Smashing the silos

At Ramboll, we see the energy system as consisting of four energy carriers: the electrical system, the gas network, the district heating network and the district cooling network.

Traditionally, the four energy carriers are considered separate and have not been thought together. However, connecting the various elements and utilising the strengths of each of the four energy carriers can establish the required flexibility of an energy system where the share of green energy is increasing.

Sector coupling

Therefore, in the energy system of the future, it is important to smash the silos between the four energy carriers and demonstrate how smart sector coupling can provide the states and the local communities with more clean and low-priced energy services.

How smart sector coupling helps Taarnby produce low-carbon energy

Smart sector coupling between heating, cooling, and electricity is one of the most accessible solutions for decarbonising the energy system.

A great example of using smart sector coupling is the new urban development district at the Kastrup Metro station in Taarnby Municipality, a suburb in Greater Copenhagen and the first to combine district heating with district cooling and wastewater to produce low-carbon energy for the growing community and business sector in the area.

Taarnby diagram

The public multi-utility in Taarnby, Taarnby Forsyning, has established a new district cooling system and an extension of the existing district heating system to replace existing gas boilers. The new district cooling system consists of an energy plant and a 2000 m3 chilled water storage tank. The energy plant, located in the outskirts of the wastewater treatment plant, has four heat pumps that can generate combined heating and cooling and use the surplus cooling capacity to extract additional heat from the treated wastewater.

The wastewater treatment plant with roof covered basins is a smart way of preventing bad smell, allowing the new urban development to be placed so close to the facility. Moreover, the buildings supplied with district cooling will have more space available and avoid the noisy chillers on the rooftop.

The wastewater 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 both district cooling and district heating. However, treated wastewater 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.

According to the Ramboll’s business plan, an existing drain water resource or an ATES plant utilising ground water will be set up to meet the increased demand for cooling in the area. The heated ground water will supplement the heat from the wastewater during winter and generate cooling in summer. Thereby, the efficient heat from combined production of heat and cold is increased during the winter months and reduced during the summer months considering that the production cost of heat to the heat transmission system from the waste and the biomass CHP plant is lower in the summer.

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. During periods when the price of electricity is lower, typically at night, the heat pumps can store cold water for the end-users during the day. Even more important, the heat pumps can down-regulate in case of large electricity prices and in case of capacity problems in the power grid.

When operating, the heat pumps generate 4.5 MW of cooling and 6.2 MW of heating. 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 to end-users from the heat pumps, ground water and storage tank is 10 MW.

The return of investment for the local community is equal to 45% compared to alternative large investments in chillers at the buildings. This corresponds to an economic net present value benefit of DKK 80 million.

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