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Simulation of geothermal borehole fields with regeneration

Active regeneration of the ground in summer can significantly increase the efficiency of geothermal systems and reduce investment costs.

Influence of regeneration on the size of the borehole field

Regeneration in geothermal fields means that over the year, not only heat is extracted from the ground, but for example, in summer, heat is also injected back into the ground. This is often achieved through the provision of cooling. Regeneration can mitigate the cooling of the soil over the years and thus has a decisive influence on the design. The calculation of the fluid temperatures of geothermal is determined using three load components:

  • Net base load: average net heat demand over the year
  • Max. periodic monthly load due to seasonal temperature differences
  • Peak load (at the time of the lowest outdoor temperature)

Each of these load components is multiplied by a thermal resistance, from which the temperature response of the probe is then determined through summation. The arrangement of the probes or the probe spacing exclusively influences the temperature response due to the net base load. The resistance of the base load increases as the ratio of probe spacing to probe length decreases, becoming the dominant design factor. However, if the probe field is actively regenerated, the net base load decreases. The influence of the base load and thus the probe spacing decreases until a regeneration rate of 100% is reached, where over the year, the same amount of heat is extracted from the ground as is injected. At this point, the influence of the probe spacing disappears entirely, and the probe field can be significantly downsized. A noticeable reduction in the probe field size is achievable even with low regeneration rates of 10% or 20%.

In the nPro tool, the number and arrangement of geothermal probes can be optimized, and extraction temperatures can be simulated.

Regeneration of geothermal fields with solar thermal collectors

The regeneration of geothermal fields through solar thermal collectors is an innovative method aimed at increasing the efficiency and performance of geothermal plants. This technique uses solar energy to raise the temperature of the soil or water in geothermal reservoirs. This increases the heat storage capacity of the subsurface and enhances the capacity of the geothermal field. The use of solar thermal collectors for regenerating geothermal fields can be particularly effective in summer when there is an excess of solar heat. Integrating solar thermal collectors for the regeneration of geothermal fields can offer various benefits: Active regeneration can increase the exit temperature of the probes during the heating period, leading to more efficient heat pump operation. Furthermore, regeneration allows for a reduction in the required number of probes, probe length, or probe spacing. This often results in substantial savings in investment costs.

Planning probe fields for heating networks

Geothermal fields offer an efficient way to supply heat to heating networks as they represent a constant and sustainable energy source. The natural heat within the ground enables a continuous heat extraction, which is independent of external influences such as weather conditions, ensuring reliable supply. Additionally, compared to conventional heat sources, geothermal fields are an environmentally friendly option as they are renewable and cause minimal CO₂ emissions. Designing probe fields for heating networks requires a precise consideration of temperature fluctuations in geothermal fields since they affect temperatures in the heating network, especially in 5GDHC networks. During the heating period, geothermal probes extract heat, leading to a cooling of the surrounding soil and reducing the efficiency of the probes. Planning must consider this decrease in heat yield over the year to ensure reliable heat supply.

Geothermal sources for heat pumps

The heat pump is an efficient and environmentally friendly heating technology, but its efficiency greatly depends on the temperature at which it absorbs heat (source temperature). During the winter months, the air temperature can drop significantly, which can affect the performance of an air-to-water heat pump. However, using geothermal heat allows for a reliable, higher temperature during winter. This helps to increase the efficiency of the heat pump while simultaneously reducing its load. Geothermal probes provide a more stable heat source, independent of the temperature fluctuations of the ambient air, thereby optimizing the performance of the heat pump.

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