The Mijnwater project was initiated and built by the municipality of Heerlen as a 4th generation District Heating and Cooling network (4DHC). The idea was to use warm water in an abandoned and flooded local coal mine as a sustainable source. In the winter, warm water of 28ºC was fed from the mine into the grid to deliver warmth, while in the summer cool water of 16ºC 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 warmth 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. In 2013, the grid was upgraded to a fully functioning 5th Generation Heating and Cooling grid (5GDHC). The important new feature was that from that time 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 was privatized in 2013, and Mijnwater BV was established with the municipality of Heerlen as 100% shareholder.

The last step in the original design of the Mijnwater system is still being implemented. Without affecting required comfort levels, it is still possible to optimise the exact timing of demand from buildings. The buildings themselves have a thermal mass and can store warmth for some time. The water in the grid itself can also be used to store heat for short periods. As an example, large buildings could in principle be heated more slowly by starting slightly earlier than requested by the thermostat, to avoid a morning peak from all large office buildings starting their working day at exactly the same time.

In September 2018, the Limburgs Energie Fonds (LEF) of the Province of Limburg became the owner of the company, and a new governance structure is being considered in light of a significant scale-up of the business. Facing strong growth in demand for the Mijnwater system in the Parkstad region and beyond, Mijnwater is exploring a number of options to fund this forecasted growth.

Mijnwater BV plans to invest 130 million euros to 2025 and 300 million euros to 2030 for the connection of approximately 30,000 homes. The energy transition of the entire Parkstad Limburg (a region consisting of seven former mining towns in the southeast of the province) until 2050 requires 1.5 billion euros.

The main result Mijnwater BV aims to reach with the investments (€1.6m) from the HeatNet NWE project is to enclose the industrial waste heat in this area and find more heat sources at building level, which would mean that the 5GDHC system could operate more efficiently, and therefore less electricity would be needed for heating and cooling. The ultimate goal is to connect the entire Parkstad Region to the network before 2050.