Mijnwater project in Heerlen, The Netherlands
The municipality of Heerlen started this project in 2005 to investigate whether anything could be done with the groundwater in the flooded mine galleries. The mine water initiative in Heerlen is a geothermal project originating from the European Interreg IIIB NWE programme and the 6th Framework Programme project EC-REMINING-lowex.
The Mijnwater project was built as a 4th generation District Heating and Cooling network. In the winter, warm water of 28°C was fed from the mine into the grid to deliver warmth, while in the summer cool water of 16°C from a shallower cool source was distributed. This was a ‘4th Generation’ grid in the sense that it used a low temperature heat source (or high temperature cooling), and also that it distributed the heat or the cold from a central point to the customers. This grid started by serving one large office building (national statistics bureau CBS) and a social housing project in Heerlen. Several utility buildings were connected, but the first installations slowly exhausted the geothermal source, limiting its scalability. In 2012, the upgraded and new system tried to counter the limitations by integrating the storage of heat from buildings for other moments in time or locations. Since then, the grid is able to exchange heat and cold between all customers, simultaneously, while the mine water system is used to store heat and cold. Mijnwater became a so-called cold network based on the combined heating and cooling (CHC) configuration with the following five ambitions:
1. Closing the energy loop: An optimized system allowing exchange of heat and cold between end users. To prevent waste, energy exchange occurs first at the scale of the building, then within the neighbourhood and finally at the city level.
2. Using low-graded sustainable sources: Energy sources can be classified according to their application opportunities. The high graded sources have the potential to be used twice or more, like first serving industrial processes and the waste flow for heating buildings. In CHC, the supply is matched with the requested quality level of the demand.
3. Decentralized & demand-driven energy supply: Circulating energy within the system only when and where needed, as close as possible to the end-user.
4. An integral approach of energy flows at the city scale: Connecting heating and cooling to other energy flows (power grid, hydrogen conversion, solar plants, etc.) within the city, to avoid energy waste across sectors and reduce peak loads.
5. Local sources as a priority: Avoiding big investments and energy losses in transport, while stimulating the local economy.
In 2020, Mijnwater supplied sustainable heat and cold to more than 400 dwellings and 250,000 m2 of commercial buildings. It gives a major contribution to the sustainability of the built environment in Heerlen and Parkstad-Limburg more. The project is positioning the city of Heerlen as an innovative green tech region in the field of thermal smart grids. The goal is to connect 30,000 homes and offices in Parkstad by 2030. Mijnwater is using a cluster approach to transform the concept from a mine water pilot project into a modern, intelligent, and sustainable hybrid energy infrastructure. The geographically dispersed local cluster grids are supported by a mix of local sustainable resources, which are supplied by the mine water grid (backbone) and mine water reservoir. Energy exchange will be realized between buildings by means of local cluster grids and between the cluster grids through the existing mine water grid.
Buildings are no longer just an energy consumer but also an energy supplier. A building that extracts hot water (e.g. 27 °C) for heating from the hot pipe of the cluster grid returns cold water back to the cold pipe of the cluster grid (< 15 °C). Other buildings connected to the grid for cooling can instantly use this cold water. Heating and cooling of the buildings can occur passively and/or actively by using heat pumps. This depends on the available temperatures in the cluster grid (cold 8–20˚C; heat 27–50˚C) and the requested release temperatures of the building (cold 5–18˚C; heat 30– 50˚C). At the end user location, heat pumps adjust the supply temperature to the necessary temperatures for heating or cooling. A special booster heat pump produces hot tap water at delivery.
Solar collectors and other heat generators can deliver additional heating and cooling, like a bio-CHP, which can raise the supply temperature for heating up to 50– 55 ˚C. To achieve high exergy efficiencies by maximizing passive (re-) use of heat and cold and by raising the heat pump efficiencies up to a COP of 7(+), a boiler house is designed.
The production wells (HH1 and HLN1) supply the shortage of heat and cold to the mine water backbone. The surplus of heat and cold will be stored in the mine water reservoir through the injection wells (HH2 and HLN2). The current return/injection well (HLN3) will be out of order and only be used in case of exceptional situations.
The capacity of the mine water system is finite, if the heat-, cold extraction and infiltration is not balanced on a yearly basis. To ensure that the extracted hot (27– 50 ˚C) or cold water (8–20 ˚C) from the cluster grid is cooled down (< 15 ˚C) or heated up (> 29 ˚C) sufficiently before injection in the mines, a temperature condition is included in the contract with the end users.
For realizing the objectives of the Sustainable Structure Plan of Heerlen a combination of mine water with other renewable energy sources such as biomass and/or solar energy and waste heat is necessary. All these energy sources are locally situated and will be connected to the nearest cluster grid to supply their heat and cold to the corresponding cluster and through the mine water backbone to other clusters.
The existing mine water return pipe will be used for additional supply and disposal of hot or cold mine water. At the cluster grid a cluster installation with booster pumps for energy exchange between the mine water and cluster grid are installed. Sophisticated injections valves are applied at the hot and cold injection wells and in the near future all wells become bidirectional for further capacity enlargement, back-up and smart production and injection of mine water.
The Minewater system is fully automatic and demand driven with three levels of control. All buildings (first level) are connected to a cluster network (second level). Several clusters are connected to the mine water backbone and reservoir (third level). At each level (building, cluster, mine water) there is a net heat or cold demand. The buildings determine the demand of the cluster. The cluster provides what the buildings demand. The clusters determine the demand of the mine water backbone. The mine water backbone and mine water wells provide what the clusters demand.
Exchange at the interface between the levels takes place with autonomous substations (MI = Minewater Installation). Each level works with another independent process control parameter. To show how it works a typical process situation is shown in the artist impression of Figure 78.
