SMART COST-EFFECTIVE DISTRICT COOLING IN TAARNBY

Taarnby Forsyning, the public utility in Taarnby Municipality, a suburb of Copenhagen, DK, has, despite many obstacles, established a remarkable district heating and cooling system in the new Kastrup Business District, north of Copenhagen Airport. By integrating all sectors of the urban infrastructure in the city district – in this case, public transport, district heating (DH), district cooling (DC), electricity, wastewater, groundwater, and not least, buildings – it has been possible to develop a smart and sustainable business district and offer all buildings in the business district sustainable, cost-effective and environmentally friendly heating and cooling.

By Hasmik Margaryan, Taarnby Forsyning,  Anders Dyrelund, Ramboll, Anders Carøe, Ramboll, and  Antoni Trumulis, Ramboll

Published in Hot Cool, edition no. 2/2021 | ISSN 0904 9681 |

The DH is part of the efficient Greater Copenhagen District Heating System – and Taarnby Municipality is co-owner of the heat transmission company CTR. Cost-effective, low-carbon heat from waste and biomass-fueled combined heat and power plants (CHP) is transmitted to the DH distribution networks.

Taarnby Forsyning has since 1985 distributed heat from CTR to most of the municipality to benefit the heat consumers in Taarnby. They will now distribute heat to all buildings in the Kastrup Business District.

The first screening of the DC potential in the business district indicated that all the commercial buildings would have a significant demand for cooling capacity and that DC would be cost-effective and efficient. That is entirely according to the EU directives for EE, RES, and Buildings and the objectives of the Danish Heat Supply Act. However, it was almost impossible to get started due to legal barriers and regulations.

Although it is profitable for society and the DH consumers to establish DC to new consumers and produce the cooling in combination with DH, there were several barriers in the Heat Supply Act, which was supposed to protect the heat consumers.

Moreover, the building code discriminates DH and DC compared to less cost-effective building-level solutions by defining normative energy factors, which do not reflect cost-effectiveness or sustainability and contradict EU directives.

Therefore, Taarnby Forsyning and the consumers could not agree on harvesting 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 the spring of 2020, and the first cooling consumers will be connected in the spring of 2021. The project has been implemented according to the plan and budget, with 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

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 benefits 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 significant initial investments and the legal obstacles. A heat pump at the wastewater treatment plant extracting heat from the wastewater (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, combining these two projects for heating, cooling, and wastewater made the project very profitable, and it was possible to overcome the barriers.

The municipally owned multi-utility

As the municipality owns Taarnby Forsyning, the company aims 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, such as 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, thereby paving the way for the new business district next to the plant and thereby also consumers to the district cooling
• The management 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 maximum 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 Kastrup Business District and public transport

The new metro to Copenhagen Airport in 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 wastewater treatment plant’s lousy smell was eliminated, 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 go hand in hand in the Danish climate. Establishing the DC branch and filling the tank with cold water 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, producing 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 is 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 district cooling network

As Taarnby Forsyning operates both PEH pipes for water supply and pre-insulated pipes for DH, there has been 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 heat pumps

The energy plant is the heart of the system. It is connected to the cold water storage tank, the district heating and cooling grids, the wastewater outlet, and 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 of wastewater in two steps—the total capacity 6,5 MW heat and 4,5 MW cold. The supply temperatures are eight °C for district cooling and 75 °C for district heating.

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, concerning the fluctuating electricity prices and heat value in the Greater Copenhagen DH system.

The Wastewater treatment plant

Since the suburb of Taarnby was established more than 100 years ago south of Copenhagen, Taarnby Forsyning has 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 city, hosting the DC facilities and being a source for heating and cooling.

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 cooling demand of the process is less than expected and the wastewater flow is lower than average.

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.

The secrets of district cooling

In the first stage of the project, it was impossible to find the real benefits of DC, as there were only two consumers in the first critical stage – and for safety reasons, they did not want the heat pump capacity to be lower than individual calculated.

In the long run, having up to 10 consumers, we expect to demonstrate that the total simultaneous cooling capacity is much less than the sum of all capacities installed individually in the buildings. We will monitor the actual consumption hour-by-hour for all consumers. We will demonstrate the total system efficiency, including heat pumps, storage tanks, wastewater, ground source cooling, and interconnection with the Greater Copenhagen district heating system.

We usually establish a generic district cooling system for existing buildings in 4 steps. Still, Taarnby had mainly new buildings and the opportunity to do it in only two steps.

A jolly good case-story

The project is a good case, demonstrating the benefit of local democratic ownership of utilities. This has been an essential factor in the success of the project. Still, it will also be necessary for the dissemination of experience, as Taarnby Forsyning has a common interest in sharing experiences, to mention a few:

• The approved plan was presented in Hot Cool 2/2019 and at the platform Stateofgreen shortly after the approval
• 2020 The European Heat Pump Association awarded Taarnby Forsyning in the category of sizeable industrial heat pumps
• The case of Taarnby Forsyning has been selected as the first of eight cases by the EU JRC in the study: Integrating renewable and waste heat and cold sources into district heating and cooling systems, February 2021
• The Taarnby projects for DHC are among the IEA Annex73 Towards Net Zero Energy Public Communities case studies for 2021.

Many delegations have already visited Taarnby Forsyning, and more are welcome.

For more information:
Hasmik Margaryan, ham@taarnbyforsyning.dk
Anders Dyrelund, ad@ramboll.om