Standing column wells—Modeling the potential for applications in geothermal heating and cooling

Abstract

Standing column wells (SCWs) have the potential to deliver much higher rates of heat transfer to geothermal heating and cooling systems in buildings via heat pumps than can conventional vertical borehole heat exchange arrays. The development of a numerical model for clusters of standing column wells is described in this article. The model is three-dimensional, dynamic, and solves the governing equations using a finite-volume discretization scheme with a fully implicit algorithm. The slower-acting field equations are solved using a wider time interval than that used for the faster-acting well equations, and the two sets of equations are coupled through the field equation source terms. A groundwater bleed feature is incorporated. The model has been verified thermally and hydraulically using existing field data. Two test cases have been applied to reveal the advantages of using SCWs in U.K. conditions, competing with the conventional closed-loop system of vertical borehole heat exchangers. Results of the applications suggest that SCWs can deliver substantially higher rates of heat transfer than conventional closed loop borehole heat exchanger arrays, especially when groundwater bleed is operational. With appropriate earth conditions in the United Kingdom, SCWs can deliver space heating and direct cooling, for example, chilled beam or chilled ceiling, successfully to offer a substantial saving on carbon emissions. Another important practical consequence of this is that far less geotechnical drilling is needed when using standing column wells than is the case with closed-loop arrays.

Acknowledgments

Bobo M. Ng, Student Member ASHRAE, is PhD student. Chris P. Underwood, PhD, Member ASHRAE, is Professor. Sara L. Walker, PhD, is Principal Lecturer.