Content area
Full Text
Thermogeological assessment of open-loop well-doublet schemes: a review and synthesis of analytical approaches
David Banks
Abstract Use of well doublets for groundwater-sourced heating or cooling typically results in a thermal plume of cool or warm reinjected groundwater. Such a plume may be regarded either as a potential anthropogenic geothermal resource or as pollution, depending on downstream aquifer usage. A thermal plume may pose an external risk to downstream users and environmental receptors or an internal risk to the sustainability of the well doublet, due to the phenomenon of thermal feedback. A three-tier assessment of the risk of thermal feedback is proposed, based on: (1) consideration of well separation and yield; (2) analytical modelling of heat migration in a doublet to ascertain breakthrough time and post-breakthrough temperature evolution and (3) numerical modelling of complex scenarios.
Keywords Heat transport . Analytical solutions . Cooling . Well doublet . Groundwater ow
Introduction
The objective of this paper is to re-acquaint a new generation of hydrogeologists with the pioneering analyses of the performance of well-doublet ground source heat schemes by early researchers (Gringarten and Sauty 1975; Tsang et al. 1977) and to synthesise these into a tiered approach to thermogeological risk assessment of the sustainability of such schemes.
The ground (or groundwater) has been widely used as a heat source or sink for space heating and cooling for many decades. The ground source heat pump (GSHP) was patented by Heinrich Zoelly in 1912 (Ball et al. 1983; Spitler 2005; Kelley 2006). Even before the GSHP became widespread, groundwater from shallow conned aquifers below Shanghai, China, is reported to have been abstracted and used for cooling workshops and factories. This led to over-abstraction and serious ground subsidence until, in the 1960s, the authorities strictly limited shallow consumptive abstraction. Moreover, they commenced re-injecting cold surplus winter surface water into deeper aquifer horizons in an attempt to create a sustainable resource of groundwater coolth (Luxiang and Manfang 1984; Volker and Henry 1988). Groundwater was also a popular solution for space cooling in Brooklyn and Long Island, USA in the 1920s and 1930s: so popular, in fact, that there began to be fears that the large scale abstraction of groundwater would deplete the aquifer resource. Authorities then began to insist that the warmer...