Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan

 
 
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
energies
Article
Assessment of the Installation Potential of a Ground
Source Heat Pump System Based on the Groundwater
Condition in the Aizu Basin, Japan
Gaurav Shrestha 1, *, Youhei Uchida 1 , Takeshi Ishihara 1 , Shohei Kaneko 2 and
Satoru Kuronuma 3
 1   Renewable Energy Research Center, Fukushima Renewable Energy Institute, AIST, 2-2-9 Machiikedai,
     Koriyama 963-0298, Japan; uchida-y@aist.go.jp (Y.U.); t84-ishihara@aist.go.jp (T.I.)
 2   Graduate School of Symbiotic Systems Science and Technology, Fukushima University, Kanayagawa 1,
     Fukushima 960-1296, Japan; s1671002@ipc.fukushima-u.ac.jp
 3   Japan Groundwater Development Pvt. Ltd., Matsubara 777, Yamagata 990-2313, Japan; s-kuronuma@jgd.jp
 *   Correspondence: shrestha-g@aist.co.jp; Tel.: +81-29-861-2328
                                                                                                
 Received: 2 April 2018; Accepted: 27 April 2018; Published: 7 May 2018                         


 Abstract: Assessment of suitable locations for a ground source heat pump (GSHP) system based on
 the groundwater condition of study area is important for its sustainable development. Installation
 potential of a GSHP system was evaluated for the Aizu Basin, Japan. Firstly, suitability assessment
 was done for a conventional closed-loop system by preparing a distribution map of heat exchange
 rates for space heating. Heat exchange rates were higher at the northern and southern areas and
 lower at the central area, indicating that the northern and southern areas are appropriate for the
 conventional system. A different type of GSHP system using an artesian well was proposed at the
 central area because groundwater is flowing in an upward direction and using its heat energy can
 increase heat exchange rates. Demonstration of this system using an artesian well for space heating
 resulted in higher heat exchange rates compared to the conventional system. A GSHP system using
 an artesian well is suitable at the central area, and the conventional one is suitable at the northern
 and southern areas. Assessment of the installation potential of different types of GSHP system in the
 same Aizu Basin based on its groundwater condition is unique to this study. It can assist in selecting
 suitable locations for GSHP system installation and to promote its growth in Japan.

 Keywords: ground source heat pump system; installation potential; groundwater; heat exchange
 rate; artesian well



1. Introduction
      The ground source heat pump (GSHP) system is a competent and capable system for energy
and environment conservation. Low-enthalpy geothermal energy is used by this system for air
conditioning, heating, and so forth [1,2]. Growth of this system is increasing in Japan [3], but it is
still behind the expected goals as compared to Europe and America. The major reason for the slow
development is the higher capital cost resulting from a bigger design of the system than is needed.
Determination of suitable places to construct GSHP systems based on the groundwater condition of
the target region is essential for the best-suited design and sustainable growth of the system in Japan.
      Temperature structure under the ground is perturbed by groundwater flow due to its advection
effect, by which heat is transported with the flow [4–7]. Due to this, the groundwater condition of
the region strongly influences the heat exchange efficiency and performance of GSHP systems [8–12].
In the context of Japan, a large percentage of the population lives in urban areas, which are situated
on a Quaternary system. This Quaternary system acts as the main aquifers where groundwater flow


Energies 2018, 11, 1178; doi:10.3390/en11051178                            www.mdpi.com/journal/energies
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                              2 of 14



occurs [13]. Therefore, if the advantage of this groundwater could be effectively taken, the heat
exchange rate of a GSHP system can be increased efficiently.
      Some researches had evaluated the installation potential of a GSHP system in different areas
of Japan. Previous studies [1,14–17] had assessed the installation potential of a GSHP system in
plain and basin scales of Japan. In these studies, suitability maps were prepared that illustrate
appropriate places for the construction of a GSHP system, based on groundwater flow and heat
transport analysis. Fujii et al. [1] and Yoshioka et al. [15] calculated heat exchange rates at different
locations and mentioned their importance for suitable places and appropriate design of the system.
Uchida et al. [14] integrated the results of numerical analysis and hydrogeological field data to
prepare suitability maps for GSHP systems using the geographic information system (GIS). Shrestha
et al. [16] prepared the distribution map of effective thermal conductivity based on the results of
groundwater flow analysis and field data obtained from thermal response tests. Shrestha et al. [17]
evaluated the economic efficiency of GSHP systems by preparing the distribution map of the coefficient
of performance (COP) in addition to the distribution map of heat exchange rates. From the COP,
the electricity consumption of the system and its operational cost can be predicted, which can be useful
to select the suitable locations and optimum design of the system.
      These abovementioned studies to assess the installation potential at the regional scale are still
limited in Japan. On the basis of the abovementioned studies, suitable locations for GSHP system
installation can be evaluated. However, in these studies, only a conventional closed-loop system was
considered in their analyses. At the locations which are less suitable for this conventional system,
alternative types of systems that can be installed at those less suitable areas were not proposed at all.
In the current scenario, studies concerning the conventional system only will not lead to the growth
of the GSHP system as a whole. Evaluation of the installation potential of the GSHP system for both
suitable as well as less suitable locations is very crucial to enhance its sustainable use, as well as to
promote its further development in Japan. This kind of work has not been done until now. As already
mentioned, major Japanese cities are situated on alluvial plains and basins, with actively flowing
groundwater. Hence, the groundwater condition should be taken into consideration in order to assess
the installation potential of the system more accurately in the case of Japan. This study’s main objective
is to evaluate the installation potential of not only the conventional system, but also an alternative type
of system based on the groundwater condition of the target area.
      In this study, the installation potential of a GSHP system in the Aizu Basin was evaluated based on
the regional groundwater condition. Groundwater condition and underground temperature structure
of the Aizu Basin was analyzed by using a groundwater flow and heat transport model and a field
survey. Firstly, the assessment was done for the conventional closed-loop system by preparing a
distribution map of heat exchange rates for space heating. This map was prepared by using the results
of the heat exchange simulations conducted with ground heat exchanger (GHE) models constructed
at several locations within the Aizu Basin. The northern and southern areas were found to be more
appropriate for the conventional system with higher heat exchange rates. Then, at the less suitable
central area with lower heat exchange rates, a different type of GSHP system using an artesian (flowing)
well developed by Shrestha et al. [18] was proposed. It is because at these locations, groundwater
upflow is occurring, and utilizing its heat can enhance the system’s heat exchange performance.
Demonstration of this system using an artesian well for space heating resulted in higher heat exchange
rates compared to the conventional system at the central area. This kind of suitability assessment
and comparison of heat exchange performance of different types of GSHP systems in the same region
based on its groundwater condition is unique to this study. Additionally, this study can be effective
to select appropriate areas for the suitable types of GSHP systems, as well as to update the present
development trend of GSHP systems in the whole of Japan.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                                             3 of 14



