Investigation on Relative Heat Losses and Gains of Heating and Cooling Networks

The integration of district heating (DH) and cooling (DC) in the sustainable energy system of the future requires a significant reduction in operating temperatures. Supply temperatures below 70 °C are required for new 4th Generation DH. Main benefits are the use of low exergy heat sources and the reduction of heat losses. The reduction of heat losses is achieved by reducing the driving temperature difference between the medium pipe and the ground. The decrease of the return temperature level is limited by the consumer behaviour and the ground temperature level. As a consequence, the reduction of the supply temperature is accompanied by a reduction of the maximum transmittable heat flow. For energy efficiency and economic reasons, the relative heat losses are therefore an important design value for DH networks. The study proposes an approach to estimate the relative heat losses by using steady-state heat loss models and analyses the values for different DH generations. In particular, due to the rising of the near-surface soil temperature, the relative cold losses are also studied.