Therefore, Taarnby Forsyning and the consumers could not agree on how to harvest the benefits of the traditional combined district heating and cooling (DHC). Fortunately, we found the key to increasing profitability by including more sector couplings based on favorable local conditions. Therefore, Taarnby Forsyning could give an even better offer to the first two consumers, Ferring and Skanska, which they could not resist. The consumers paid a connection fee, which was competitive compared to the alternative building level chiller. This co-financing was sufficient to attract additional commercial financing and establish DC as a new business unit of Taarnby Forsyning. Besides, the consumers pay a fixed annual fee per kW and a variable seasonal energy fee per MWh, which is competitive compared to traditional chillers.
The heat pump was put into operation in spring 2020, and the first cooling consumers are connected in spring 2021. The project has been implemented according to the plan and budget, within a minor deviation.
In the following, we describe the features and sector couplings, which improved the cost-effectiveness of the district cooling:
Energy planning - the key to profitability
The municipal owned multi-utility
In the first screening of the DC potential, we could see that DC in the district, due to economy of scale and sector integration, could be very profitable for the society of Denmark, and the local community in Taarnby, including Taarnby Forsyning and the cooling consumers, compared to cooling at the building level. Traditional DC benefitting from the economy scale and combined heating and cooling would be cost-effective. However, that was not enough to overcome the various barriers due to the large initial investments and the legal obstacles. A heat pump at the wastewater treatment plant extracting heat from the wastewater (and thereby wasting valuable cooling capacity and cold energy into the wastewater) would not be cost-effective due to the efficient heat from the Greater Copenhagen DH system. However, by combining these two projects for heating, cooling, and wastewater, the project was very profitable, and it was possible to overcome the barriers.
As the municipality owns Taarnby Forsyning, the company's overall aim is to be efficient and create value for money for the residents and businesses in the municipality. As a multi-utility, it can explore synergies between the city and the municipal services, in this case, heating, cooling, wastewater, and water. We could benefit from three essential couplings: • The wastewater treatment plant was upgraded with facilities to clean the air from the process and thereby paving the way for the new business district next to the plant and thereby also consumers to the district cooling • Themanagement of Taarnby Forsyning could decide that the best solution would be to allocate available space at the wastewater plant for the energy plant and the storage tank, as land in the business district was limited and very expensive. • The max load hours of the heat pump could be increased from 2,000 to 6,000 hours by using the available cooling capacity to extract heat from the treated wastewater. This double use of the heat pump was the most crucial key to the project. And not to forget, it was important that the staff of Taarnby Forsyning had a vision and refused to give up and that all three utilities were under one umbrella.
The heat pumps
The energy plant is the heart of the system. It is connected to the cold water storage tank, to the district heating and cooling grids, to the wastewater outlet, to the 10 kV power grid via a transformer owned by Taarnby Forsyning, and it will be connected to ground source cooling in the second stage. The heat pump installation includes four ammonia heat pumps in two parallel lines in two steps. The total capacity 6,5 MW heat and 4,5 MW cold. The supply temperatures are 8 °C to the district cooling and 75 °C to the district heating.
The buildings
Combined DHC offers the building owners additional benefits, saving valuable space for technical installations in the basement and on rooftops and eliminating the local negative environmental impact of advanced facilities in the buildings.
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