HOT|COOL NO.2/2021 - "Economics, Finance & Money"

The Kastrup Business District and public transport

The Wastewater treatment plant

Taarnby Forsyning has, since the suburb of Taarnby was established more than 100 years ago south of Copenhagen, been responsible for water and wastewater in the municipality and wastewater treatment. Today, the wastewater treatment plant processes wastewater from 43,000 inhabitants and Copenhagen Airport. It has become a vital asset of the municipality hosting the DC facilities and being a source for heating and cooling.

The new metro to Copenhagen Airport in the year 2000 was the starting point for a new business district between the Kastrup Metro Station and the sea. The old industrial district was upgraded, not least as the bad smell from the wastewater treatment plant was eliminated and paving the way for the new urban development. The first new building close to the plant, the Blue Planet aquarium, was inaugurated in 2010. The remaining 170,000 m2 of offices and hotels will be established from 2021 to 2025. Efficient public transport attracts offices and institutions, which all have a cooling demand, and we can conclude that the metro and DC goes hand in hand in the Danish climate. In fact, having established the DC branch and filled up the tank with cold water, it took only two months to negotiate contracts with three more consumers in the second stage.

The District Heating network

The DH system was established as a new branch of Taarnby Forsyning in 1980, as Taarnby Municipality joined the Greater Copenhagen district heating system. Today the system distributes almost 100% renewable heat from CHP plants fueled by waste and biomass, in total 180,000 MWh. A project for extending the network with an additional 50,000 MWh is in the pipeline. That is enough to ensure all heat from the heat pump to be utilized even on warm days. The heat pump will generate 20-25% of the total production to the network. Taarnby Municipality has, following the Heat Supply Act, approved that Taarnby Forsyning can supply DH to all buildings in the district replacing gas boilers, as DH is the most cost-effective heat supply form in the Kastrup Business district. The network can be operated at temperatures up to 95 °C, but fortunately, the consumers around the heat pump can accept 75 °C, which a two-stage heat pump can provide.

The chilled water tank

A 2.000 m3 chilled water pressureless steel tank was established next to the heat pump installation. The cold storage capacity is around 13 MWh, delivering 2 MW cold in 6 hours, or 8 MW in 1.5 hours. The tank's purpose is to deliver this peak and spare capacity and allow the heat pump to be operated cost-effectively and concerning the fluctuating electricity prices and the value of heat in the Greater Copenhagen DH system.

The district cooling network

As Taarnby Forsyning operates both PEH pipes for water supply and pre-insulated steel pipes for DH, there has been a fair competition between the two pipe concepts. The main reasons for choosing the pre- insulated pipe technology have been that it would be possible to detect leaks and guarantee the same water quality as in the DH system. The additional investments in the pre-insulated pipe network were modest due to the short distance between the consumers.

The ground source cooling

To provide additional cooling capacity in summer and to store cold from winter to summer and heat from summer to winter, the plan is to install ground source cooling in the second stage. Thereby it will be possible to use the maximal heat capacity of the heat pump in winter, even if the process cooling demand will be less than expected and the wastewater flow will be lower than average.

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