Saves energy and cuts carbon emissions

The Danish Board of District Heating (DBDH) in a story that appeared in the October issue of its newsletter, has reported that despite its extremely mild summers, Copenhagen, needs air conditioning in office buildings with large server rooms or work places and shopping centres accommodating a large number of people. In the light of this, it has efficiently tapped its seawater for district cooling.

Gerdes reported that two years ago, Copenhagen Energy (Københavns Energi) opened the city’s first district cooling plant, a 10-megawatt (MW) facility located on the site of an obsolete power plant on Adelgade, to complement the city’s existing district heating system, which is reportedly the world’s largest, covering 98% of Copenhagen.

Gerdes, who was on a reporting trip to Denmark, was given a guided tour of the plant by Thomas Grinde, an engineer with Copenhagen Energy, who explained how the system works: When the temperature of the water in Copenhagen Harbour is sufficiently cold, the district cooling system draws water from an intake pipe located near the Royal Danish Playhouse and Nyhavn Canal. Care is taken to separate small marine life at the intake and introduce into a suitable habitat. Every degree saved by pre-cooling with seawater, reportedly saves 15% on electricity at the chiller.

View of Copenhagen district cooling facility (Photo: Justin Gerdes)

The following are claimed to be the advantages of diverting seawater for DC:

• All cooling demands are covered by free cooling heat exchangers.
• Heat exchangers are used for pre-cooling of the cooled water, before it is fully cooled by chillers to the desired temperature.
• The seawater is too warm to be used for free cooling. So, absorption and compression chillers provide all the cooling. Free cooling exchanges are bypassed completely.
• Insulated pipes which carry chilled water to commercial and industrial buildings for indoor cooling can be located in the same underground tunnels that carry steam for the district heating system or in entirely new networks – the endeavour is to target co-located buildings like department stores, commercial buildings, hotels, and data centre facilities with cooling demands of 150 kilowatts (kW) or more.
• The integration of the already efficient district heating and cooling systems into one network leads to incremental efficiency – in summer, when heating demand falls, surplus heat from Copenhagen’s combined heat and power (CHP) plants is re-directed to the steam-powered district cooling chillers.
• Sending steam to the district cooling plant helps maintain a balance between the two systems and compensates for the lack of free seawater cooling.
• Adopting district cooling in hotels can create more parking space in the basement where the compressor would typically be placed, as also freeing up rooftop space that would be occupied by cooling towers.
• It is aimed at customers with large cooling needs who pay a fee to connect to the network and subscribe to the service based on their expected and actual load. (The system does not offer the service to residential customers.) The upfront fees help pay for the build-out of the system.

With rising summer temperatures, Gerdes said, Copenhagen expects cooling demand to increase in the coming decades and the need for as many as seven district cooling zones.