Geothermal energy, extracted from forty 170 m (573 ft.) deep boreholes, is being used to heat and cool the newly constructed 11 000 m3 municipal office in the city of Lund in southern Sweden. The formation includes both soft and hard layers of rock.
The complicated drilling project was successfully carried out in 2013, despite the fact that the surrounding downtown buildings were at risk if the formation was pressurised. Thanks to Wassaras water-powered DTH hammer, drilling passed through the different formation layers without incident.
The Kristallen building
The Kristallen municipal office in Lund, Sweden, is an extremely energy efficient building. It is heated and cooled by geothermal energy extracted from 40 boreholes. The heat pump supplies the 11 000 m3building with all the heating energy required, neither boilers nor district heating are necessary. In total, the system provides the building with about 0.5 MW of heating effect and 1 MW of cooling.
First challenge: Drilling in alternate layers with hard and loose formations
Geological investigations indicated that the formation consisted of both hard and loose layers. The 170 m (573 ft.) deep boreholes would need casings to be installed during the first 80 m (270 ft.) of drilling. Furthermore, drilling with conventional equipment would not be possible.
Second challenge: Urban historically-rich environment
Another challenge was posed by the location of the new office, which is downtown in the city of Lund. A number of surrounding buildings could easily be damaged if the formation was pressurised, including an adjacent railway station and a private housing estate. This meant air-powered drilling was out of the question.
The Wassara way
Wassara DTH hammer drilling is powered by water at up to 180 bar delivery pressure. When the water leaves the drill bit, the pressure drops considerably and reaches the state of hydrostatic pressure. The flush velocity is, however, still adequate to bring any cuttings to the surface and to clean the borehole.
This lowers the risk of pressurising the formation to a minimum. The soft formation is not at risk and cannot interfere with or cause severe damage to the surrounding infrastructure. And thanks to a specially designed water sedimentation arrangement, the drilling water was approved for disposal in the public wastewater system.