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Numerical and finite element analysis of heat transfer in a closed loop geothermal system
2013-08, Hemmingway, Phil, Tolooiyan, Ali
Analysis of the thermal regime created by a geothermal borehole heat exchanger is performed using a closed form radial heat flow equation, a geothermal borehole heat exchanger design tool and a finite element model. Climatic, heat exchanger construction and building load data are entered into the heat exchanger design tool in order to create a theoretical model along with thermal parameters from a number of geological formations. Output data from the design tool model are used in conjunction with the closed form radial heat flow equation to calculate the predicted temperature with respect to time and distance from the heat exchanger for the modelled ground formations. The output data from the design tool is also used to create a number of finite element method models against which the predictions calculated using the closed form radial heat flow equation can be compared. A good correlation between the temperatures predicted by the finite element models and the closed form equation calculations is observed. However when used within its recommended limiting conditions, the closed form equation is shown to slightly underestimate the temperature of the ground when compared to the finite element model predictions. The limiting conditions associated with the closed form equation are discussed in the context of the output from the finite element method models.
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A preliminary study of the effect of groundwater flow on the thermal front created by borehole heat exchangers
2014-12, Tolooiyan, Ali, Hemmingway, Phil
This paper presents an analysis performed using a coupled TEMP/W-SEEP/W finite element model to consider both the conducive and convective effects of groundwater flow on the thermal regime created by a ground source energy system. The change in the development of the sub-surface thermal regime created by ground source energy borehole heat exchangers caused by a groundwater flow across a site, relative to a scenario where groundwater flow does not exist is examined. Analysis is performed using finite element formulations of both single borehole and multi borehole systems. The results of this work show that even a modest groundwater flow across a site can lead to a significant change in the development of the sub-surface thermal regime. It also shows that groundwater flow can result in implications for: proposed developments incorporating ground source energy systems; nearby existing ground source energy systems; potential future nearby ground source energy systems and the use of established software packages currently used for the design of ground source energy systems in the industry.