The reduction of heat losses is a key issue for the efficient use of energy. The use of insulating materials is one of the most effective measures to reduce heat losses. The quality of insulating materials, e.g. their thermal conductivity, is therefore critical for the ecological and economical operation of buildings and in industry.
The thermal conductivity of insulating materials and therefore the heat loss rate is influenced by temperature and moisture.
There are different methods to determine the thermal conductivity of insulating materials. IGTE use the “method of two-plate apparatus”. The thermal conductivity is measured as per the following two standards:
- DIN EN 12664: Thermal performance of building materials and products - Determination of thermal resistance by means of guarded hot plate and heat flow meter methods - Dry and moist products with medium and low thermal resistance; German version EN 12664:2001
- DIN EN 12667: Thermal performance of building materials and products - Determination of thermal resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium thermal resistance; German version EN 12667:2001.
Method of two-plate apparatus
In the two-plate apparatus, two samples which are as identical as possible regarding their materials and dimensions, are installed in the middle between two cooling plates (top and bottom) and an electrical heating plate. A heat flow is generated and determined by defined temperature differences between heating plate and cooling plate.
The heating plate in the middle consists of a central heating plate (measuring section) and is surrounded by a protective heating ring (protective ring section). The protective heating ring, along with the surrounding thermal insulation materials, results in a lateral heat flow reduction and therefore an improved measuring accuracy. The system is controlled in such a way that there is the same constant temperature difference both at the upper and the lower sample.
Sample medium temperature 10 – 95 °C
Temperature difference between heating plate and cooling plate: 2 - 20 K
Thermal conductivity 0.002 – 1.5 W/(m K)
Specification of samples
The minimum dimensions of the samples are 500 mm x 500 mm (length x breadth); the maximum dimensions are 900 mm x 900 mm. The thickness of the sample depends on its thermal conductivity. Depending on the thickness of the sample (at least 40 mm; 160 mm at most), its thermal conductivity between 0.002 W/(m K) and 1.5 W/(m K) can be determined.