Applications Manual Bosch Geothermal Heat Pumps
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Bosch Thermotechnology Corp.
Data subject to change
Most soil is a combination of ne and coarse grain
(Table 23). A sieve analysis can be used to determine the
percentage of each so that a weighted average can be
developed to nd an overall conductivity. Moisture content
is a major factor, but sand or clay never needs to be
heavily saturated to provide good conductivity.
The thermal properties for typical rock are shown (Table
24). There is typically a wide variation in performance.
Because of its high porosity, rock generally has lower
performance. The 80% range is more conservative and is
recommended without more detailed information.
Thermal Properties for Typical Rock
Rock Type
% Occurance
in Earth's
Crust
k - All
Ther. Con.
Btu/h•ft°F
K - 80%
Ther. Con.
Btu/h•ft°F
C
Spec. Heat
Btu/lb-°F
Density lb/ft³
(k/
C)
Ther. Diff. ft²/
day
Igneous Rocks
Granite (10% Quartz)
10.4
1.1 - 3.0
1.3 - 4.9
1.5 - 2.1
0.21
165
0.9 - 4.3
1.0 - 1.4
Granite (25% Quartz)
10.4
1.1 - 3.0
1.3 - 4.9
1.5 - 2.1
0.21
165
0.9 - 4.3
1.0 - 1.4
Amphibolite
42.8
1.1 - 2.7
0.8 - 2.8
1.5 - 2.2
0.9 - 4.47
0.12
175 - 195
160
1.1 - 4.7
Andesite
42.8
1.1 - 2.7
0.8 - 2.8
1.5 - 2.2
0.9 - 4.47
0.12
175 - 195
160
1.1 - 4.7
Basalt
42.8
1.2 - 1.4
0.17 - 0.21
180
0.7 - 0.9
Gabbro (Cen. Plains)
42.8
0.9 - 1.6
0.18
185
0.65 - 1.15
0.85 - 1.5
Gabbro (Rocky Mtns.)
42.8
1.2 - 2.1
0.18
185
0.65 - 1.15
0.85 - 1.5
Diorites
11.2
1.2 - 1.9
1.2 - 4.7
0.22
180
0.7 - 1.0
Grandiorites
11.2
1.2 - 2.0
0.21
170
0.8 - 4.3
Sedimentary Rocks
Claystone
1.1 - 4.7
Dolomite
0.9 - 3.6
1.6 - 3.6
0.21
170 - 475
1.1 - 2.3
Limestone
0.8 - 3.6
1.4 - 2.2
0.22
150 - 475
1.0 - 4.4
Rock Salt
3.7
0.20
130 - 435
Sandstone
1.7
1.2 - 2.0
0.24
160 - 470
0.7 - 4.2
Siltstone
0.8 - 1.4
Wet Shale (25% Quartz)
4.2
0.6 - 2.3
1.0 - 4.8
0.21
130 - 165
0.9 - 1.2
Wet Shale (No Quartz)
4.2
0.6 - 2.3
0.6 - 0.9
0.21
130 - 165
0.5 - 0.6
Dry Shale (25% Quartz)
4.2
0.6 - 2.3
0.8 - 4.4
0.21
130 - 165
0.7 - 1.0
Dry Shale (No Quartz)
4.2
0.6 - 2.3
0.5 - 0.8
0.21
130 - 165
0.45 - 0.55
Metamorphic Rocks
Gneiss
21.4
1.0 - 3.3
1.3 - 2.0
0.22
160 - 175
0.9 - 1.2
Marble
0.9
1.2 - 3.2
1.2 - 1.9
0.22
170
0.8 - 1.2
Quarzite
3.0 - 4.0
0.20
160
2.2 - 3.0
Schist
5.1
1.2 - 2.6
1.4 - 2.2
170 - 200
Slate
0.9 - 4.5
0.22
170 - 475
0.6 - 0.9
Tab.24 Thermal properties for typical rock
Courtesy of American Society of Heating, Air-conditioning and Refrigeration
Engineers Inc., www.ashrae.org.