Bachelor's thesis Celia Burghardt

Evaluation of a district heating and cooling system using a LowEx-thermal network in combination with heat pumps

Studied district and layout of the thermal network Copyright: EBC Studied district and layout of the thermal network

The integration of renewable energies into the energy supply system is seen as one solution for achieving the national and international goal to reduce global warming. Focusing on the heat sector, a technology which is seen as having great potential for using a large proportion of renewable energies in buildings is district heating and cooling through thermal networks at low temperature levels. There are many design options for such kinds of networks, especially when it comes to choosing the temeprature level. Moreover, only few examples of this technology exist so far. Thus, it is difficult to identify the ideal supply temperature for specific applications of district heating and cooling. In this thesis, two thermal networks at different temperature levels are compared for the application of a planned district consisting of different residential buildings and a kindergarden. In particular, the concept of LowEx-thermal networks with variable temperatures below 40 C is compared to a conventional low-temperature network with a flow temperature of 70 C. The LowEx-network can be used for direct heating and cooling in buildings, but additional heat pumps are needed for producing domestic hot water. The sources of both networks are large-scale electrical heat pumps. The two networks are evaluated on energetic, ecological and economical aspects and compared to each other. The dynamic behaviour of the two energy supply systems is investigated in a dynamic simulation using the Modelica modelling language. The results of the simulation are used for the evaluation. Regarding energy efficiency, the LowEx-network is the better alternative: The total demand for electrical energy is significantly lower. This results in a lower primary energy factor for the district's heating and cooling supply via the LowEx network. In addition, the CO2 emissions of 185 g/kWh for the generated heat and cooling are way below the CO2 emissions of 453 g/kWh of the convencional low-temperature network and still below the average emissions of 280 g/kWh of district heating in Germany. Despite the higher investments for the LowEx-network in comparison to the conventional low-temperature network, caused e.g. by greater pipe diameters, it is found to be more economical. The main reason is the lower electricity demand of the large-scale heat pump.