Smart combination of district cooling, district heating and waste water in Taarnby

3D illustration showing a positive indication of the visual impact of the district cooling plant and storage tank (green) in Taarnby

3D illustration showing a positive indication of the visual impact of the district cooling plant and storage tank (green) in Taarnby


Anders Dyrelund

Anders Dyrelund

District Heating and Energy Planning Specialist
T: +45 5161 8766

This project demonstrates how smart cities are built on smart solutions that promote synergies between energy and the environment while benefiting the local community.

Denmark is well-known for championing sustainable initiatives, being cited globally as an example to follow when addressing questions related to the future of energy. In fact, Denmark seems to have grasped the formula for a sustainable and cost-effective approach to energy without compromising on economic growth and community development.

Providing a sustainable solution for the local community in Taarnby

In 2014, Ramboll prepared a screening of the district cooling potential for a new urban development area as an ad-on to the existing heat supply planning. The developers were in the first stage only interested in district heating. 

In 2017, Ramboll prepared a feasibility study demonstrating that district cooling in combination with district heating would be a very profitable solution for the local community in Taarnby. In continuation of the feasibility study, Ramboll prepared a business plan and project proposal for approval in the city council. 

The business plan highlighted the profitability of establishing a district cooling system based on a central large-scale electric heat pump installation and a chilled water storage tank as well as the additional benefits of using a heat pump in combination with ground source cooling and waste water.

Based on this assessment, the client subsequently decided to establish a new district cooling business unit that will service the new urban development area, located north of Copenhagen Airport. Following the approval by the board and the municipality Ramboll prepared:

  • Design of all installations in the energy plant
  • Design of the network for heating and cooling including no-dig method
  • Design of connection to the waste water treatment plant
  • Design of connection to the power grid
  • Tender documents for pipes, tank, installation and building
  • Supervision of all construction work for network and energy plant

Optimised efficiency by combining district heating with district cooling 

The new district cooling unit consists of four heat pumps, a cooled water storage tank and a waste water treatment plant. The heat from the waste water can be extracted via the heat pumps resulting in two important energy resources: hot water for district heating during winter and cold water for district cooling during summer. Depending on the different demands and resource availability, the heat pumps can also produce cooling and heating at the same time.

The waste water plays a central role in the set-up and treating it locally at the plant has a special advantage. Traditionally, sea water would have been considered for district cooling. However, treated waste water represents a better solution not only in terms of pricing but also because it generates stable temperatures between eight and ten degrees all year round as opposed to sea water which is too hot during summer when the need for cooling is the greatest. 

In addition, an ATES plant utilising ground water will be established to meet the increased demand for cooling in the area. The heated ground water will supplement the heat from the waste water during winter, since the production cost of heat in the summer is low in the heat transmission system.

The unit is fully automatic, constantly checks prices and the needs of the end-users. Thus, it can always ensure maximum use of the resources. For example, during periods when the price of electricity is lower, typically at night, it would be beneficial to run the heat pumps to store cold water for the end-users during the day. 

The new cooling unit will complement the existing district heating system, which produces energy cost-effectively based on biomass fuelled cogeneration (CHP), residential waste and natural gas, covering around 60% of the total heat demand for large buildings in the municipality, including the Copenhagen Airport. 

When operating, the heat pumps will generate 4.5 MW of cooling and 6.2 MW of heating energy from the waste water. The ATES plant utilising ground water is expected to generate an additional 2.8 MW of cooling. On a hot day, the total cooling capacity that can be delivered from the heat pumps, ground water and storage tank is 10 MW.

All numbers are favourable 

The project will deliver low-carbon heating and cooling in a cost-effective way improving the efficiency of the energy system. Overall, it will supply cooling to businesses, in total 200,000 m2, and heat corresponding to the annual demand of 500,000 m2. The total investment of DKK 80 million is roughly equal to the alternative investment in cooling at each building. The return of investment for the local community is 45% corresponding to an economic net present value benefit of DKK 80 million.

About the client

Taarnby Forsyning (TF) is a public utility in the municipality of Taarnby in the Copenhagen area. 

The public utility has for decades been responsible for water and waste water supply in the municipality of Taarnby, a suburb south of Copenhagen including the airport. In 1981 the utility started to implement district heating in 50% of the municipality and is now co-owner of CTR, which is a partner of the Greater Copenhagen district heating system. 

Ramboll has been a trusted advisor to TF since 1980. Over the years, we have assisted TF with several energy endeavours, encompassing all sorts of energy planning and district heating projects and now district cooling too.



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