District heating in areas with low energy houses - Detailed analysis of district heating systems based on low temperature operation and use of renewable energy
Technical University of Denmark, PhD Thesis, (2015)Abstract
The Danish energy scheme aims at the use of renewable energy for the heating of all buildings by 2035. A new generation of district heating systems operating at low temperatures and employing renewable energy sources is seen as being able to accomplish this. The intention is to integrate low-temperature district heating systems operating at very low temperatures, such as 55°C for supply and 25°C for return. The basic aim of the PhD project reported on here was to find optimal solutions to this involving use of renewable-energy-based low-temperature district heating systems at the municipal and the regional level. The detailed analysis of several cases, each representing a unique infrastructural municipal heating task, can provide a rational basis for innovative transformations and developments in adapting whole regions to the use of the low-temperature district heating systems. Attention is also directed at intensive efforts that have been directed at a comprehensive integration of renewable energy sources in meeting the energy requirements of portions of the Danish energy supply, research questions there being formulated in terms of efforts to solve two major tasks: (i) the proper dimensioning of district heating networks and (ii) the economic exploitation of locally-available renewable energy sources, as examined in three case studies, each being carried out in collaboration with Danish municipalities.
The first case study, conducted in collaboration with Roskilde Municipality, was concerned with the designing of low-temperature DH networks for new settlements, for which the building of low-energy houses was planned, in particular matters of the network dimensioning method to be employed, the substation type, the network layout, and the hydrostatic pressure level that was best considered. The second case study, carried out in collaboration with Gladsaxe Municipality, was directed at replacing existing heating infrastructures, such as natural gas grids and high-temperature district heating systems, with low-temperature district heating systems for the existing areas, in which it is planned that the houses presently located there will be renovated so as to achieve a high degree of energy savings. The third case study involved research question aimed at investigating possibilities of exploiting the locally available non-fossil fuel sources to be supplied to low-energy district heating systems.