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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