.

Fig. 12: Building elements with vacuum insulation – selection from a manufacturer’s product range.
© Variotec

Fig. 13: The lamination of VIP elements is beneficial for construction site operations.
© IGEL, Wismar

Fig. 14: VIPs laminated with rubber granulates can be walked on without causing damage.
© Porextherm
6 / 17

VIPs for the market

In order to launch new construction materials on the market, not only must their functional efficiency and practicality be proved but various other parameters must be clarified as well. A substantial aspect is, for example, fire protection. Particularly with vulnerable vacuum insulation, durability and quality assurance also play an important role for its long-term success.

There are currently no generally approved technical standards for vacuum insulation panels (e.g. DIN standards). Therefore in order to use them in accordance with the respective building regulations of the various German federal states, they have to have a “allgemeine bauaufsichtliche Zulassung” (national technical approval– abZ). If no abZ is available for the product, it is necessary to obtain approval in individual cases in accordance with the respective federal state building regulations, which is a costly and timeconsuming process. However, four manufacturers now offer VIP products with an abZ – and the trend is increasing:

  • va-Q-tec AG, Würzburg;
  • Porextherm Dämmstoffe GmbH, Kempten;
  • Variotec Sandwichelemente GmbH & Co. KG, Neumarkt/Oberpfalz;
  • Vaku-Isotherm GmbH, Rossau.

The VIP products that have an abZ are listed in the “Verzeichnis der allgemeinen bauaufsichtlichen Zulassungen, Zulassungsbereich Baustoffe und Bauarten fürden Wärmeschutz” (Directory of national technical approvals for construction products and types of construction for thermal insulation) published by the Deutsche Institut für Bautechnik (DIBt). Each national technical approval specifies the object being approved, its area of application, its properties and the composition of the construction product. It also stipulates the manufacture, packaging, transport, storage and labelling as well as the necessary quality assurance measures. For designers, decisive are the design and measurement stipulations, in particular the design value for the thermal conductivity to be used, the minimum thermal insulation and the respective fire protection classification. An abZ is generally issued for five years and can be revoked.

Fire protection

All VIPs with a national technical approval are classified as normally inflammable (Construction Material Class B2 to DIN 4102). In accordance with fire protection requirements, unprotected VIPs can only be installed in the external walls of the building envelope up to a height of seven metres. Laminating the elements with corresponding protection layers enables them to be used up to highrise limit (Construction Material Class B1).

Recycling and ecological balance

With VIPs that have already been rejected in the factory or on the building site because they are damaged, the core material can be directly used again by grinding and repressing it. The envelope films made of metallised polymer composites can only be thermally recycled. With polymer-aluminium composite films with aluminium layer thickness from 6 μm, it is possibly worthwhile recycling the aluminium.

Once VIPs reach the end of their service life as a result of “losing the vacuum”, they could in principle be sorted and recycled. It is assumed that silica used over a longer period of time in the VIP core can still be reused as part of cores once it has been separated from the fibrous materials and opacifiers and has undergone a drying process. Much more complicated is the recycling of bonded elements, such as those laminated with other materials or composite structures.

For VIPswith coresmade of silica and silicon carbide, comparative ecological assessments conducted in Switzerland on glass wool, expanded polystyrene and VIP insulation materials showed that the environmental impact of VIPs is comparable to expanded polystyrene. Although the high proportion of electrical process energy used for manufacturing fumed silica has a negative effect on the ecological balance, this is compensated for by the considerably improved thermal insulation during its application.

Service life

VIP elements age: permeating gases gradually but continually increase the thermal conductivity. Since the ability of the film and seams to act as a barrier againstwater vapour and gases depends on the humidity and temperature, the respective environmental conditions have an impact on the lifespan. Particularly higher temperatures facilitate the influx of gases. Tests conducted over several years in laboratories and in practical applications along with simulations and rapid test procedures indicate, however, that the thermal conductivity of VIPs used in the construction sector only increases marginally across several decades. The thermal conductivity design values specified in the national technical approvals particularly take into account, among other things, the expected ageing for the first 25 years. Depending on the product, these should lie between 0.007 and 0.010 W/(m K), which means that a lower heat transfer is to be expected during the first 25 years of use. This may only increase above the design value after this period of time.

Quality assurance and testing procedures

Because VIPs only provide optimum thermal insulation if the vacuum is intact, this technology requires – and to a much greater extent than with conventional thermal insulation materials – a quality assurance and monitoring system for the entire manufacturing and processing stages.

The national technical approvals from the DIBt in themselves prescribe strict, factory-based production inspections and regular monitoring from external parties, whereby in some cases it has to be checked daily whether the raw materials, properties, dimensions, thermal conductivity, compressive strength and internal pressure comply with the specifications stipulated in the respective approval.

Manufacturers who are members of the ‘Vacuum Insulation Panel Product Group’ within the Güteschutzgemeinschaft Hartschaum e.V., an European quality assurance association for thermal insulation products, even subject their products to additional controls that go beyond those required by the national technical approvals. Products that pass the testing procedure can be furnished with the quality mark according to RAL-GZ 960.

One manufacturer, however, is taking a different approach. A special, patented sensor enables him to carry out relatively precise controls of each individual panel with relatively little effort.

Although the production takes place under controlled conditions, with trained personnel, and ensures a high product quality, the transport, storage on the construction site and, in particular, the handling on site present a particular risk for VIPs. The DIBt has therefore stipulated in its national technical approvals for VIP products that the installation of VIP elements may only be carried out by trained personnel, i.e. personnel who are sufficiently experienced to know how to handle VIP elements carefully.

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