnwieser explains. It also suppresses heat transfer in the joints between individual VIPs. VIPs for roof and exterior insulation are custom-made and delivered to the builders along with installation plans.