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Geothermal Energy

Science – Society – Technology

Table 4 Thermal routine scheme of one freeze–thaw cycle (FTC) out of a FTC sequence in the pilot experiment with constant hydraulic monitoring

From: Impact of operational temperature changes and freeze–thaw cycles on the hydraulic conductivity of borehole heat exchangers

Pre-conditioning

Freezing state

Thawing state

Cycle-end state

Inlet flow BHEin 3 °C

Inlet flow BHEin − 3 °C

Inlet flow: stop

Inlet flow BHEin 3 °C

Return flow BHEout 3 °C

Return flow BHEout − 2 °C

Return flow: stop

Return flow BHEout 3 °C

Vessel 3 °C

Vessel 3 °C

Vessel 3 °C

Vessel 3 °C

Steady state soil 3 °C

Freezing to steady state (> 38 h)

Thawing to steady state at 3 °C

Steady state soil 3 °C

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