Long-term thermal performance of vacuum insulation panels in district heating pipes: Nine years of field measurements

Paper i proceeding, 2025

Swedish district heating networks lose up to 10% of the produced energy through thermal transmission from distribution pipes. Vacuum insulation panels (VIPs) have attracted growing interest in the district heating sector due to their low thermal conductivity. Hybrid-insulated pipes, with VIPs applied around the steel supply pipe, have demonstrated heat loss reductions of up to 40% compared to conventional polyurethane insulation. However, their long-term performance under typical district heating operating temperatures (80-100 °C) remains insufficiently explored. This study presents field measurement results from two district heating networks in Sweden. In Varberg, a twin pipe system with VIP insulation was monitored for over nine years. In Linköping, a single pipe system was used to compare two types of VIPs, metallized and aluminum-coated, over seven years of operation. Measurements included supply and return temperatures as well as surface temperatures at multiple radial positions within the pipe cross-section. The results show that VIP-insulated sections consistently outperformed those insulated with conventional polyurethane, with temperature differences of up to 20%. In Varberg, a degradation rate of approximately 1.6% per year was observed in one measurement position, aligning with previously reported values from the initial four years of operation. In Linköping, metallized VIPs showed lower exterior insulation temperatures than aluminum-coated panels, indicating better overall thermal performance at the center of the panel. Although the temperature gap increased over time, the differences were minor and may reflect operational variability. Long-term performance differences could not be confirmed. Further research should investigate material-specific properties, including gas permeability and mechanical durability.