Case

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

Ramboll

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This project demonstrates how smart cities are built on smart solutions that promote synergies between district heating, district cooling, waste water, ground water and power while benefiting the local community.

Denmark is well-known for smart sustainable energy solutions in cities harvesting the synergis of sector integration. Taarnby Forsyning can in 2020 start operation of a unique energy plant, including heat pumps and a chilled water tank, combining smart use of electricity, district heating, district cooling, waste water and ground water /drain water.

The plant is located at the waste water treatment plant and supplies a new urben development which next to the new Kastrup Metro Station. This symbiosis between waste water and the new urban development has been possible because Taarnby Forsyning has established a roof and ventilation, which eliminates any bad smell.

In 2014, Ramboll prepared a screening of the district cooling potential for a new urban development area as an ad-on to the existing plan for district heating to the new buildings and the existing gas fuelled building. The developers were in the first stage only interested in district heating.

In 2017, Ramboll prepared a feasibility study and business plan demonstrating that district cooling in combination with district heating, waste water and ground source cooling, 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 board and 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 Taarnby Forsyning 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 and waste water
The new district cooling plant consists of four heat pumps and a chilled water storage tank located in the outskirts of the waste water treatment plant. The heat pumps connected to district cooling, district heating, treated waste water and (in second stage ground water).

First priority of the heat pumps is to deliver the necessary cooling capacity. Second priority is to extract heat from the treated waste water, which is connected to the plant via a 160 m “anergie network”. Thus, the heat pumps deliver two important energy resources: Co-production of heat and cold and additional hot water for district heating during winter “wasting the cold water in the waste water”. The optimization will take into account these synergies and respond on the electricity market prices hour by hour as well as the heat market prices in the Greater Copenhagen district heating system.

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 and as a source for heat. However, treated waste water represents a better solution not only in terms of pricing but also because it generates stable temperatures not less than ten degrees all year round as opposed to sea water which is colder in winter.
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 cold and 6.5 MW of heat. 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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