Heat from groundwater in Høje-Taastrup Municipality

The local district heating company, Høje Taastrup Fjernvarme, pumps up groundwater, sends it, and the energy it contains, onwards through a heat pump and into the district heating pipelines; thus killing two birds with one stone. An excellent business case is what originally prompted Høje Taastrup Fjernvarme to start using groundwater for heat production. However, the process also lowers the high groundwater levels in the area. Previously, residents in the area experienced frequent flooding of their basements because the water table has risen by several meters over the past years. The cooled water is pumped into the Mølleåen river, which will significantly improve the living conditions for flora and fauna. Dispensation from the Danish Energy Agency was required, because the area is otherwise designated for heat supply from CHP.

• Up and running since January 2019

  The idea for the project came in 2016. Today, the facility is up and running, following only a few initial hiccups. Høje Taastrup Fjernvarme has planned for the possibility to deploy more heat pumps. They will be installed in the same building as the existing one, if the existing one continues to deliver positive results.

   

  The idea to use groundwater as an energy source for district heating production in Høje Taastrup came about in 2016.

  
  This is the first project in Denmark involving extracting groundwater for district heating production and then subsequently discharging it to the aquatic environment.

  
  Høje Taastrup Fjernvarme financed the facility and obtained dispensation from the Danish Energy Agency to build it.

  
  The facility was used as a demonstration project in the context of the - now completed - Danish-Swedish collaboration Smart Cities Accelerator, aimed at promoting local-government sustainable energy solutions.

  
  The facility has an expected lifetime of 20 years.

   

• High groundwater levels and cheap energy

  One of the focus areas in the 2030 Climate Plan of Høje-Taastrup Municipality is to safeguard the municipality's residents against high groundwater levels.

  
  Høje Taastrup Fjernvarme has an ambition to provide locally sourced, cheap heating.

  
  The municipality has an interest in the project because of the greater likelihood of cloudbursts and flooding in future.

  
  Furthermore, more and more water wells in Høje Taastrup are being closed as a consequence of reduced water consumption.

  
  As a result, the water table in the eastern part of the municipality has risen from five meters to now only 30 centimetres below ground surface since the 1970s.

  
  Høje Taastrup Fjernvarme's stake in the project is driven by the promise of lower operating costs. And what is more obvious to this end than exploiting the free energy source that is groundwater?

   

  Photo: Høje-Taastrup Fjernvarme

• Extracting energy from groundwater to heat homes

  The groundwater is pumped up and passed through an electric heat pump which recovers the heat from the water. Then, the cooled water is pumped out into the Mølleåen river.

  
  During the process, the temperature of the water falls from 9-12 degrees Celsius to around 4 degrees Celsius.

   

  Høje Taastrup Fjernvarme retrieves groundwater from two wells in the eastern parts of Høje-Taastrup Municipality. The wells were previously used to extract drinking water. However, due to falling water consumption and too much nickel in the water, the wells were discontinued in the 1990s.

  
  The groundwater is retrieved from a depth of around 10 meters. It is 9-12 degrees Celsius when pumped up and sent to the 1.5-megawatt electric heat pump.

  
  The heat pump recovers the energy from the water and produces heat that is distributed through the district heating system. The facility provides heating to around 150 homes.

  
  The temperature of the water drops to around 4 degrees Celsius after it has passed through the heat pump. The cooled water is channelled via an approximately 200-meter-long concrete-lined channel into Mølleåen.

  
  Once the facility is running on full capacity, it will be able to pump around 1.4 million cubic metres of groundwater a year, with the heat pump able to produce around 13,000 MWh a year. This corresponds to 4% of the municipality's district heating consumption. Høje Taastrup Fjernvarme meets 70% of the municipality's heating consumption.

  
  The facility is operated for approximately nine months of a year. During the remaining three months, the district-heating company uses waste heat from a biogas plant, as this is the most financially viable solution during the three remaining months.

