Improved hydronic balancing of the district heating network in Slovenia

Thursday, February 3, 2022




The Saleska Valley district heating network is the second largest network in Slovenia, covering two major cities and industrial estates through 400 km of distribution pipelines. The network dates back to 1959, and since then demands have changed significantly. These changes challenge the hydronic balancing of the system.

The system has to cope with great variations in the operating conditions. The winter in Slovenia is cold and the heating demand is high, whereas the summer is hot with no need for heating, only domestic hot water supplies. The network also supplies several large industrial estates with fluctuating demands; and besides, the district heating system has been prone to major outages, leaving consumers with no heating or hot water for hours.

As is the case in many, older systems, the poor hydronic balancing results in inefficient heat utilization on the secondary side, while oversized control equipment tend to increase the return temperature. The low temperature difference leads to increased pumping cost, substantial heat losses and increased energy consumption. This again leads to excessive CO2 emissions, high operational costs and poor user satisfaction.

“We were facing serious challenges and sought a solution that would improve the hydronic balance of the system and thereby ensure steady and sufficient supplies to the two main pipelines that supply the valley’s major cities of Velenje and Sostanj.” Rok Miklavzina, Senior Distribution Engineer.

Komunalno podjetje Velenje - station

Poor hydronic balancing solved with new pressure and flow controllers

The district heating utility and Danfoss worked closely together to map the system performance over a period of timein order to identify the main challenges in the network. It soon became evident that the major problems were related to the biggest consumer in the network, Company Gorenje, which experienced fast pressure changes and to the Sostanj network branch that experienced extremely high pressure variations and insufficient supplies.

In order to solve the problems at Gorenje, the district heating utility decided to install a self-acting differential pressure regulator to minimize differential pressure variations and improve control stability throughout the network right down to the individual consumer. At the Šoštanj network branch, the utility installed a two-stage pilot regulator to stabilize differential pressure to obtain stable operation even at high pressures and to stabilize distribution between the two branches.

The regulators were selected from the Danfoss Virtus portfolio of intelligent pressure and flow controllers that allow precise and stable control of the differential pressure at all times. Furthermore, the utility decided to add the iNET solution that enables real-time, remote control of the regulators to secure high efficiency no matter the operating conditions.

“We can clearly see how the combination of the Virtus regulators and the iNET remote control increases the efficiency of the system.” Rok Miklavzina, Senior Distribution Engineer.

The Virtus intelligent pressure and flow controllers are especially designed for district energy purposes, and offer big flow capacities and optimization of the network operation and performance. When adding iNET, the solution provides real-time alignment of heat production and distribution to the actual consumption.

Overlooking the thermal plant Sostanj

The new solution has been running for a couple of years, and the results show a great improvement of the hydronic balancing throughout the network.

“Experience with the use of the Danfoss solution during the past year certainly shows that the installed equipment maintains the network’s differential pressure within the desired or set limits, which is essential for us.” Rok Miklavzina, Senior Distribution Engineer.

The tangible benefits of the Virtus + iNET solution in the Saleska Valley are:

  • Improved efficiency, reduced energy consumption and climate impact
  • Short pay-back time, estimated to be 1-2 years
  • Stable operation with fewer network failures and faster recovery of the system in case of failures
  • Less stress on pipelines, pumps and other equipment
  • Improved user comfort and satisfaction
Rok Miklavzina at the heating station, Velenje

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