- Erik Rundgren, Eric Nyberg. 2014. Värmeförluster vid relining inom fjärrvärme. Abstract: The replacement of old pipes for district heating is signified by high expenses. Traditionally, this includes major costs in terms of personnel and resources, but also in terms of collateral costs such as disruptions in traffic and the urban surroundings. By restoring the old pipes, instead of replacing them, the network owners hope to be able to carry out the renewal of the network pipes faster, at reduced costs and with less damage to the environment.Relining is pipe renewal. Relining has been used when restoring sewage pipes for several decades and, for the last twenty years, also when restoring drinking water pipes. Until now, district heating pipes have not been subject to relining. District heating pipes, unlike sewage pipes, are exposed to tough conditions in terms of both pressure and temperature. The conditions in the district heating pipe system and the limitations in the available materials have until now hindered the market for restoring these pipes. During 2013, a study was conducted on relining with a composition of modern plastics and fiber materials. The outcome of that study was that relining companies as well as potential customers noted that modern techniques and materials have the potential of managing the changes in temperature and pressure that the pipes in the district heating system are exposed to.There are still several unanalyzed aspects of restoring district heating pipes. Because of the lack of commercial products in the field, multiple parameters are missing for calculating the profitability of investments in pipe renewal through relining. One of the aspects is the potential differences in heat loss between relined old pipes and new modern pipes. These differences may affect the variable costs for the distributors of district heating.This study aims to present an estimate of the magnitude of the differences in heat loss caused by relining as a substitute to replacement of old pipes. The heat loss was calculated for a case study with multiple cases, where different circumstances apply in the system.The study concludes that the heat loss from relined pipes may be prominently larger in cases where the insulating materials around the pipe have degenerated. If the insulation consists of wet mineral wool, there is a risk of doubling the heat loss from a relined pipe in comparison with the heat loss from a new pipe. Also, the calculations show that relining of pipes, embedded in an undamaged culvert, contribute very small differences in the heat loss. The condition of the pipe network should be subject to consideration when making investment calculations for renewal of the district heating system.Insufficient knowledge of the condition of the pipes may lead to application of a lesser method for renewal of the system. In terms of heat loss, it may cause major costs for distributors of district heating.
