Deep Water Cooling, Södertälje Sweden

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Deep Water Cooling, Södertälje Sweden

In addition to ordinary utility services, Telge Energi, a publicly owned utility company, offers an extra-ordinary service in Södertälje, Sweden—deep lake cooling from Lake Mälaren. And FVB helped them solve the engineering issues and get this innovative utility service into operation. What makes Lake Mälaren attractive is that the temperature at 40 to 50 meters (130-160 ft) never rises above 9oC (48oF), and thus can be used to satisfy the cooling needs of Telge Energi’s largest customer, pharmaceutical AstraZeneca, as well as the Södertälje buildings that subscribe to the district cooling service. Although the fresh water of Lake Mälaren is not corrosive, special attention had to be paid to the different forms of algae and how those forms vary depending on depth, temperature, and even season of year. The bottom line? With a production demand of 60 MWth (17,000 tons), the benefit of using this near zero-cost energy source offsets the capital expense of the 6000 m (3.7 mile), 1000 mm (39 in) distribution pipeline. Of course pumping the water requires electrical energy but still, the deep lake cooling system uses one tenth of the energy a conventional cooling system uses. And there are no refrigerants to stock-pile and no compressors to fix when they break down.

• Production capacity: 60 MWth (17,000 tons)
• Supply temperature: Less than 9oC (48oF) all year long
• Source depth: 45 m (148 ft)
• Supply flow rate: of 6000 m3/h (26,400 gpm)
• District cooling distribution: 6000 m (3.7 miles), 1000 mm (39 in) diameter polyethylene pipe
• AstraZeneca (83%)
• Commercial buildings (17%)
FVB Energy, Inc. Services
• Technical and economic assessment of alternatives, including evaluation of water temperatures, water quality, location of pump and intake and pipe materials
• System design

Storing Cold Sea Water For Summer Use
(Sollentuna, Sweden)

Sollentuna Energi receives its cooling energy from 15 m (50 ft) below a nearby Baltic Sea bay. Although the bay is cold in winter, the summertime temperature is not cold enough to use for district cooling. To overcome this shortfall, FVB recommended storing the cold from the bay in an underground aquifer during winter and then using the cold aquifer water for district cooling during summer. In close cooperation with Sollentuna Energi, FVB evaluated the technical and economic feasibility of this project, assessed the district cooling market, and provided engineering services from concept through commissioning. In our design, the brackish sea water never comes into direct contact with either the aquifer water or the district cooling water but rather is separated from them using plate and frame heat exchangers. Additionally, to protect the aquifer from contamination, the aquifer side is separated from the district cooling system using plate and frame heat exchangers. With a volume of 400 000 m3 (106 million gallons), the aquifer can store up to 2600 MWth (730,000 ton-hrs). At present, this storage capacity is adequate to meet the 4 MWth (1,100 ton) system demand all summer long.

• Production capacity: 4 MWth (1,100 tons)
• Storage capacity: 2600 MWth (730,000 ton-hrs)
• Supply temperature: 7oC (45oF)
• Source depth: 15 m (50 ft)
• Pipe material: polyethylene for pipe installed in the bay, carbon steel for underground pipe, and stainless steel for customer connections

FVB Energy, Inc. Services
• Market assessment and feasibility analysis
• Hydraulic modeling
• Final design documents, including bid tender documents for deep lake pipeline, pump stations, district cooling pipeline, and energy transfer stations
• Bid evaluation, construction observation, and commissioning
• Financial analysis and rate structure development
• Marketing and sales guidance and support
• Energy services agreements with customers