Evolution of Future Heating Systems - Modeling of an Expanding City Using a Dynamic Systems Approach

Doctoral thesis, 2023

Reducing greenhouse gas emissions is central to meeting climate change mitigation targets. Since the energy sector is one of the largest greenhouse gas emitters, it is essential that all the actors within the energy sector reduce their respective emissions. The heating sector is an important component of the larger energy system, especially in the Nordic countries. In the Nordic region as a whole, a large part of the heating demand, both from hot tap-water and space heating, is covered by district heating (DH), especially in cities. In less-densely populated areas, the use of individual heating solutions is more common, although individual solutions are present also in urban areas. The economic viability of an individual solution is, therefore, dependent upon the geographic placement, as well as the surrounding system. How the transformation of existing heating systems into future carbon-neutral systems can be achieved is of great interest.

The components of heating systems often have very long lifetimes, and given the urgency of phasing out fossil fuels, the constitutions of future heating will reflect decisions made in the near future. As there are high levels of uncertainty associated with several factors involved in the development of heating systems, the aim of this thesis is to investigate how different parts of the heating system can be developed in parallel and to maximal efficiency in different future scenarios.

A dynamic systems approach is used in which the supply and demand of an expanding heating system are investigated together and simultaneously over several decades. New housing is treated in a heterogeneous fashion by investigating several types of new housing. The cost-optimizing TIMES modeling framework is used in this thesis, and the heating system of Gothenburg is applied as a modeling case.

The modeling results show that the heating solution for future housing depends on the housing type and the construction year. Individual solutions, mainly ground-source and air-to-water heat pumps, are often cost-efficient for single family housing, as well as for apartment buildings. This is especially the case if the electricity price is low or if the use of biomass in the DH system is phased out. However, the utilization of low-grade excess heat or a lower DH temperature increases the use of DH in the future housing stock. Large-scale seasonal thermal energy storage units in DH systems are economically viable systems that, in some cases, can increase the use of DH for new housing, although the effect is rather weak. Nevertheless, storage systems can significantly reduce the strain on electrical grids during cold periods.

The choice of heating solution represents a serious challenge for the economics of DH systems, which have traditionally been the main heating solution in cities. The development of current DH systems has been incremental in the recent decades, while individual solutions have undergone a dramatic increase in their use. Without more-drastic changes in the investment in and operation of DH systems, the heating systems of the future may become more-decentralized and more-dependent upon electricity as their main energy source.

The findings of this thesis should be of interest to city planners and DH utilities, as the findings show that both the DH supply side and the heating solution for new housing are affected by many factors.