Customer application September 18, 2020

Efficiency in District Heating Control Center

In Flensburg, they make their own electricity – and, for more than 30 years, have done so in connection with a district heating network. When it commissioned a new gas and steam turbine system in the fall of 2016, this city on the Baltic Sea bid adieu to coal; it now uses natural gas for the district power-heat coupling. In parallel, this city in Schleswig-Holstein also modernized its district heating network. Control technology from WAGO is used for the decentralized control, as well as the connection to the remote monitoring.

The municipal utility supplies the primary circuit of the district heating network with at a supply temperature of 110 °C of – it is able to tap into the thermal energy produced by the power-heat coupling in the city’s power plant for heating and hot water. There is broad acceptance of district heating in Flensburg and the surrounding areas. Frank Nicolaisen, Team Leader in telecontrol transmission technology at the municipal utility, cites as proof the impressive connection participation rate of 98 %. “District heating is politically popular and is thus easy to support in Flensburg.” The municipal utility currently supplies 60,000 customers in Flensburg, Harrislee, Glücksburg, Tastrup, Wees and the Danish border city of Padborg.

The Benefits of WAGO for You:

Decentralized control and connection to the remote monitoring
TCP/IP communication per IEC 60870-5-104
Efficient need-based control

Using High Temperatures in the Primary Circuit

To achieve this, water heated by the power plant past the boiling point is initially pumped into a primary circuit that extends several hundred kilometers and remains there in a fluid aggregate state at a pressure of up to ten bar. Thanks to this combination, the water can be conveyed through the conduits at a high energy density, which makes transport through the longer stretches more efficient. In order avoid safety issues at the customer end as a result of this effect, houses, apartments and commercial properties are supplied by intermediate heat transfer stations. There are just under 100 of these distributed throughout the supply area – and they are currently being modernized with automation technology from WAGO. In the equipment rooms, which appear unimpressive from the outside, the primary circuit delivers its thermal energy to a second network via plate heat exchangers. The heat exchangers reach maximum supply temperatures of 95 °C and thus remain safely below the boiling point. Only then does the hot water flow into heat exchangers in the residential and commercial units.

Previously, the control center of the power plant, located in Flensburg’s harbor area, had no data access to the pumps and valves in these stations. If there was a fault, or a valve shut off due to temperature overages in a water circuit, the shift workers had to be satisfied with an error list signal. This was transmitted from the transfer station to the control center via a telephone connection. “However, we didn’t know exactly what it concerned,” explains Frank Nicolaisen, “which meant that a technician had to go trace the problem on site.” According to the experiences of the two technicians Horst Jordt and Vitali Kerner, these were exactly the situations that regularly wasted time and made their work less efficient. Then, the heat regulators, which had been used for years, were discontinued, which lent urgency to the planned modernization.

One System That Does It All

During the tendering phase, they were convinced by WAGO above all “because the system can do everything that we need,” according to Frank Nicolaisen. The requirements profile initially included TCP/IP communication per the IEC 60870-5-104 telecontrol protocol standard. The municipal utility also pursued the goal of connecting complete sensors and actuators in the simplest way possible. One example is found in the directly switched Pt100 temperature sensors. “Even if some of the well-known manufacturers were also able to use the 104 protocol, we would still have needed a signal conditioning module for our thermometers,” explains Horst Jordt. “WAGO was the company that could do everything, and they significantly simplified the entire installation for us.”

In a transfer station that has already been modernized, the starter motor for the circulation pump is directly controlled by the controller (750-880/025-001); therefore, the municipal utility was able to do without a complex frequency converter for speed control. Such functions are now programmed in the standardized languages of IEC 61131-3. For telecontrol technology, WAGO offers a specifically-matched telecontrol configurator for its controllers, in which standard functions are mostly pre-prepared and thus only need to be configured.

Direct Access Increases Efficiency

By using this equipment within the district heat supply network, the Flensburg municipal utility increases the efficiency of its personnel, because employees can log into the technology on site using remote maintenance access. For Frank Nicolaisen, the TCP/IP communication with WAGO’s 750-880 Controller as the head station functions as the foundation for running the entire district heating supply on an as-needed basis; this lets him configure the energy flows more efficiently.

In another project – in which Flensburg is truly striking out into uncharted territory – the municipal utility wants to supply a new residential area with the return flow, instead of the forward flow. “A water temperature of about 50 °C is still sufficient for heating. To prevent problems with Legionella bacteria, this is planned in combination with small instantaneous water heaters,” says the Team Leader, revealing the plan for the district heating technology. If everything functions as planned, then Flensburg can achieve a further efficient increase. The technical prerequisites are already met, due to the modernization of the transfer stations, and the political support is also there.

Text: Daniel Wiese, WAGO

Photo: Thorsten Sienk

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