A novel freeze protection strategy for shallow buried sewer pipes: temperature modelling and field investigation

The burial of sewer and water pipes below the maximum ground frost depth can be very costly and laborious in regions with cold winters. If a freeze protection measure is applied, the utility lines can be installed in a shallower trench to reduce the excavation needs. One freeze protection measure, so called heat tracing, consists of supplying heat along the pipes. In this work, the use of 4th generation district heating as a heat tracing solution was investigated at a pilot site in Kiruna, Sweden. The influence of the system on sewer and water pipe temperatures was studied at a snow-free and snow-covered cross section. To this end, five heat tracing temperatures were tested and the corresponding sewer and water pipe temperatures were measured. The field experiment was also simulated with a two dimensional finite volume model. The study showed that, under the climatic conditions of the experiment, a heat tracing temperature of 25 °C allowed prevention of freezing of the pipes while keeping drinking water pipes in a safe temperature range at both cross sections. The other main result was that the developed finite volume model of the sections showed a good fitting to the experimental data.