Al-foil-bonded enveloping and double enveloping for application to vacuum insulation panels

• Two enveloping methods are examined.
• Al-foil-bonded enveloping method can improve the service lifetime of the VIP.
• Double enveloping can guarantee longer service lifetime and less edge conduction.

Two enveloping methods of vacuum insulation panels (VIPs) to enhance the service lifetime and reduce the degree of edge conduction are analyzed: Al-foil-bonded enveloping and double enveloping. In the first method, Al-foil is bonded onto the outer or inner surface of an Al-metallized film envelope except at the edge. The gas permeation rate is analytically found to decrease to virtually zero in the Al-foil-bonded region without any increase of the edge conduction. The double enveloping is to envelop a completed VIP once again with an additional buffer volume. This method is studied for the service lifetime, thermal conductivity at the center, and edge conduction. It shows significantly increased service lifetime compared with case of single enveloping with Al-metallized film and decreased overall effective thermal conductivity compared with a single enveloping using Al-foil film. These two enveloping methods ensure increased service lifetime and reduced edge conduction for practical applications.