MODELING ENERGY LOSSES AND GAINS IN LOW TEMPERATURE BI-DIRECTIONAL HEATING AND COOLING GRIDS A CASE STUDY OF E.ON’S ECTOGRID

Abstract: Energy for heating and cooling purposes is essential for many industrial processes, as well as something we all rely on to provide us with warm water and a pleasant indoor climate. As much as half of all energy consumed in the EU is used for heating and cooling [1]. District heating and cooling grids are common ways in which the energy is delivered and distributed, and due to the large quantities of energy in the systems it is of importance that the efficiency is high. One way to optimize the grids are by minimizing the energy losses of the pipes. In conventional district heating the pipes are insulated and losses are always negative, and many models have been developed to predict and calculate these losses. This thesis analyses the energy gains and losses on the 5th generation district heating and cooling grid, E.ON ectogridTM. Since the models on energy losses in conventional district heating or district cooling are not applicable for this type of 5th generation uninsulated grids with low temperature and bi-directional flows, this thesis attempts to find other ways of quantify and predict the energy-losses. The approach is primar- ily data-driven, by calculating and modeling the energy gains and losses based on empirical data collected from an ectogridTM. In developing a model, the energy losses were studied separately for the warm and the cold pipe of the grid. The temperature changes of the water in the pipes were also studied. The results suggest that energy loss varies based on energy demand, temperature of the pipe and its surroundings, and the grid layout. There are primarily energy losses from the warm pipe, which is expected as the temperature of this pipe is typically warmer than the outside temperature. The cold pipe experienced gains in cooling energy during the winter, but losses during the summers when cooling is needed the most. The implications of these losses are analysed, in regards to how they relate to grid design, and when losses are actually beneficial to the system. Based on the findings of the temperature change on the pipes, the warm pipe heats up the cold pipe, and the cold pipe cools the warm pipe more than expected. For more energy efficient grids it is suggested to add insulation to the warm pipe or separate the pipes. Energy losses might be further reduced if the temperature difference between the pipes is smaller. One of the most significant findings was that some of the data collected from the ectogridTM proved to have large variance and was unreliable, introducing a lot of uncertainty into the models. For further studies it is therefore recommended that more sensors are installed on the grid.