The Hague, Netherlands


The City of The Hague has developed an innovative energy concept that consists of a seawater central supply unit with a heat exchanger and heat pump unit that uses the nearby sea as a temperature source. The Hague and Vestia Housing Corporation have partnered with Deerns to implement this energy source in the reconstruction of 750 of the 3,000 dwellings located within Duindorp. Duindorp lies along the North Sea Coast and consists mainly of small family houses built between 1915 and 1931, formerly occupied by fishermen. The seawater central supply unit is connected via a distribution grid to the individual houses. Each housing unit will have an individual heat pump for further heating.

What is it?

A system that extracts seawater and then processes the seawater either via a heat exchanger or heat pump (depending on the time of year) to supply an entire residential area with space heating and hot water. A central unit is located near the harbor that contains both the central heat exchanger and heat pump. Smaller individual heat pumps are installed in each home for further heating. The energy yield produced by drawing heat from the sea is 1,100%, and that in turn results in a 50% reduction in CO2 emissions. End users do not pay more for this system than a conventional system.

How does it work?

  • The first idea of a seawater plant was brought forward in 1999 by the local energy company ENECO at a workshop organized by CERES (a property development group and branch of the local housing company VESTIA) and the City of The Hague in hopes of finding a way of achieving a carbon neutral city.
  • CERES/VESTIA and the City of the Hague wrote a financing proposal of €1,000,000 and agreed to finance the project themselves, splitting the cost in half.
  • Rules and regulations were discussed in detail and Scheveningen Harbour was selected as an excellent location for the development of a seawater plant.
  • DeernsRaadgevendeIngenieurs, one of Europe's biggest independent technical consultancy firms, was contracted by VESTIA/CERES to develop the project.
  • For the technical details, DEERNS worked together with GTI-West, an engineering company.
  • The seawater plant consists of a heat exchanger and a heat pump. At the end of a distribution network, individual heat pumps are installed in each home to provide space heating, domestic hot water and floor heating.
  • Seawater is extracted in the Harbour by a central unit and then processed either one of two ways:
  • Heat Exchanger:
  • In the summer, when temperature of seawater is more than 11°C, only the heat exchanger is used. The heat exchanger feeds heated water to local grid, drawing enough heat from the seawater to cover residents' need.
  • Heat Pump:
  • In the winter, when the water temperature is less than 4°C, the heat pump is used. Using electricity, the heat pump works to move thermal energy from a cold source to a warmer heat sink. The ammonia heat pump has an output of 2.7 MW and warms the water to approximately 11°C, which is then fed to the local grid. Upon reaching each household, the water is further heated by each home's own heat pump to either 65°C for hot water of 45°C for heating.
  • In 2004, construction began of the 750 houses within Duindorp's 3000 houses that would employ this system. At the same time, construction of the warm water distribution grid began.
  • Construction of the central heat pump facility will be completed by 2008.

Next steps

The construction of the central heat pump facility is still underway. The Hague is looking into the construction of a new 2750 kW wind turbine, making the City carbon neutral. This would mean that all electricity necessary for the City’s central heating installations would be contracted by 100% renewable wind energy. The wind farm would be situated near the seawater plant, in the harbor of Scheveningen.


  • Similar systems can be installed anywhere in the world close to a body of water.
  • City needs space for 10 square meters for extractor and 50 square meters for pumps.
  • City should have a good relationship with housing and energy companies.
  • City needs a sustainable development policy to prove the seriousness of the subject.
  • Helpful to organize innovative technology workshops.