Heat networks for a more sustainable heat supply

The energy-intensive heating sector plays a decisive role in the energy transition and is a key factor in achieving climate targets. In addition to heat generation in the respective properties (decentralised heat generation), centralised heat generation and subsequent distribution along heating networks is another important pillar of our current heat supply system.

Compared to decentralised heating systems, centralised heat generation in conjunction with a heating network (district heating) is in general more efficient and can be a cost-effective alternative, particularly in densely populated urban areas. In contrast to decentralised technologies such as oil or gas heating systems, no heat generation is required in the respective property, meaning that there is no space requirement for a boiler. It is also possible to integrate waste heat sources or renewable heat sources such as geothermal energy, surface waters or waste water using large heat pumps. 

For this reason, district heating is of great importance for the current and future heat requirements of the existing and future building stock. Fraunhofer IFAM always endeavours to take a holistic approach: From the inclusion of the local and political framework to data processing as part of the analyses regarding the current status and further potentials, to the derivation of possible measures.  

The advantages of district heating and why heating networks are worthwhile

District heating networks have numerous advantages that are necessary for a sustainable heat supply. By increasing efficiency and using renewable energy sources to generate heat, CO₂ emissions in the heating sector can be reduced: a necessary contribution to climate neutrality. 

These advantages of district heating networks include:

• The use of (large-scale) heat pumps, solar thermal energy, combined heat and power generation based on renewable energy sources (biogas/ethanol, biomass, green hydrogen in the future) and existing, previously not utilised waste heat will enable the (gradual) integration of renewable energies. 

• Heat is supplied directly to the respective properties via the pipes installed, meaning that generally only one heat exchanger is required and installations such as a boiler, heat storage or possibly a fuel tank are not needed. There are also no exhaust emissions or fine particles on site, so chimneys and their maintenance are not required.  
• By lowering the temperature of the heat network, it is possible to increase the efficiency of heat generation and utilise renewable heat sources. Therefore the (gradually) switch to renewable energy sources can improve the carbon footprint of numerous properties in one go at comparatively low investment cost. The possibility of low-temperature district heating should be mentioned here in particular. 
• Due to the high number of consumers respectively large amount of heat extraction, the specific infrastructure costs remain low, even if the heat source is located further away, allowing for example open space solar thermal energy for sustainable heat supply outside residential areas.  
• Centralized heat generation can (gradually) switch to renewable energy sources at comparatively low investment costs and improve the carbon footprint of numerous properties in one go.  
• In inner-city areas with a high heat demand density, there are often restrictions when switching to renewable energies, as the required system size (e.g. for solar thermal energy) exceeds the available space or noise protection regulations (e.g. for heat pumps) prevent installation on site. 
• Enabling of sector coupling through large heat producers and heat storage: the implementation of large heat pumps, CHP units and large heat storage vessels is more economic than in small systems. The operation of these units can contribute to the balancing of fluctuating electricity production from renewable energy sources.

Heating networks must be economical - to analyse the potential is of enormous importance

In order to ensure the economic operation of heating networks, planning with regard to investment and operating costs is extremely important. The number of house connections and the possible volume of heat sales in relation to the necessary pipeline expansion in the supply area are decisive factors. 

Given the current restructuring of the heating market, analyses of potential are therefore of great importance. Fraunhofer IFAM provides support with a comprehensive suitability analysis at a spatial level using geographical information systems (GIS): 

• Analysis of the current situation and potentials: The current supply structure can be recorded based on location data of existing heating network infrastructures and decentralised supply structures as well as current heat requirements. Possible heating network expansion or new construction areas can be spatially identified along further heat source potentials.  
• Cluster: This spatial aggregation level differs from the administrative area categorisation and is central to determining the potential for heating networks. The respective project area is divided into areas with a similar settlement structure along separating infrastructures - separating infrastructures are main traffic arteries such as railway lines, motorways or rivers/canals, which regularly represent a boundary for network expansions. The information on heat demand, average heat line density, potential (renewable) heat sources, network expansion costs and existing heating networks is aggregated in the individual clusters. The overall view of the building structure, existing heat sources and sinks as well as existing heating infrastructures enables an evaluation of the potential for heating networks in these sub-areas. 
• Heat line densities: Specify the heat demand of the buildings adjacent to a street; the higher the heat line density, the higher the economic potential of a pipe-bound heat supply, as a high heat consumption volume can be tapped at low infrastructure costs.  
• Heat density: Is determined independently of the existing infrastructure along the building-specific heat requirements and can be used as an additional parameter for identifying areas with a high heat demand density. It can reveal a potential for smaller heating networks, as the pipe sections in small heating networks are often laid away from the street axes and the pipe installation costs are therefore lower than the heat line densities would suggest.  
• Possible utilisation of (waste) heat sources: The spatial location comparison of these sources with the heat sinks, and with the addition of the parameters described above, can be used to increase the potential of existing heating networks or as a basis for the construction of new networks.

The analyses carried out meet the requirements of the municipal heat planning legislation, both with regard to the analysis of the current situation, in which the existing supply structure is recorded, and with regard to the analyses of heat potentials. A key element of the latter is the zoning of the study area, which considers both the decentralised supply and the grid-based heat supply. Our experts process this geographical data together with information on infrastructure costs and possible subsidies. In this way, future potentials can also be determined, taking into account current political measures and concepts. Based on the results, a target scenario can be developed with regard to climate neutrality, and from this a heat transition strategy can be developed and recommendations for its implementation can be given.

Prospects for a sustainable heat supply

The Energy System Analysis research team considers the grid-based heat supply to be one of the central technologies for a secure and sustainable way of providing heat. By considering renewable heat sources and having the energy efficiency of the overall energy system in mind, a contribution can be made to achieving climate protection targets. With their holistic and competent approach to the topic, our experts provide long-term support in making the heat supply more sustainable.