It is becoming increasingly important that buildings are renovated, remodeled or constructed in an energy efficient manner. Vacuum insulation panel (VIP) materials are becoming important part in the field of insulation materials. They have been used for quite some time in the construction industries in colder areas, such as the Alps and Sweden. The insulating properties are achieved by sealing micro-fiber-based silica with a barrier film which is wrapped around it.
As vacuum insulation panels have a very low thermal conductivity compared to traditional building materials, they also have a high insulating effect relative to the low wall thickness. These properties can however cause a low heat flow. A greater measurement uncertainty is expected when determining the thermal conductivity, and this therefore reduces the confidence in the measurement results.
NETZSCH GHP 456 Titan® Guarded Hot Plate Instrument
Vacuum insulation panel thermal conductivity can be measured precisely and accurately using the guarded hot plate apparatus (GHP).
Measurements and Specimens
VIPs are evacuated insulation boards that have an insulation core such as silica powder, which is in an envelope that is impermeable to gas and water vapor (e.g. aluminum foil). The symmetrical design of the GHP needs two identical samples measuring 30 cm x 30 cm.
As the GHP is an absolute method, no calibration is needed prior to the actual measurement. Measurements were performed using the GHP 456 Titan® at 60°C, 23 °C, 0 °C, - 50 °C, -150 °C and -160 °C. To ensure reliable measurements with such low conducting specimens, a temperature difference (∆T) of 20 K and 10 K was used between the hot and cold plate. At very low temperatures a temperature difference of 30 K was used.
The measurements which are plotted in Figure 1 show that the VIP specimen’s thermal conductivity increases with increasing temperature. The thermal conductivity at room temperature is 1.85 mW/(m∙K). Values below 1 mW/(m∙K) were measured in the low temperature range.
Figure 1. Thermal conductivity of a VIP specimen between -160 °C and 60 °C
The results at various temperature differences (∆T) are in agreement, which proves the performance of the GHP 456 Titan® for ultra-low conducting material measurements. Even though there is very low heat flow, and a lack of flexibility in adjusting the parameters of the test, measurements can be carried out and evaluated correctly.
This information has been sourced, reviewed and adapted from materials provided by NETZSCH-Gerätebau GmbH.
For more information on this source, please visit NETZSCH-Gerätebau GmbH.