GGU-STRATIG: Generate ground source heat utilisation table to VDI 4640

When exploiting the subsurface by means of borehole heat exchangers, the design of borehole heat exchangers for systems with heat pump outputs up to 30 kW and used in heating mode only should be carried out using specific heat extraction values (in W/m) from Table 2 of VDI 4640 Part 2. A corresponding table for entering the specific heat extraction of the drilled strata is implemented in GGU-STRATIG. Based on the input the program determines the heat extraction capacity for each stratum.

If you want to display a ground source heat utilisation table adjacent to the existing borehole, click the "Ground heat (VDI 4640)" button in the general editor box for tables. The following dialog box opens:

In the "Ex_Geothermal energy.bop" example file the ground source heat table is shown adjacent to hand percussion bore KRB 6. If a new VDI table is created and a number of boreholes are available, the borehole with the depth data for adoption in the table can be selected using the drop-down menu in the dialog box. Define the position of the table as the distance from the right edge of the selected borehole. The value of x in the base data is adjusted accordingly.

If a brand new table is created the values for the specific heat extraction capacity can initially all be defined as a default value for all layers. Select the annual operating hours "1,800 h/a"or "2,400 h/a" for evaluating the heat extraction capacity. The strata thicknesses can also be activated as an additional table column for use in the visualisation.

If the dialog box is then exited by pressing "OK", the name in the base data and the column headings are adjusted automatically. The specific heat extraction capacity of the soils in your borehole can be adjusted using the "Edit values" button in the general editor box for tables.

Once the data has been edited ensure that the "Replace existing specific heat extraction values by default values" check box is deactivated when the dialog box "Ground heat (VDI 4640)" shown above is opened once more. If you open the dialog box again and exit by pressing "OK", all of the previously adjusted values will be reset to the defaults.

By pressing "Tab. 2, VDI 4640" it is possible to review the values for individual rocks given in 'Tabelle 2. Mögliche spezifische Entzugsleistungen für Erdwärmesonden' (Table 2. Possible specific extraction values for borehole heat exchangers), VDI 4640 Part 2, September 2001.

All previously entered values can be multiplied by a factor by pressing the "Edit values" button in the dialog box above.

The values in the "Thickness [m]" (if activated) and "Heat extraction [W]" columns in the table shown on the screen are determined automatically by the program. The ground source heat utilisation table also includes a total row, giving the extraction capacity for the entire thickness of the borehole.