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From 3G to 5G District Heating and Cooling networks (energy generation to substations)


The new generation of district heating and cooling networks are based on low and/or ultra-low temperature sources of renewable energy and waste heat for heating as well as high-temperature cooling. Such networks provide key options for decarbonizing the thermal energy needs of the building sector and allow supporting strategies for climate neutrality in the urban context for reaching net-zero greenhouse gas emissions while increasing energy security. This factsheet aims to provide knowledge, information, and recommendations on advancing district heating and cooling networks into the new generation based on low and/or ultra-low temperature district heating solutions. The factsheet provides perspectives on establishing the complete network from energy generation to substations toward climate neutrality in urban areas. 
Each successive generation of district heating and/or cooling technologies has involved an improvement in supply temperatures and efficiencies. For heating, whereas the current generation of third generation (3G) district heating networks involves supply temperatures at 100°C and below, distribution efficiencies and grid losses are further improved in the newer generation of fourth (4G) or fifth generation (5G) networks. The common point of such networks is the utilisation of locally available renewable energy sources at temperature levels as close to the actual demand temperature for heating and cooling of connected end-users as possible. There are both similarities and differences between these networks and relevant technologies can co-exist. In the more well-established 4G definition, supply temperatures are a maximum of about 60°C for heating and below [1]. As a subcategory concept, depending on definition, bi-directional ultra-low temperature district heating with supply temperatures at 50°C and below are also used to refer to 5G networks [1]. Some networks operate at near-ambient and ambient temperatures with different network-substation configurations. For district heating and cooling networks operating at 10-30°C , thermal grid losses can be about two-thirds less over 3G networks while requiring extra electrical energy for driving the pumps in the network distribution and substations [2].    


Overall, the new generation of district heating and cooling networks is contextualised within smart energy systems where smart thermal grids support higher penetrations of renewable energy sources in the energy system [3]. Smart thermal grids also include large-scale heat pumps that are powered by excess renewable power from intermittent energy sources of solar and wind that would otherwise be curtailed [4]. The ability to integrate low and/or ultra-low temperature renewables and waste heat from multiple sources with or without booster heat pumps defines a central aspect of the new generation of district heating and cooling networks (also see Figure 1 and a complementary factsheet on “Technologies and applications for low/high temperature heat recovery in district heating”). In addition, the new generation of district heating and cooling networks require buildings that are compatible with using low or ultra-low temperature district heating and high-temperature district cooling. This will require building renovation, if not sufficiently compatible, or booster heat pumps. Locally, solutions can be directed to also addressing energy poverty in the urban context and raising thermal comfort. Seasonal thermal storage can support the performance of new generation district heating and cooling networks, including aquifer or borehole thermal energy storage that can provide long-term thermal energy storage [1]

Figure 1. Generations of district heating and cooling networks with 4G covering both low and ultra-low temperature district heating networks. Low-temperature refers to supply temperatures of about 50-60°C and maximum of 70°C for heating. Ultra-low temperature refers to supply temperatures below 50°C for heating, overlapping with 5G networks [1]. Two options that relate to another solution factsheet for heat recovery from data centers and supermarkets are marked.   

Technically, different configurations of district heating and cooling networks can lead to different efficiencies, flexibilities, and integration of renewable energy and waste energy sources [5]. As a representative comparison, Table 1 provides an overview of the typical technical specifications for district heating and cooling networks that are labelled as 5G. For example, some have both central and distributed designs for the shared thermal source operating at fixed or variable system temperatures and single and/or two pipe distribution systems with or without pipe insulation and thermal storages. It is common for heat pumps to be placed in substations or the side of end-users in buildings with prosumers. This can minimize upfront investment cost for utilities while potentially increasing the initial investment for the end-users. 

New generation district heating and cooling networks are envisioned to be more flexible in the way energy is exchanged, not relying on the central provision of heat and cold in part or whole, and with diverse connections to the network. A much more specialised form of new generation district heating and cooling networks is defined based on thermal energy supply grids using water or brine as a carrier medium that operates at temperatures close to the ground temperature and is supported by hybrid substations and water source heat pumps [6]. Yet different definitions for the same concept can often overlap, including bi-directional low temperature networks and even anergy networks [6].  Networks can also involve free-floating network temperatures with bi-directional and decentralised energy flows and active substations with prosumers. 


Table 1. Technical specifications of district heating and cooling networks labelled with the 5G concept (adapted from [1]

Supply Tempera- ture ( T ) 

Shared thermal source design 

Distribution system 

Pipe insulation 

System temperatures 

Thermal storages 





Single pipe 

Two pipe 

≥ Three pipes 





Short term 

Long term 

T < 50°C 

























































T < 40°C 







































































































T < 30°C 



































































































































































































































































































































Ground Temperature 
























































































































































































































Figure 2. Zoomed-in urban area as an example of the heat demand densities mapped across Europe in the Pan-European Thermal Atlas (Peta) [29]. The new generation of district heating and cooling networks will be developing in these contexts.  

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