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The town of Hennigsdorf is shaped by mulity-family houses which were refurbished after the turnaround and large scale industry.
© euroluftbild.de/Robert Grahn
Climate-neutral district heating
Projektinfo 02/2018

Supply areas for the Hennigsdorf district heating network with the associated heating centres and the existing and planned heat coupling
© Ruppin Consult GmbH
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District heating network becomes heat hub

The Brandenburg town of Hennigsdorf wants to increase the climate-neutral share of heat in its district heating network to 80 per cent within five years. To achieve this, the municipal utility company is planning to integrate the waste heat from the local steelworks and large solar thermal collectors into the network. A multifunctional, arge-capacity heat storage system is intended to provide  the necessary flexibility. The concept is ready and the implementation has already started in 2017. Hennigsdorf is therefore acting as a real-life laboratory for ensuring the renewable future of the heating provision.

The municipal utility company, Stadtwerke Hennigsdorf, supplies 9,500 residential units, municipal facilities as well as 54 commercial and industrial companies with district heating, including major metal-producing and processing companies. Annual heat sales amount to around 117 GWh and the current thermal capacity is 82.5 MW. Renewable energy sources already provide half of the local district heating. In order to economically operate a biomass cogeneration plant and a bio-natural gas combined heat and power plant, an interconnected hydraulic network was created in 2009 and 2010 that links the originally four separate networks. The basic and medium loads on the interconnected network can thus be covered by renewable sources all year round.

The municipal utility company now wants to increase its share of climate-neutral heat generation to 80 per cent. To this end, two additional heat sources are being developed for the district heating supply: waste heat from industry, in particular from a steelworks and rolling mill located in the supply area, as well as heat from solar thermal systems, which is provided centrally via the municipal utility company‘s collector arrays and decentrally from customers. This requires fundamental restructuring and further development of not just the existing district heating network but also its regulation and operation.

This complex project, which is set to be implemented by 2020, will be accompanied by a comprehensive measurement and evaluation programme. Hennigsdorf‘s existing, historically evolved network is typical of a medium- sized German town and can therefore serve as a model for further developing similar networks with the aim of achieving climate-neutral district heating provision.

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Initial situation for consumers

The lower the supply temperature, the easier it is to integrate renewable energies into district heating networks. In the Hennigsdorf network, the temperatures are determined by the size of the district heating system and the customer structure, which mainly comprises apartment buildings renovated following the reunification of Germany as well as large-scale industry. In summerthe supply temperature is 85 °C and the return temperature is 60 °C. In winter, the supply temperature slides up to 108 °C. These temperatures are typical for many German district heating networks and are significantly higher than in solar thermal-based local heating systems, for example in Denmark and in German new-build pilot projects.

As part of the research work, project developers from Ruppin Consult investigated the possibility of reducing the supply temperature and the circulation rate. For this they considered both the heat transfer stations and the downstream consumption systems of numerous customers from different consumer segments. The outcome: Many heating systems are oversized with corresponding potential for optimisation. However, it still needs to be verified during practical operation whether it is at all possible to reduce the supply temperature in winter to an identified maximum of 95 °C.

Multifunctional large-capacity heat storage system

The waste heat generated by the steelworks is only produced intermittently. At the same time it must be possible to feed decentrally produced heat into the network at all times, irrespective of whether it comes from small CHP plants or solar thermal systems. In order to integrate these heat sources efficiently they need to be decoupled from one another and from the current heat consumption. For this purpose, a multifunctional heat storage system is planned which combines the capabilities provided by daily, monthly and long-term heat storage: it can absorb heat that is not currently needed, store it seasonally and, at the same time, temporarily compensate for power peaks in the network.

A large-capacity heat storage system is providing improvements for the existing biomass and bio-natural gas CHP plants. Because both have previously been heat-led, the electricity generation depends on the heat demand from the customers. If this correlation no longer applies, the overall production of renewable heat and electricity can be increased and electricity can be produced as needed.

Dynamic simulation calculations of the district heating network and the heat sources to be integrated over the long term helped in designing the storage system. With a water volume of 22,000 m³, it is conceived as a pressureless storage system with a maximum temperature of 98 °C. Since the groundwater in Hennigsdorf is very high, the storage tank will be realised as an above-ground structure made from pre-stressed and precast reinforced concrete elements. The concept is based on the design of the tank-based heat storage system used in the completed pilot project for locally utilising solar thermal heat at Ackermannbogen in Munich. Significant cost reductions could be achieved by using a „floating roof“. For this purpose, the roof structure of the Danish pilot storage tank needs to be further developed in order to permanently achieve a permissible maximum temperature for the roof structure of 98 °C instead of the currently possible temperature of just 80 °C.

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Addresses

Project management
Stadtwerke Hennigsdorf GmbH

Project coordination
Ruppin Consult GmbH

Heating network calculations
tetra ingenieure GmbH

Simulation and scientific support
Solites

Links

Erneuerbare Wärme optimal in Fernwärmenetze einspeisen
Project presentation by research initiative ENERGIEWENDEBAUEN

Effizienter Betrieb von Fernheizkraftwerken und Wärmenetzen
Project presentation by research initiative ENERGIEWENDEBAUEN

Fernwärmenetz als Wärmedrehscheibe
Short explanation movie by municipal utilities Hennigsdorf (Youtube)

ENERGIEWENDEBAUEN
Projects, reports, news and analysis from the research initiative ENERGIEWENDEBAUEN

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