Long term performance of vacuum insulation panels in hybrid insulation district heating pipes

This paper presents studies on district heating pipes where a vacuum insulation panel replace the innermost layers of polyurethane around the service pipe. One of the main challenges are their long term performance. Prototypes have been tested both in field in a district heating grid and in laboratory with a constant temperatures. The results indicate that the panels are intact after four years in field. In the laboratory, the pipes have been exposed to a constant temperature of 115°C for over three years without damage to the panels.