Future District Heating Interactions – Modelling Impacts of Industrial Excess Heat Utilisation and Energy Efficient Buildings

Doctoral thesis, 2018

International goals for climate change mitigation plus energy security targets could be met cost-effectively by interactions between different parts of energy systems. The fourth generation of the district heating systems concept was developed as an attempt to accelerate district heating (DH) systems’ interactions with other energy systems. This thesis investigates future interactions of district heating (DH) systems with industries and buildings. This is investigated by developing a methodology and applying it to real cases.

Taking a long-term and system-wide perspective, the investigation includes carbon (CO2) and techno-economic impacts of increased energy efficiency in industries and buildings on the DH systems. Real case studies are selected to capture the local conditions of DH systems. Climate policy scenarios are designed as the starting point for the investigations and systematic sensitivity analyses are designed to test the robustness of the case study results. The tool applied is dynamic energy systems optimisation modelling. A regional MARKAL model is applied for DH-industry interactions, whereas a local TIMES model is applied for DH-building interactions. The heating sector and parts of the electricity, transport, industry and building sectors are represented in the optimisation models.  

The results show that, through a large heat network allowing for long transmission of industrial excess heat (EH) to DH systems, the DH-industry interaction requires major investment. Such investment is likely to be profitable if the EH replaces DH (which is primarily supplied by costly primary energy sources). From a systems perspective, the investment is less likely to be profitable if other EH sources contribute a large share of the DH base load and if there is an abundance of locally available, low-cost biomass. If built, heat networks help reduce biomass and fossil fuel use and provide a related reduction in CO2 emissions in DH systems. This outcome implies decreased electricity generation from combined heat and power (CHP) plants, in the region studied.

In low-energy building (LEB) areas, DH-building interactions (using a heat connection which allows heat to be supplied from a nearby urban area DH system to an LEB area) are cost-effective relative to local (on-site) DH and individual heat supply options. However, changes in energy flows (and CO2 emissions resulting from the nearby urban area DH systems) depend on assumptions about future climate policies, marginal electricity generation and alternative use of biomass, as well as the scale of the urban area DH system.