5th Generation District Heating: Existing Cases in Europe

We are happy to present to you the third issue of our heatbeat Research Newsletter. While the last two issues focused on 4th generation heating networks and the demand side (domestic hot water generation), we are now looking at 5th generation district heating and cooling networks. Especially the integration of waste heat and renewable energies is promising in these kind of systems. The selected paper gives an overview of the technology, differentiates these new types of heating networks from others and discusses examples of networks in operation in Europe.

The short version

We dedicate our third issue to the paper 5th generation district heating and cooling systems: A review of existing cases in Europe by Simone Buffa et. al. The paper is a cooperation between EURAC Research (Institute for Renewable Energy) and the Faculty of Science and Technology of the Free University of Bolzano. It examines and classifies modern heating networks. The authors note that the networks studied are different from those of the 4th generation and therefore propose the classification "5th generation heating and cooling networks". Key features are

• the energy is distributed at low temperature levels and is not suitable for direct heating
• decentralized heat pumps are used in the buildings with the thermal network as a low temperature heat source
• the heat supply integrates waste heat and renewable energies at low temperatures
• the same infrastructure is used for heating and cooling.

A total of 40 networks in operation are studied and analyzed in detail. Most of the networks are located in Switzerland and Germany with 15 sites identified in each country.

The paper provides a comprehensive overview of 5th generation heating and cooling networks and their application. Fifth generation heating and cooling networks are currently a highly discussed topic. The authors highlight the opportunities and benefits based on 40 existing networks studied, but also point out future challenges. The systems offer the possibility to use waste heat and renewable energies in the heat supply, which cannot be used in conventional networks. In addition, they enable simultaneous heating and cooling and offer a large potential for sector coupling. The challenges include the more complex planning and operation of the heat networks as well as new business models that compensate for the high initial investments and win the trust of customers in these networks.

Our full summary

The paper 5th generation district heating and cooling systems: A review of existing cases in Europe by Simone Buffa et. al. characterizes a new form of heating and cooling networks by examining 40 modern thermal networks. The paper is a cooperation between EURAC Research (Institute for Renewable Energy) and the Faculty of Science and Technology of the Free University of Bolzano.

In the last ten years, there has been a significant increase in the installation of 5th generation heating and cooling networks. The authors attribute this, among other things, to the fact that the cooling demand in buildings is growing and can be covered simultaneously with the heating demand using the same pipelines. In fact, in this kind of thermal network, buildings have the chance to become prosumers (i.e. to be heat consumers and producers at the same time). The authors define 5th generation heating and cooling networks as a new type of concept, which differs from 4th generation heating networks especially in the following aspects:

• the energy is distributed at low temperature levels and is not suitable for direct heating
• decentralized heat pumps are used in the buildings with the thermal network as a low temperature heat source
• the heat supply integrates waste heat and renewable energies at low temperatures
• the same infrastructure is used for heating and cooling

One focus of the authors is on the energy and mass flows in the thermal network. A distinction is made between unidirectional and bidirectional energy flows as well as between directed and undirected mass flows. For 5th generation heating and cooling networks, a bidirectional energy flow is particularly important, which means that connected buildings in the network can be heated and cooled at the same time. Networks with directed and undirected mass flows differ in the use of centralized or decentralized pumps.

The paper lists strengths and opportunities as well as weaknesses and threats for the use of the 5th generation district heating and cooling networks as the results of a SWOT analysis. Strengths of the concept are that almost all heat flows can be used regardless of their temperature level and the distribution at low temperature level enables a bidirectional operation. Furthermore, the network can be used simultaneously for heating and cooling purposes. Due to the small difference between the ground temperature and the network temperature, heat losses can almost be neglected, and thus cheaper uninsulated plastic pipes can be used. These advantages give utilities the opportunity to develop new business models (adjustment of power and operating prices, pricing of waste heat, etc.), which lead to a stronger interaction with the customer and the electrical network (use of heat pumps, direct use of PV electricity). The integration of waste heat and renewable energies facilitates the decarbonization of the heating sector.

The strengths and opportunities are contrasted with higher investments for the substations. Because of small temperature differences, the pump energy required in 5th generation district heating and cooling networks increases. Up to now, there are only few measurements that investigate this relationship. In the presented networks, values between 1.6 % and 3.2 % of the delivered heat could be observed. The higher operating costs for the electricity of the heat pumps are also given as a possible disadvantage. As additional challenges, the authors state the need for new planning tools for these systems and the integration of existing buildings with high supply temperatures. As with all heating networks, 5th generation district heating and cooling networks require ground works to install the infrastructure and the decision to connect to the network often lies with the end customer.

We think the very good overview of already installed systems in Europe is particularly interesting. In Switzerland and Germany (15 networks each), many of these systems have been installed in recent years and are now in operation. About 70 % of the networks have an installed heat capacity of 3 MW or less, the largest system has a capacity of 10 MW. The low installed capacity compared to conventional district heating networks indicates that these systems are mainly used in smaller districts so far. The authors indicate a line density of 1.2 kW/m for the economic operation of a district heating network. In 16 of the 40 systems, the line density was analyzed in more detail. Nine of these 16 systems have a line density lower than 1.2 kW/m, which is particularly interesting for new buildings with a low heat demand.

Most of these 5th generation heat networks use shallow geothermal energy as a heat source. Other ambient heat sources are lake, river or sea water. In seven of the networks studied, low-temperature waste heat is used, which is considered to have particularly promising potential for the future. The network temperatures vary between -5 °C and 35 °C. In the investigated networks, values for the SCOP (seasonal coefficient of performance) between 2.5 and 6 (mean > 4) for heating and 7 - 12 for cooling (seasonal energy efficient ratio - SEER) are observed. In all networks investigated, electric heat pumps were used in the substations, which were operated either with a simple on/off control or with modulation. If there is a demand for domestic hot water in the building, a buffer storage tank is usually installed. For cooling, a heat exchanger to the thermal network for free cooling is used in several networks investigated.

This paper introduces the topic of 5th generation district heating and cooling networks. Of course, not all aspects of these energy systems can be covered in full detail, but the paper presents the advantages and disadvantages, as well as the opportunities and risks of the 5th generation heating and cooling networks in an unbiased way. Especially the statement that the networks are based on similar mechanisms, but due to the individual use of the local heat sources, each network is very individual, is well in line with the experiences from past and current projects at heatbeat. Especially within the research project TransUrban.NRW we currently apply our models to support the planning and commissioning of 5th generation district heating and cooling networks at 4 sites in North Rhine-Westphalia. The flexible and object-oriented structure of our simulation models in Modelica enables us to develop customized solutions and thus dynamically model the system states already in the planning phase.

Further information

The original article can be found at https://doi.org/10.1016/j.rser.2018.12.059. Further research from the same authors include the already completed EU-funded research project FLEXYNETS (http://www.flexynets.eu/en/) as well as the currently ongoing projects Life4HeatRecovery ((http://www.life4heatrecovery.eu/en/) and REWARDHeat (https://www.rewardheat.eu/en/) which all investigate interesting aspects of modern district heating networks with contributions to make the systems more flexible and efficient.

Feedback on the third issue

At the end of this third edition, we would like to invite you again to give us feedback so that the newsletter can offer you the greatest possible value. Do you have any ideas on how we can make the newsletter more valuable to you? Then contact us at newsletter@heatbeat.de