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Research Papers

Effects of Groundwater Flow on a Ground Source Heat Pump System

[+] Author and Article Information
Ayako Funabiki

Department of Mechanical Engineering,
College of Engineering,
Nihon University,
1 Nakagawara, Tokusada, Tamura-machi,
Koriyama 963-8642, Japan
e-mail: bickey@mech.ce.nihon-u.ac.jp

Masahito Oguma

Department of Mechanical Engineering,
College of Engineering,
Nihon University,
1 Nakagawara, Tokusada, Tamura-machi,
Koriyama 963-8642, Japan
e-mail: oguma@mech.ce.nihon-u.ac.jp

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received June 8, 2016; final manuscript received November 4, 2016; published online February 23, 2017. Assoc. Editor: Amir Jokar.

J. Thermal Sci. Eng. Appl 9(2), 021008 (Feb 23, 2017) (7 pages) Paper No: TSEA-16-1165; doi: 10.1115/1.4035502 History: Received June 08, 2016; Revised November 04, 2016

Heat advection by groundwater flow is known to improve the performance of ground heat exchangers (GHEs), but the effect of groundwater advection on performance is not yet fully understood. This numerical study examined how parameters related to groundwater flow, such as aquifer thickness, porosity, lithology, and groundwater flow velocity, affected the performance of a borehole GHE. Under a thin-aquifer condition (10 m, or 10% of the entire GHE length in this study), groundwater flow velocity had the greatest effect on heat flux. At a groundwater flow velocity of at least 10−4 m/s through a low-porosity aquifer filled with granite gravel with high thermal conductivity, the heat flux of a GHE was as much as 60% higher than that of a GHE in a setting without an aquifer. If the aquifer was as thick as 50 m, the high thermal conductivity of granite gravel doubled the heat flux of the GHE at a groundwater flow velocity of at least 10−5 m/s. Thus, not only groundwater flow velocity but also aquifer thickness and thermal conductivity were important factors. However, groundwater seldom flows at such high velocities, and porosity, gravel size and composition, and aquifer thickness vary regionally. Thus, in the design of ground source heat pump systems, it is not appropriate to assume a large groundwater effect.

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References

Figures

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Fig. 1

Schematic diagram of a GHE showing simulation parameters

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Fig. 2

Diagram showing grid structure of numerical simulation. The thick black line represents the GHE.

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Fig. 3

Diagram showing details of grid structure and groundwater flow parameters of the aquifer simulation

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Fig. 4

Heat flux values over time for different groundwater flow velocities

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Fig. 5

Heat flux values over time for different aquifer thicknesses

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Fig. 6

Heat flux profiles of a GHE with a water-filled aquifer after continuous operation for 50, 150, and 250 h

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Fig. 7

Heat flux profiles of a GHE with an aquifer filled with granite gravel after continuous operation for 50, 150, and 250 h

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Fig. 8

Heat flux values over time for different levels of aquifer porosity and lithology

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Fig. 9

Heat flux values over time for different groundwater flow velocities

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Fig. 10

Heat flux values over time for soils and gravels with different thermal properties

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Fig. 11

Heat flux values over time for soils with different thermal properties and different groundwater flow velocities

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Fig. 12

Heat flux values over time for dry sand and granite gravel and different groundwater flow velocities

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