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Seawater keeps Copenhagen buildings cool

Seawater keeps Copenhagen buildings cool

District cooling of buildings using seawater or surplus heat, can prevent us from emitting large amounts of greenhouse gases into the atmosphere. The very first district cooling plant in Denmark is now ready to pump cold water into distribution pipes.

At the prospect of longer and warmer summers, the need for cooling in buildings where people live, work, etc. will be greater in future. This includes buildings such as shopping centres, hotels, banks and offices, hospitals and nursing homes.

Today, many buildings of this kind have their own cooling systems. A majority of these systems run on CFC gases which, like CO2, contribute to global warming. Furthermore, they use large amounts of electricity and water, especially the more inefficient systems. They are also noisy and take up a lot and often rather expensive space. These are obvious problems which may be solved by connecting to a district cooling distribution system.

Legislation enables district cooling
Adoption by Folketinget (the Danish Parliament) of the District Cooling Act in 2008, enabled Danish municipalities that fully or partly own district heating companies to establish and run district cooling systems.  Copenhagen Energy, owned by the City of Copenhagen, had been looking forward to this opportunity for several years and was quick to take it. Today, the company has established the first district cooling plant in Denmark, in the buildings of a former power station in the heart of Copenhagen.

The new cooling station will have a capacity of approximately 15MW and is based on three different principles of cooling. This makes it a very flexible and highly energy-efficient system. The district cooling plant utilises seawater from the Port of Copenhagen in periods where the seawater is sufficiently cold, as well as surplus heat from power plants to produce environmentally-friendly cooling. Finally, the plant also uses compressors running on electricity.

The photo shows the absorber which will be converting surplus heat from power plants into cooling production. The photo was taken just hours before the absorber was craned into the cooling station in September 2009. The absorber weighs about 40 tonnes and has an output of 3.4MW.

"The technology isn't really new. We are actually only taking a known technology and applying it in a new and larger context. Of course it requires a great deal of know-how to establish the distribution system itself, but the municipalities in charge of the distribution system already have the knowledge it takes to launch similar projects," says Jan Don Høgh, head of the project at Copenhagen Energy.

Cooling customers have already been landed
Before engaging in a district cooling project, there are certain things to consider in project planning.

"Firstly, it's important to have a carefully thought through system architecture, which includes finding a suitable site for the plant, offering access to resources that would otherwise have been wasted. Resources such as seawater and surplus heating," says Jan Don Høgh.

"At the same time, the project must be feasible. District cooling is market-driven and voluntary. An adequate supply of customers in the vicinity of the plant, who can see good reasons for connecting to the system, is also important, so that the plant's total cooling capacity can be exploited," says Jan Don Høgh. According to Mr Høgh, a nine-digit investment has been made in the district cooling plant in central Copenhagen.

Mr Høgh is therefore pleased that many of the large local enterprises on Kongens Nytorv who showed prior interest in the project, have now decided to connect to the district cooling system. These include the two Danish banks Danske Bank and Sydbank, the Magasin department store, and the media group, Egmont. District cooling is primarily offered to customers with existing cooling systems of more than 150kW.

Significant benefits for climate and the environment
District cooling works on the same principles as district heating. The chilled water is produced centrally and carried to the end customers through a system of pipes.

The seawater wells are connected to the seawater by two 800mm pipes. The total capacity is approx. 2,500m3 an hour. The seawater is used for free cooling and condenser systems.

The temperature supplied from the cooling station will be around 6°C, and the return temperature is expected to be 12-16°C.

The benefits for climate and the environment are huge: According to calculations by Copenhagen Energy, comparing district-cooling with energy consumption and emissions figures for individual cooling plants in the buildings on Kongens Nytorv, there is no less than a 66% saving to be made in CO2 emissions annually. For SO2 and NOx, the saving is 62% and 69% annually, respectively. Emissions of CFC gasses can be reduced considerably as well. Emissions of 1kg of CFC gasses correspond to around 1,400kg of CO2. As a rule of thumb, there will be an average 10% CFC leak, which in the Kongens Nytorv scenario would mean CFC emissions of 100kg annually, corresponding to 140 tonnes of CO2.

More plants on the way
The district cooling plant to supply cooling for customers around the Kongens Nytorv sqaure is the first of its kind in Copenhagen. But more plants are underway. Copenhagen Energy has identified no less than eight obvious district cooling areas in downtown Copenhagen, and expects to develop the next project in the area around the City Hall Square.