Case Study of a Low-Energy District Heating Network in Energy-Efficient Settlements in Denmark

The decreased heating demand in low-energy buildings affects the cost-effectiveness of traditionally-designed district heating (DH) systems. This paper presents the innovative low-energy DH concept, which is based on low-temperature operation. The annual energy performance of a low-energy network for low-energy houses in Denmark was investigated. We considered the influence of the human behavior on the energy demand, the importance of the degree of buildings connected to the network and a socio-economical comparison with ground source heat pumps. In the North European climate, the human behavior can lead to 50% higher heating demand and 60% higher heating power than expected according to reference values in standardized calculation of energy demand pattern in energy-efficient buildings. Next, we proved that low-energy DH systems are robust systems that ensure the security of supply to each customer in a cost-effective and environmentally friendly way in areas with linear heat density down to 0.20 MWh/(m.year). This suggests that the mandatory connection of low-energy buildings to DH in specific areas, by means of detailed energy planning, would improve the energy efficiency and the overall socio-economy and it is strategic for effective energy policy. The levelised cost of energy in case of low-energy DH supply is competitive with the scenario based on ground source heat pumps. The investment costs represent up to three quarters of the overall expenditure, over a time horizon of 30 years; hence, the implementation of an energy system that fully relies on renewable energy needs substantial capital investment, which in the long-term period is sustainable, from the environment and socio-economical point of views. The low-energy district heating concept fits the vision of the future energy sustainable society.