New pump optimizes district cooling in Stockholm

“To find room for the pipes for the new pumps in Stockholm Exergi’s district cooling plant in Ropsten, we literally had to think outside the box and implement an unconventional pipe solution. It was a successful solution in a compact building with tight spaces,” says Rikard Säll at FVB.

Not far from Värtahamnen in Stockholm is a district cooling plant that was built back in 1995. Since then, the loads have increased by several hundred percent, but the space in the plant is the same. The plant uses free cooling from lake water and if the temperature of the water is below 5 °C, it can be used directly in the district cooling system. If the water is warmer, heat pumps have to be used to lower the temperature. The installed cooling power is 100 MW and large pumps are required to generate that amount of cooling in the summer.

“The water flows through the pumps at a capacity comparable to sending a large car 100 meters up in the air every second, so these are very strong forces,” says Erik Skoglund, project manager at Stockholm Exergi.

“The system works optimally in the summer, during the winter only about 15 percent of the summer’s peak load is used. The low flow creates an unfavorable operating point for the pumps, and it has also led to vibrations. Therefore, we decided to supplement with ‘low load pumps’ to optimize the system, but we realized quickly that it would not be easy to find room in the plant,” Erik Skoglund continues.

Stockholm Exergi hired FVB to come up with a solution for how to find space for the smaller pump and associated pipes in the cramped space. This is something that Rikard Säll has spent a lot of time thinking about.

Free cooling from Ropsten is involved in supplying the entire city area, which also includes Södermalm and the Globen area. In total, about 500 properties or about 6 million square meters buy comfort cooling with high efficiency. Illustration from Stockholm Exergi).

“I like problem solving and we were really forced to find several unconventional solutions to avoid bulky piping in the building. For example, some of the pipes in the building are now hanging from springs to create balance,” says Rikard Säll, who continues:

“The pipes are very sturdy, which means they are very heavy when they are filled with water. Therefore, we’ve taken extensive measures to preserve the strength of the concrete caissons using steel forging and transverse beams. This is all to avoid the risk of cracks forming in the plant.

By the end of the year, everything should be ready, and the district cooling system will be optimized for both winter and summer operation.

Erik Skoglund is very pleased with FVB’s work and how the solution turned out in the end.

“There are not many consultants who are really good with district cooling. The best people are now at FVB,” concludes Erik Skoglund.

More information:
Rikard Säll, 08-5947 61 85

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