Influence of supply temperature and booster technology on the energetic performance of a district heating network

In 2019, 70% of the households in Flanders still used natural gas as a fuel for space heating. To accelerate the decarbonisation of the building stock in urban areas, district heating networks supplied by a central heat pump in combination with geothermal energy, were suggested. While central heat pumps are more energy efficient at low condensing temperatures, existing buildings often require high supply temperatures for space heating and domestic hot water. In addition, heat losses decrease when lowering the supply temperature in the distribution network, while pumping losses can simultaneously increase due to increased mass flow rates. This article investigates the influence of low and ultra-low supply temperatures on the primary energy demand and energy efficiency of a district heating network supplied by a central heat pump, taking into account the need for booster heat pumps or booster electric heaters. The simulations consider network temperatures ranging from 10°C to 75°C and distinguish between refurbished and non-refurbished buildings. The dynamic simulation of the network is performed using the IDEAS and Buildings libraries in Dymola (Modelica). The results indicate that the most energy-efficient scenario is to keep the network at ground temperature and locally boost the water to the desired temperature. Booster heat pumps show a lower energy consumption compared to booster electric heaters, but have a higher investment cost. Refurbished buildings profit from the district heating network at ground temperature, reducing the primary energy consumption without the need for individual geothermal boreholes. For non-refurbished buildings, a higher 358 network temperature might be chosen over an ultra-low network temperature to avoid high investment costs for the end-user for refurbishment and booster heat pumps. Keywords: District heating, space heating, domestic hot water, energy efficiency, energy system analysis, Modelica, booster heat pump