  
  The heat pump can be easily turned off and on depending on the price of Høje Taastrup Fjernvarme's other energy supply.

  
  It is expected that more water wells will be discontinued in the municipality in the years to come. Furthermore, the municipality expects that the water table will rise by another 50 centimetres.

  
  The groundwater heat pump system can be scaled up easily. And the municipality and the district-heating company anticipate the deployment of more heat pumps in the coming years.

  
  The head of engineering at Høje Taastrup Fjernvarme, Uffe Schleiss, got the idea for the project. He believes that the system also has potential elsewhere.

• Dry basements and reduced CO2 emissions

  Cheaper and almost fossil fuel free district heating production. Improved aquatic environments and dry basements. With four positive outcomes, Høje Taastrup Fjernvarme has declared the system a win-win-win-win.

  
  When the pumps were first put in operation in January 2019, the very high water table immediately sank by 40 centimetres. The facility is therefore not only considered a success in terms of climate change adaptation. It also means no more wet basements in the area.

  
  Furthermore, heat production is cheap, because it only requires the electricity needed to power the heat pump. And the electricity for this comes from a biogas plant and is therefore sustainable.

  
  During the process, the temperature of the water falls form 9-12 degrees Celsius to 4 degrees Celsius. The cooled water is led out into Mølleåen and is aeriated along the way as it passes along an open channel. Here, the lower temperature and the aeriated water contribute to reduced algae growth and better living conditions for flora and fauna.

• Problem with elevated groundwater solved at no cost

  Høje Taastrup Fjernvarme saw the viability of building the energy plant based on a standard business model.

  
  At no cost, an excessively high water table has been lowered.

  
  The district heating company's total cost of DKK 16 million has gone exclusively to the establishment of the facility that recovers heat from the groundwater.

  
  Although the heat from the groundwater is a 'free energy source', the price of heating for district heating customers has not dropped accordingly. However, it has not increased either, despite increasing energy taxes.

  
  So far, the facility only meets 4% of the district heating demand. This is not enough for the lower price of production to be reflected in the price for end users.

   

  On the other hand, the local residents now have dry basements!
  It is financially viable for the facility to operate for approximately nine months a year. This means the costs of establishment will have been recovered in 11 years.

• A simple project with many stakeholders

  Establishing a heat pump that runs on water sounds simple enough. However, the Danish Energy Agency, several local-government divisions, the distribution system operator Radius, DTU (Technical University of Denmark) and Smart Cities Accelerator have all been involved in various phases of the project.

  
  The facility has been several years in the making.

  
  First, the Danish Energy Agency had to provide dispensation to establish the facility in an area designated for CHP. A similar project today could proceed without dispensation.

  
  The project also needed the approval of the environmental division at Høje-Taastrup Municipality and, then, of the parks division. The neighbours had to be briefed and reassured. Furthermore, electricity connections had to be established.

  
  Neither of these parts of the process took a disproportionately long time to complete, but together the whole process took a long time.

  
  The scientific environments did not spend any 'billable' time on the project. Their contribution was to take part as experts, which they did concurrently with their ordinary work.

• Minor problems - nothing serious

  When you embark on an entirely new solution, you have to accept that you can't know everything beforehand. That's how Høje Taastrup Fjernvarme sees it. You have to accept some risk.

  
  "We experienced minor obstacles along the way, but no major barriers," said Uffe Schleiss, head of engineering at Høje Taastrup Fjernvarme.

  
  "We hear from many other places in Denmark, that they are nervous. Nervous about causing contamination and soil subsidence if they extract too much groundwater."

  
  Uffe Schleiss points out that you have to be prepared for some degree of 'technological conservatism' - these projects need to go through a process of maturation.

  
  You also have to accept that you can't know everything before you embark on a project like this. So you have to accept some risk.

  
  Amongst other things, Høje Taastrup has had problems with leaches and iron in the water. Both these problems were solved by moving the wells.