Evaluation of vacuum insulation panels used in hybrid insulation district heating pipes

Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2014

It is of interest to lower the energy losses from district heating pipes both for economic and environmental reasons. This paper evaluates a hybrid insulation solution where Vacuum Insulation Panels (VIP) are put around the supply pipe in a district heating pipe and the rest of the casing pipe is filled with polyurethane foam (PUR). The apparatus for the “guarded hot pipe” method was used to estimate the thermal properties of single pipes, which have been used as input in finite element models for simulation of twin pipes in field. The simulations indicate a total reduction in the energy loss between 18% and 32% compared to pipes of the same size with pure PUR insulation. Furthermore, the losses from the supply pipe decrease by up to 56%. To achieve the low energy losses, the vacuum in the panels has to be preserved over the life span of the VIP. In field measurements, a hybrid pipe prototype was connected to the district heating grid in Varberg (southwest Sweden). After almost two years, the pipe is still working without any detectable deterioration of the insulation performance. The panels have also been tested at high temperatures in laboratory with promising results.