This summer, Danish renewable energy specialist Aalborg CSP secured yet another district heating related order; this time in terms of a turnkey contract for a 2,5 MW heat pump for wastewater. The order is awarded by E.ON Denmark and is to be used for heat production in Frederikssund, Denmark. By establishing the new heat pump at the local wastewater treatment plant, E.ON Denmark will be able to further optimizing their green district heating supply in Frederikssund by utilizing the energy from wastewater for more climate-friendly district heating with a high efficiency and at the same time benefitting local environmental habitat by lowering the temperature of the water in the Roskilde Fjord.


Heat pumps are becoming a preferred technology within the Danish district heating plants as well as with our German neighbors as heat pumps are now considered an important part of the continued green transition in Denmark as well as internationally. The order for E.ON Denmark consists of turnkey contract for a heat pump with associated exchanger, piping and purification system, which will be extracting the energy from the treated wastewater before it is subsequently discharged into the local environment at Roskilde Fjord.

Custom made heat pump with high COP

With the establishment of a wastewater heat pump, E.ON Denmark joins an increasing number of Danish utility companies, who have introduced and integrated heat pumps into their district heating production. The heat pump itself, which applies the natural refrigerant ammonia (to be completely renewable and nontoxic), will have a maximum output of approx. 2,500 KW. The heat pump is custom made for E.ON Frederikssund to ensure a high COP (Coefficient Of Performance). This, in order to guarantee that the consumers obtain as high an amount of kWh district heating as possible from the kWh of electricity supplied to the heat pump.

The wastewater temperature varies throughout the year and the plan for the heat pump in Frederikssund is to extract approx. 7° C from the wastewater. By means of the heat pump, the temperature is increased to approx. 70° C depending on the season in question, after which it is subsequently supplied directly through the district heating pipes in Frederikssund


Sustainable, yet complex and flexible system

It is a pure «win/win» situation to recycle the energy from wastewater and at the same time using part of the increasing green electricity from the grid. On the one hand, it is positive for the aquatic environment that the outlet temperature of the treated wastewater is decreased and is hence closer to the temperature of the aquatic environment in which it is discharged. Likewise, it is positive for district heating consumers, as the relatively high temperature of wastewater ensures a more stable and sustainable energy supply. In addition to the climate benefits that the new heat pump solution provides, the solution is furthermore designed flexibly in a manner which allows for changes in the heat source, thereby giving certainty to the bankability of the long-term investment. A possible switch of heat source can allow the plant to utilize the outdoor air as an energy source if the treatment plant were to be closed down in connection with potential future changes in the wastewater plan.

Using wastewater as an energy source is not a new technology, but at the same time it is challenging to design such plants with high reliability to ensure safe operation. Aalborg CSP has therefore prepared thorough studies of the area, in order for all known challenges to be taken into account in regard to the final installation for E.ON Frederikssund. The wastewater filters used, automatic treatment of exchangers and special exchangers and more are all of a very high quality, in order for it to be able to withstand the use of wastewater. This well-thought-out and flexible quality solution was one of the main reasons why Aalborg CSP was awarded the order.



  • Client: E.ON Denmark
  • Capacity of the heat pump: 2,5 MW
  • System supplier: Aalborg CSP A/S
  • Scope: Turnkey EPC contract including integration
  • Placement: Frederikssund, Denmark
  • Maximum temperature: 75º C
  • Type of heat pump: Ammonia heat pump with 2 stage compressor
  • Life expectancy:  25 years

Aalborg CSP A/S is a leading developer and supplier of innovative, renewable technologies with the vision Changing Energy aiming at changing the way energy is produced and stored today. We design and supply green solutions and integrated energy systems based on solar power, energy storage within power-to-X (PTXHEAT and PTXSALT), heat exchange and much more for industries and power plants worldwide.

Since 1988, Aalborg CSP has utilized its immense expertise within design and delivery of boilers, complex systems, renewable energy technologies and energy storage. Thereby, we have a deep understanding of individual energy needs, technology- and system integration as well as optimization with key competences such as performance modelling and system design.

Aalborg CSP A/S places strong focus on R&D activities and works both internally within the company and externally with Danish and international knowledge-based companies and institutions in continuously creating innovative and sustainable technologies.

Aalborg CSP offers a wide variety of renewable energy solutions including high- and low temperature energy storage, solar panels, heat pumps, boilers, integrated energy systems as well as customized Power-to-X solutions. We match individual energy needs with the right systems and technologies and integrates and combines solutions to achieve synergies between both sectors and technologies. We do so in order to create optimum value for our clients, while also optimizing the utilization of the world’s energy sources aiming for a CO2 neutral future.

Headquartered in Aalborg (Denmark) and with a sales & service office in Spain, Aalborg CSP A/S has realized cost-effective green energy solutions worldwide.

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