A vertical open-hole, concentric tube thermal well has the potential of being a more effective heat source for a ground-source heat pump than a closed-loop ground coupling with the same flow cross-sectional area because of the effect of the interchange of water with the aquifer. An analytical model describing this coupled thermohydraulic energy transfer in an aquifer surrounding a thermal well was developed. The differential equation for this coupled energy transfer by conduction and convection was written in cylindrical coordinates. The equation was simplified by the introduction of a "groundwater factor," which represents the ratio between convection and conduction, and solved numerically. Using the resulting data, an "equivalent thermal conductivity" can be found that accounts for the effect of induced groundwater flow. This equivalent thermal conductivity can be used in a conventional vertical ground heat exchanger performance computer program to calculate the required thermal well depth.

KEYWORDS: year 1995, ground water, heat flow, vertical, soil, heat pumps, wells, geothermal water, aquifers, geothermal energy, thermal conductivity, performance