Mikael Risberg

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.

Investigation of thermal indoor climate for a passive house in a sub-Arctic region using computational fluid dynamics

There is currently an increasing trend in Europe to build passive houses. In order to reduce the cost of installation, an air-heating system may be an interesting alternative. Heat supplied through ventilation ducts located at the ceiling was studied with computational fluid dynamics technique. The purpose was to illustrate the thermal indoor climate of the building. To validate the performed simulations, measurements were carried out in several rooms of the building. Furthermore, this study investigated if a designed passive house located above the Arctic Circle could fulfil heat requirements for a Swedish passive house standard. Our results show a heat loss factor of 18.8 W/m2 floor area and an annual specific energy use of 67.9 kWh/m2 floor area, would fulfils the criteria. Validation of simulations through measurements shows good agreement with simulations if the thermal inertia of the building was considered. Calculation of heat losses from a building with a backward weighted moving average outdoor temperature produced correct prediction of the heat losses. To describe the indoor thermal climate correctly, the entire volume needs to be considered, not only one point, which normally is obtained with building simulation software. The supply airflow must carefully be considered to fulfil a good indoor climate.