Optimisation of district heating transformation for the efficient integration of a low-temperature heat source

Reducing greenhouse gas emissions is becoming increasingly important, especially for energy systems that supply heat. District heating networks are a promising way to supply heat to buildings with low greenhouse gas emissions, especially with integrated low-temperature heat sources from renewables or waste heat. However, integrating low-temperature heat sources into existing district heating systems often requires a transformation to lower network temperatures. Promising approaches to reduce the network temperatures are the installation of central and decentral heat pumps and the refurbishment of the supplied buildings. In this paper, an optimisation model that considers refurbishment options for buildings and the installation of heat pumps to optimise the integration of low-temperature heat sources into existing district heating systems is presented. The presented methodology is applied to a real-world high-temperature district heating system. Compared to conventional waste heat integration with only a central heat pump, the consideration of optional decentral heat pumps reduces the total annualised cost by 6.4% and the additional consideration of building refurbishment options reduces the costs by 24.4%. Overall, the network temperatures at nominal supply could be reduced by about 50 K due to the adaptions made to the most critical buildings in the existing district heating system. The presented optimisation model shows the importance to also include decisions on building refurbishment in the overall district heating transformation process to achieve efficient integration of low-temperature heat sources.