Field-based and predictive assessment of effective borehole thermal resistance in standing column wells
Standing column wells (SCWs) are ground heat exchangers that operate by recirculating groundwater in a deep uncased borehole and by bleeding a fraction of the water to stimulate advection during peak periods. While the high efficiency of SCWs is well recognized, the methodology to characterize their effective borehole thermal resistance remains poorly documented. To address this gap, an analysis was performed using data from 80-h thermal response tests conducted on eight SCWs across the St. Lawrence Lowlands in Canada. The nobleed phase of each test was analysed using line-source theory, and effective borehole thermal resistance values were inferred under uncertainty in a Bayesian framework. Results show that the inferred resistance range (0.005 to 0.025 m·°C/W) is markedly lower than that typically observed in conventional closed-loop boreholes, highlighting the thermal performance of SCWs. The comparison with predictions from the only existing theoretical formulation yielded a similar range (0.004 to 0.029 m·°C/W), with predicted values allowing to reproduce the no-bleed behaviour of SCWs with a mean relative error below 1% in seven out of eight wells. These findings provide the first integrated field-based and predictive assessment of effective borehole thermal resistance in SCWs. They demonstrate that precise estimation of this parameter can reliably reproduce SCW thermal behaviour during conduction-dominant operation and highlight its potential to support computationally efficient design tools.