Environmental Engineering Reference
In-Depth Information
Table 9.4 shows guidelines of a possible heat withdrawal for smaller systems
and different types of soil. In order to keep a long-term balanced situation, an an-
nual amount of withdrawn heat between 180 and 650 MJ/(m a) must not be ex-
ceeded - with exclusive recovery by solar energy penetrating the surface of the
earth and geothermal energy flowing up - depending on the individual subsoil
conditions /9-4/.
The values shown in only give very rough guidelines. A more exact definition
of the specific heat withdrawal capacities can be calculated if the thermal subsoil
conditions are known (Fig. 9.11). For larger ground probe systems only calcula-
tions are possible for the system design in order to determine the required amount
and length of ground probes. These calculations can be done by existing computer
programs. For difficult cases a simulation with numeric models should be carried
out, especially if the influence of flowing groundwater has to be considered. In
order to obtain reliable input parameters for such calculations, the Thermal Re-
sponse Test was developed. It allows the determination of thermal subsoil pa-
rameters on site.
80
Data according to VDI 4640
70
60
Data with groundwater flow
50
Data according to VDI 4640
40
Data without groundwater flow
30
20
Data according to VDI 4640
10
0
1
1.5
2
2.5
3
3.5
4
Subsoil heat conductivity in W/(m K)
Fig. 9.11
Exemplary specific heat withdrawal capacities for small ground probe installa-
tions (calculated for a detached family house requiring 10 kW for heating, on the basis of 2
ground probes and 1,800 hours at full load per year, excluding hot water; see /9-2/)
The bore method to sink the ground probes is dependent on the expected
ground layers and the available space /9-4/.
−
In lose rock boreholes can be sunk with a hollow drill screw. The bore material
is transported and/or displaced.
−
When drilling with jetting methods, that can also be applied in lose rock; the
drilling fluid continuously carries the bore material out through the ring section
from the deepest point of the borehole. Additionally, the drilling fluid pumped
into the borehole also stabilises the borehole wall and maintains it in line with
the diameter of the bore. It also cools and greases the bore tools and seals off
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