The energy stored underground is brought to the surface by means of special plastic pipes filled with a brine fluid consisting of water and antifreeze. A heat pump then uses the extracted energy for heating and cooling purposes.
1. Creating the boreholes
Hydraulic drilling rigs are used to drill the boreholes to the required depth. Depending on the geological conditions, one of the two following methods is used:
a) Down-the-hole drilling method
In solid rock, blocky or coarse gravel soils, the holes are drilled to the required depth using the down-the-hole drilling method. Compressed air generated by a compressor flows through the drill pipe to the hammer. This uses a high number of strokes (about 600 strokes per minute) to crush the material.
The cuttings are then brought to the surface through the annular space using compressed air.
An auxiliary pipework system is installed in the loose rock, also known as the overburden, at the same time as the drill pipe. This prevents the borehole from collapsing and ensures the safe installation of the borehole heat exchangers after the borehole has been finished.
b) Direct hydraulic drilling method
With the direct hydraulic drilling method, a thick drilling fluid with a high specific weight is used instead of an additional auxiliary pipework system to stabilise the borehole wall.
Due to the rotating motion of the drill pipe and the high specific weight of the drilling fluid, a thin film of clay is pressed against the borehole wall. This is called a filter cake. The circulating drilling fluid creates excess pressure inside the borehole. This ensures that the borehole wall remains stable, even without an auxiliary pipework system.
The drilling fluid is sucked out of the flush tank by a pump and pressed downwards through the drill pipe. The drilling tool, e.g. a roller bit or wing bit, is screwed onto the lower end of the drill pipe. The pressurised drilling fluid helps the drilling tool loosen the in-situ soil and convey it upwards through the annular space. Sedimentation of the drilled material takes place inside the sedimentation basin. This process is repeated, creating a flushing circuit.
2. Installing the borehole heat exchangers
The borehole heat exchangers are installed after sinking the borehole and extracting the drill pipes. As a rule, two plastic U-pipes are used. These are also called double U-pipe heat exchangers.
3. Grouting the borehole heat exchangers
In order to maintain the heat flow from the ground to the brine-filled plastic pipes, the borehole is filled with a special heat-conducting grouting material from the bottom up. This sealing process also prevents the individual groundwater horizons from being connected.
4. Horizontal connection
The horizontal connection is the connection between the heat pump inside the building and the underground borehole for the borehole heat exchanger. Here we take care of the requisite distribution system and the connecting pipes that have to be laid to the borehole heat exchanger. Our trained employees then fill the pipes with the heat-transmitting medium and carry out a pressure and flow test.
Following a successful start-up operation, your new energy source will be handed over to you ready for use.
Any more questions? Contact us for information, further details or an individual quote.