Effects of depth and material property variations on the ground temperature response to heating by a deep vertical ground heat exchanger in purely conductive media

摘要

This paper explores the depth dependence of the ground temperature response to heating by a deep vertical borehole ground heat exchanger by comparing experimental results to various models of ground heat exchange. The results of this analysis show that the specific heat exchange rate per unit-depth of borehole can vary with depth, including within individual strata. This explained the experimental results which showed that the ground temperature response varied significantly with depth. The analysis also showed that the specific heat exchange rate can vary in time, in addition to depth, such that the total heat transfer rate (specific heat exchange rate integrated over the entire borehole) remains constant in time. This property of the refined model explained anomalous results in the lower portions of the depth which we show that other models could not explain. We believe this is a new area of research because models of transient ground heat exchanger output typically consider bulk effects resulting from load variation (e.g. Bernier, 2001; Deerman and Kavanaugh, 1991) or the short-term effects of thermal storage and transmission within the grout itself (e.g. Claesson and Eskilson, 1988). Perhaps future studies will find ways of using the stratification of ground heat exchanger output in an advantageous way. Alternately, consideration of these effects may improve the modelling of ground heat exchanger systems.