If you have selected a system with a brine/water heat pump, the page heat source appears with the parameters for a geothermal probe.

How to define the parameters of the geothermal probe(s):

Heat pump

1. The power consumption of the HP on the cold side (also called “cooling capacity”) is taken from the data sheet of the selected HP. You can only modify it by selecting a different heat pump under heat pump.

Brine pump

2. Enter the brine pump’s rated power. If the selected heat pump does not have a removable brine pump with a known rated power, it is imported from the database and cannot be edited here. This rated power has a decisive impact on the simulation result SPF of the heating system part.

3. Enter the flow rate if the latter cannot be taken over from the heat pump data.

4. Enter the % Glycol in the brine.

Soil

5. Enter the undisturbed ground temperature, the effective temperature of the surrounding ground $T_{ER,inf}$. This is usually between 10 and 15 °C. This temperature is averaged over the entire probe length and (in the upper ground layers) seasonal temperatures. It thus refers to the undisturbed ground and not ground cooled by geothermal probes or geothermal collectors. The deeper the borehole is, the higher the local and seasonally averaged temperature of the undisturbed ground will be. See VDI guideline 4640.

Geothermal probe

6. The borehole diameter is crucial for the simulation with the help of the geothermal probe model. 150 mm is a typical standard value. The effect of the borehole diameter can be seen in the results charts:

   • The larger the borehole diameter is, the smaller the borehole resistance, and the closer the probe supply temperature is to the ground temperature (near the probe).

   • The smaller the borehole diameter is, the greater the borehole resistance, and the less the set extraction power can be used.

7. Select a construction type of the geothermal probe:

   • Double U-pipes or

   • Single U-pipes.

8. Infill type for filling in directly around the geothermal probe, see VDI guideline 4640. There is:

   • simple grouting

   • thermally enhanced filler

Length of the borehole heat exchanger

9. Enter the specific extraction rate and the maximum drilling depth or modify the default values.

10. The required heat probe length is calculated. (See below for calculation details.) Whenever you modify the specific extraction power or select a different heat pump, the required probe length is recalculated.

11. Click on the sizing button to distribute the required probe length over the number of boreholes by the rule of three. Once the boreholes are correctly sized in line with the specific extraction power as specified in VDI 4640, no sizing messages appear. If the boreholes are not correctly sized in line with the project data, a warning on over- or undersizing appears in the messages field.

    If you modify the maximum drilling depth, the number of boreholes, and the depth per hole is recalculated.

    An experienced planner may depart from the probe length calculated here. The latitude available can be quickly and simply calculated by carrying out several simulations.

Note: You have selected a heat pump that fits the borehole (depth, diameter), and the geothermal probe (extraction rate). If you change the borehole subsequently, you need to select a different heat pump! Or at least, you should check the power of the heat pump.

Also see: Geothermal probe – calculation details.