New accumulator tank provides spare capacity in Uppsala

The need for district cooling is growing sharply in Uppsala and feasibility studies for a new accumulator tank for the district cooling system started back in 2015.  An accumulator tank can be compared to a giant thermos where cold 6-degree water can be stored. The cold water is pumped out to the network during power peaks, while storage is done during power dips. This way, the number of occasions of starting and stopping costly production can be reduced. The accumulator tank is about 35 meters high and contains 20,000 cubic meters of water.

A brand-new accumulator tank for district cooling is being connected to the existing tank, while cooling production keeps going at Vattenfall in Uppsala.

Todd Sivertsson is a senior consultant at FVB and has worked as a researcher and technical advisor on the project.

“FVB has participated all the way, from idea to completion. The assignment started with evaluating the production options and then continued with request for tender for both the pump station and the accumulator tank, a functional description of the entire facility and detailed planning of pipes for the pump station. At the time of writing, we are acting as technical support during the commissioning,” says Todd.

At first, the request for tender was written as a contract for both the tank and the pump station. However, it turned out that there were no contractors who could take on the work of developing the pipe design for the pump station, so the assignment went to FVB.

Keeping the existing tank

Uppsala chose to keep the existing accumulator tank of about 3,000 cubic meters, which is placed so that the water level is about 12 m lower than in the new tank.

Todd thinks it is quite unusual to have more than one accumulator tank in a network and the difference in water level has posed quite a few challenges.

“The tanks intercommunicate, so nature wants to even out the level. This means that the existing tank overflows unless level control and protective measures are introduced. We have essentially solved this with a level control valve that only lets back in as much water as is pumped out from the existing accumulator tank.

Uninterrupted supply

Another challenge has been to perform testing and commissioning in a way that does not interrupt the customers’ supply. Production has to always be up and running, which requires thorough planning of how the different parts are shut down.

Although the project has been going on since 2015, it has been at full speed the entire time.

“It is important to stick to the schedule for the facility to be ready this summer when the need for district cooling is at its peak,” says Todd.

For more information:
Todd Sivertsson, 021-81 80 59

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