Introduction
Test site
Borehole | Type | Number GSHE | Installation depth | Grouting | Drilling technique |
---|---|---|---|---|---|
#3 | Helicoidal GSHE | #04 | 8 m (● 15 m) | Sand–bentonite mixture | Auger |
#4 | Helicoidal GSHE | #02 | 8 m (● 15 m) | Sand–clay powder mixture | Auger |
#5 | Helicoidal GSHE | #01 | 8 m (● 15 m) | In situ material | Enlarged easy drill |
#6 | Helicoidal GSHE | #03 | 8 m (● 15 m) | Building sand | Auger |
#1 | – | Undisturbed underground temperature (UT) | 5 m | In situ material | Enlarged easy drill |
Materials and methods
Helicoidal GSHE + sensors
Parameter | RAUGEO Helix | RAUTITAN New Helix |
---|---|---|
Material | PE-Xa | Pe-Xa/AL/PE |
Pipe dimension | 25 × 2.3 mm | 25 × 3.7 mm |
Inner tube diameter | 20.4 mm | 17.6 mm |
Pipe length | 40 m | 40 m |
Pipe volume | 13.1 dm3 | 9.7 9.7 dm3 |
Outer GSHE diameter | 360 mm | 260–275 mm |
GSHE pitch | 90–95 mm | 700–790 mm |
Drilling technique | Auger (+ casing) | Enlarged easy drill or standard auger |
Drilling diameter | 420 mm | 356 mm (inner easy drill) 390 mm (Auger) |
Density | 0.94 g/cm3 | 0.9832 |
Thermal conductivity | 0.40 W/m−1 K−1 | 0.43 W/m−1 K−1 |
GSHE height (construction condition) | 3 m | 15 m (8 m*) |
Construction depth | 1.2–4.2 m | 0–15 m |
Grouting | Excavated material | Thermal enhanced |
Number GSHE | #01 | #02 | #03 | #04 | – | |
---|---|---|---|---|---|---|
Borehole | #5 | #4 | #6 | #3 | #1 | |
Sensors | Sensor type | Installation depth | Installation depth | Installation depth | Installation depth | Installation depth |
TR1 | Temperature sensors—inlet pipe | 0.0 m | 0.0 m | 0.0 m | 0.1 m |
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|
TR2 | 4.0 m | 4.1 m | 4.0 m | 3.9 m |
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| |
TR3 | 8.0 m | 8.0 m | 8.0 m | 8.0 m |
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| |
TS1 | Temperature sensors—GSHE centre | 2.1 m | 2.0 m | 1.9 m | 2.0 m |
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|
TS2 | 6.0 m | 6.0 m | 6.0 m | 6.0 m |
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| |
F1 | Moisture sensors—GSHE centre | 0.1 m | 0.1 m | 0.1 m | 0.1 m |
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|
F2 | 4.0 m | 4.0 m | 4.0 m | 4.0 m |
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| |
F3 | 7.9 m | 8.0 m | 8.1 m | 8.1 m |
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| |
TU1 | Undisturbed underground temperature (UT) |
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|
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|
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|
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| 0.0 m |
TU2 |
–
|
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|
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|
–
| 1.0 m | |
TU3 |
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|
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|
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|
–
| 2.0 m | |
TU4 |
–
|
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|
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|
–
| 3.0 m | |
TU5 |
–
|
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|
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|
–
| 4.0 m | |
TU6 |
–
|
–
|
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|
–
| 5.0 m |
Installation
Drilling
Grouting
Number GSHE | #04 | #02 | #01 | #03 |
---|---|---|---|---|
Borehole | #3 | #4 | #5 | #6 |
Mixture | 15 vol% bentonite; 85 vol% sand | 30 vol% clay powder; 70 vol% sand | 15 vol% clay powder; 85 vol% sand | 100 vol% sand |
USDA analogue | Loamy sand | Loamy sand | Sand–loamy sand | Sand |
Produced amount | ~ 2.1 m3 | ~ 2.1 m3 | ~ 2.1 m3 | ~ 2.1 m3 |
Costs per tonne (without VAT and transport) | 62.70 € | 30.05 € | 22.88 € | 15.71 € |
Thermal response test as power source
Results and discussion
Installation
Sensor’s response
Number GSHE | #01 | #02 | #03 | #04 |
---|---|---|---|---|
Borehole | #5 | #4 | #6 | #3 |
Mixtures | In situ | Clay powder | Sand | Bentonite |
Test duration | 72 h | 72 h | 72 h | 72 h |
Temperature inlet flow (IF) | 40.12 °C | 39.46 °C | 38.76 °C | 39.81 °C |
Temperature return flow (RF) | 37.98 °C | 37.61 °C | 36.90 °C | 37.80 °C |
TR1 (t = 72 h) | 34.1 °C | 31.6 °C | 32.8 °C | 32.1 °C |
TS1 (t = 72 h) | 31.1 °C | 28.4 °C | 26.9 °C | 26.3 °C |
TR2 (t = 72 h) | 27.8 °C | 31.2 °C | 29.8 °C | 28.0 °C |
TS2 (t = 72 h) | 26.1 °C | 26.5 °C | 25.0 °C | 23.9 °C |
TR3 (t = 72 h) | 29.3 °C | 24.9 °C | 29.0 °C | 28.6 °C |
TR3/IF | 73.0% | 63.1% | 74.8% | 71.8% |
ΔT (IF − TR3) | 10.82 °C | 14.45 °C | 9.76 °C | 11.21 °C |
TR3/TR1 | 85.9% | 78.8% | 88.4% | 89.1% |
ΔT (TR1 − TR3) | 4.8 °C | 6.7 °C | 3.8 °C | 3.5 °C |
TR2/IF | 69.3% | 79.1% | 76.9% | 70.3% |
ΔT (IF − TR2) | 12.32 °C | 8.26 °C | 8.96 °C | 11.81 °C |