Assessing the Thermal Performance of District Heating Twin Pipes with Vacuum Insulation Panels

In Sweden, around 10% of the energy supplied to the district heating networks are lost through heat losses from the distribution pipes. In cylindrical geometries it is preferable to improve the insulation as close to the center as possible. This has resulted in a hybrid insulation district heating pipe concept with a combination of vacuum insulation panels at the center, held in place by polyurethane foam. In the twin pipe concept, the vacuum insulation panel cover the supply pipe. This creates a complex temperature profile over the section and measured results on single pipes might not be applicable. Therefore, there is a need for a method to evaluate the improvement of hybrid insulation twin pipes in the laboratory. This paper presents a method where two guarded hot pipe apparatuses is used, one heating rod for each pipe, to measure the heat losses from hybrid pipes and compare to a conventional polyurethane pipe. The measurements indicate an improvement in thermal performance by 12%-18% for the total losses and by 29% -39% for the supply pipe losses.