Spatial Heat Planning and Heat Demand Reductions in Buildings

In recent years, great attention has been paid to renewable energy systems both at a local and national level. This interest on renewable energy sys-tems is mainly due to an increased acceptance that climate change is an-thropogenic and directly related to the use of fossil resources. Changing over to an energy system based 100% on renewable energy is not just a fi-ne-tuning of the existing system, but is a fundamental change of the entire energy system. However, similar to the use of fossil fuels, biomass re-sources, which account of a large share of the renewable energy sources, are limited in relation to their sustainability. In order to use biomass re-sources in a sustainable manner, their use must be minimised by increas-ing the efficiency in the energy system and reducing the end-use consump-tion. Other types of renewable energy, such as wind and solar, are sustain-able but geographic limitations and their fluctuating energy production gives other challenges. To be able to use such renewable resources it is necessary to increase the flexibility of both the energy system and the end-use consumption.

This PhD thesis involves topics related to the transition towards 100% re-newable energy with a main focus on the heat supply in Denmark. Even though the focus is on Denmark, the methods and results are applicable to other places as well, as they build on assumptions that are also present in other countries. In Denmark approximately half of the heat demand is sup-plied by district heating, and half of the district heating already uses renew-able energy. Within densely built-up areas district heating systems are re-source effective compared to individual solutions as district heating sys-tems can use excess heat from power plants, industries, and waste incin-eration as well as renewable energy, like geothermal and large solar collec-tors, resources which are inaccessible to individual households. District heating systems also help integrate renewable energy production fluctua-tions through large heat pumps and heat storages. Therefore, district heat-ing is often seen as an important part of 100% renewable energy systems.
The goal of the thesis is to examine the following questions: 1) Is renewable energy production from buildings useful in district heating areas? 2) What benefits are related to heat savings in buildings within district heating are-as? 3) How do geographic differences in heat consumption and supply in-fluence the expansion possibilities of district heating? These questions are examined by establishing different models that focus on both temporal and spatial differences. The primary focus of the first part of the thesis is on the use of solar heating from buildings in general types of district heating are-as. This is followed in the second part by a case study which examines heat savings in buildings. The primary focus of the third part of the thesis is on the geographic aspects of district heating and develops geographic models for district heating expansion potentials and uses them in analyses.

In general geographic placement of buildings, and hereby their heat de-mands, is an important factor when choosing the best heat supply option. The heat supply decision should be based on larger coherent areas of build-ings because the benefits of district heating are only found when whole sys-tems are examined instead of individual buildings. Another challenge dis-cussed in this thesis is how to reduce the heat demand in buildings within district heating areas as the consumer price often does not reflect the long-term costs of heat production. The analyses show that heat savings results in considerable long-term savings in investments in production capacity and fuel costs. Through a case study, the amount of these long-term sav-ings is compared to the costs of implementing heat savings. The case study shows that heat reductions of roughly 50% are feasible if the long-term costs are included. Savings of 75% are less feasible. In general the conclu-sions on rates of savings are based on which heat supply exists in each dis-trict heating area; in areas with expensive heat production the heat savings will be more feasible than in less expensive areas.

New geographic models have also been developed in this thesis with the aim of finding the costs of district heating expansion compared to the costs of individual solutions. With the help of these models, it is found that dis-trict heating expansion is still possible in Denmark. The potential is reduced if significant heat savings are introduced in the building stock. This conclu-sion is based on analysing the existing systems, and therefore, it is im-portant to improve the district heating systems by increasing the efficiency of the systems as well as minimising the heat loss on the grids. In the geo-graphic modelling of district heating system expansions, it is important to distinguish between production, distribution and transmission costs. Differ-entiating between these factors ensures that geographic differences in heat density and distance between areas are included. In the models of distribu-tion networks, it is important to include the geographic placement of build-ings within each area. When calculating the transmission costs, it is im-portant to consider that more than one area can use the same connection, minimising both the costs and the heat loss in the network.

It is clear that both temporal and spatial tools are required in the future when 100% renewable energy plans is developed. It is essential that both dimensions are includes, as this is the basis for finding the best solutions in a sustainable way. Both methods contribute with important knowledge in regards to the usage and integration of renewable energy.