District heating (DH) will play an important role in the future fossil-free energy systems by enabling increased utilization of waste heat and renewable heat sources to cover buildings' heat demand. A prerequisite for this is a reduction in the distribution temperature and shift towards decentralized heat production. In this study, dynamic modeling has been applied to study the technical, energetic and environmental impacts of including prosumerscustomers who both consume and produce heat -in a local low-temperature DH grid. Four different scenarios were studied for a planned building area in Trondheim, Norway: high-and low-temperature scenarios with the entire heat demand being covered by a heat central, and two low-temperature scenarios including heat supply from prosumers. A data center and two food retail stores were considered as the prosumers, each with different location and individual characteristics for the heat supply, allowing to study their impact on the water flow in different parts of the grid. The results show that utilizing local surplus heat is a significant measure to reduce the heat demand and the environmental impact of the DH grid. Decentralized heat supply additionally contributes to reduced heat losses, due to overall lower distances to transport the heat.

Today's district heating (DH) networks in Norway are 2nd and 3rd generation systems, with supply temperatures ranging from 80-120 • C. In new developments, it is desirable to shift to 4th generation, low-temperature district heating (LTHD) in order to reduce the heat losses and enable better utilization of renewable and waste heat sources. A local LTDH grid for a new development planned in Trondheim, Norway, has been modelled in the dynamic simulation program Dymola in order to study the effect of lowered supply temperatures to heat losses and circulation pump energy use. Different cases with supply temperatures ranging from 55 to 95 • C, lowered return temperature as well as peak shaving were analyzed. Real DH use data for buildings in Trondheim were employed. The environmental impact in terms of the total produced CO 2 equivalent emissions was estimated for each case, assuming a heat production mix corresponding to that of the local DH provider. The results showed that by lowering the supply temperature to 55 • C, the heat losses could be reduced by one third. The total pump energy increased significantly with reduced supply temperature, however the pump energy was generally an order of magnitude lower than the heat losses.

No abstract

Modern building complexes have simultaneous heating and cooling demands. Therefore, integrated energy systems with heat pumps and long-term thermal storage are a promising solution. An integrated heating and cooling system for a building complex in Oslo, Norway was analyzed in this study. The main components of the system were heat pumps, solar thermal collectors, storage tanks, ice thermal energy storage, and borehole thermal energy storage. Dynamic simulation models were developed in Modelica with focus on the long-term thermal energy storage. One year measurement data was used to calibrate the system model and two COPs were defined to evaluate system performance. The simulation results showed that more heat had to be extracted from the long-term thermal storage during winter than could be injected during summer. This imbalance led to a decrease in ground temperature (3 °C after 5 years) and decreasing long-term performance of the system: both COPs decreased by 10 % within five years. This performance decrease could be avoided by increasing the number of solar collectors from 140 to 830 or by importing more heat from the local district heating system. Both measures led to sustainable operation with a balanced long-term thermal storage.

No abstract