Frequently asked questions
The most important answers about the grouting of geothermal probes
Damages of geothermal drillings are actually caused by non professional settings of the probes or difficult geological or hydrogeological conditions.
With the professional use of grouting materials unfavourable geological conditions can possibly be offset. (For example safe closure of the borehole, in which pressurized ground water rises)
But there are some geological conditions, where the use of borehole heat exchangers is not recommended. If there are difficulties in the construction phase, it should be considered carefully, if the conditions can be offset with professional techniques or if the drilling should be discontinued.
The bigger drilling space has to be grouted dense and durable to secure the pipes, to ensure a high thermal conductivity from the rocks to the pipes and the circulating water-glycol liquid, and also to stabalise the borehole wall.
Due to the ground water protection, surface water needs to be prevented of contaminating in to the ground water and the different levels of ground water need to stay separated.
(Note: This does not apply to Bavaria, there are only drillings to the first aquifer allowed.)
A grouting material of high quality prevents with its environmental compatibility, the introduction of harmful substances into the ground water or the soil. It guarantees with its long term stability (against effects of frost in the probes or cement invasive substances in the ground water) a good connection of the probe to the soil/rock. The introduction of surface water is prevented and the protection of the ground water is assured. The use of thermally enhanced grouting material increases the efficiency of the installation, due to a lower resistance between the borehole wall and the probes. This ensures an improved heat transfer.
The thermal conductivity describes a characteristic of the material. The unit of measurement is expressed in Watt per meter/kelvin (W/m*K) and describes how the thermal energy is transferred through the substance.
With high thermal conductivities the thermal energy is transferred very effectively. This leads to a great efficiency of the geothermal installation and ensures a good transfer of the heat while heating and a fast discharge into the surrounding ground while cooling.
The borehole resistance is a value, measured with the Thermal Response Test (TRT), which is carried out on site in a borehole heat exchanger. The borehole resistance is composed of the geometry of the probe, the thermal characteristics of the grout and the impact of disturbances (possibly present ground water). Therefore it is recommended to use thermally enhanced grouting materials, because it lowers the borehole resistance.
The frost thaw stability is important for the grout in regards to the operation of the system. Possible effects of frost are caused by the circulation of under cooled (below 0 C) water-glycol-mixture and not by the frost on the surface of the ground.
(Note: The geothermal pipes are laid frost resistant below the natural level of frost) Frost thaw stable materials like Fischer GeoSolid are not damaged by the temperatures in the probes, caused by frosting excessive water or ground water in the pores. This characteristic is important to achieve a durable and stable grout in the borehole heat exchangers.
The material has to be mixed with a proper mixer, continuously or in batches. An optimum result is achieved with the use of a colloidal mixer.
Additional grout has to be re-injected, if the suspension in the borehole subsides due to joints or ground water flows. It can be prevented by using a high quality grouting material with the necessary high suspension density for example the Fischer GeoSolid products. Also it helps to mix the grouting material homogeneously.
First the suspension is mixed in a mixer with one or more injection hoses or rods and then the suspension is pumped into the borehole. This is done with the contractor procedure from the bottom to the top.
This shall ensure that possible present ground water is displaced to the top or the sides and the whole borehole is grouted with the same density. The suspension density is controlled while the grouting procedure. The grouting is completed, when the suspension density is the same in the suspension coming up to the surface as the density of the suspension that is being pumped into the borehole.
Damages of geothermal drillings are actually caused by non professional settings of the probes or difficult geological or ...
The bigger drilling space has to be grouted dense and durable to secure the pipes, to ensure a high thermal conductivity from the ...
A grouting material of high quality prevents with its environmental compatibility, the introduction of harmful substances into the ...
The frost thaw stability is important for the grout in regards to the operation of the system. Possible effects of frost are ...
Fischer Spezialbaustoffe GmbH developes and produces thermally enhanced grouting/ backfilling material for borehole heat exchangers.
The products Fischer GeoSolid are characterised by a high thermal value, a proven frost-thaw-stability as well as optimum physical properties. Furthermore Fischer GeoSolid 240HS is suitable for the use in sulphate bearing ground waters.