2. Study Area
      The study area is the Aizu Basin, which is based in Fukushima Prefecture, Japan (Figure 1).
Its area  is about
Energies 2018, 11, x FOR  km2REVIEW
                      324PEER  , with the length of 30 km (N–S) and the width of 12 km (E–W). Elevation            of
                                                                                                              3 of 14
the basin varies from 170 m to 320 m. The Aizu Basin is surrounded by uplands composed of Upper
Neogene to   toMiddle
                  MiddlePleistocene
                            Pleistocene  sediments,
                                      sediments, withwith    elevation
                                                        elevation        varying
                                                                   varying         from
                                                                            from 300  m to300
                                                                                            400m m,to
                                                                                                    and400 m, and
                                                                                                         mountains
mountains
composed of    composed
                  Cretaceousof and
                               Cretaceous   and Middle
                                    Middle Miocene        Miocene
                                                      rocks,        rocks, with
                                                             with elevation      elevation
                                                                              varying        varying
                                                                                      from 1000   m tofrom
                                                                                                        20001000   m
                                                                                                             m [19].
to
This2000
      basinm is [19]. This by
                  formed    basin  is formedsediments
                               Quaternary     by Quaternary
                                                         carriedsediments
                                                                  by the Agacarried   by the
                                                                               River and       Aga River flowing
                                                                                           its tributaries  and its
tributaries
through the    flowing
                  basin. through  the basin.system
                          The Quaternary     The Quaternary
                                                     is composedsystem  is composed
                                                                    of sand            of sand
                                                                              and gravel,       andact
                                                                                            which    gravel, which
                                                                                                        as aquifers
act as aquifers
within   the basin. within the basin.




                                         Figure 1. Location of the Aizu Basin.

3.
3. Regional
   Regional Scale
            Scale 3D
                  3D Analysis
                     Analysis Model
                              Model
       Analysis
       Analysis ofof groundwater
                     groundwater flowflow and
                                            and heat
                                                  heat transport
                                                       transport must
                                                                  must toto be
                                                                            be done
                                                                                done for
                                                                                       for assessing
                                                                                             assessing the
                                                                                                         the installation
                                                                                                              installation
potential   of  a GSHP    system.  For  this purpose,   an  analysis  model   (Figure
potential of a GSHP system. For this purpose, an analysis model (Figure 2) developed by 2) developed      by  Shrestha   et
al.  [18] was   used  in this  paper.  The   finite element   program    FEFLOW      [20]  was
Shrestha et al. [18] was used in this paper. The finite element program FEFLOW [20] was used to   used  to  develop    this
analysis
develop model.       A brief
           this analysis      description
                           model.  A briefofdescription
                                               the analysisofmodel   is presented
                                                              the analysis  model below.
                                                                                     is presented below.
       Layers   1 to 33 are  taken  as the  aquifer  system,   and layers   34
       Layers 1 to 33 are taken as the aquifer system, and layers 34 to 39 are to  39 are   regarded
                                                                                         regarded     asas
                                                                                                         thethe bed
                                                                                                              bed     rock
                                                                                                                   rock  of
of  the Aizu    Basin.  Horizontal   mesh   of  the model   was  refined   along  the  rivers   and
the Aizu Basin. Horizontal mesh of the model was refined along the rivers and the major area of the   the  major  area   of
the
basin,basin,  and vertical
        and vertical   mesh mesh     was refined
                              was refined            at thelayers
                                             at the upper    uppercompared
                                                                     layers compared
                                                                               to the bottomto the   bottom
                                                                                                 layers        layers for
                                                                                                         for accuracy    in
accuracy    in the computations.     On  the  basis of past geological  borehole    recordings,     10
the computations. On the basis of past geological borehole recordings, 10 hydrogeological facies were  hydrogeological
facies   wereTable
classified.     classified.
                     1 shows Table
                               these1 hydrogeological
                                      shows these hydrogeological         faciesparameters
                                                          facies and physical     and physical       parameters
                                                                                                 of the             of the
                                                                                                        analysis model.
analysis   model.    As  groundwater     aquifers   are mainly   composed     of gravel    and   sand,
As groundwater aquifers are mainly composed of gravel and sand, their hydraulic conductivities were     their  hydraulic
conductivities
set in detail with were
                      theset in detail
                           model       withVolumetric
                                   depth.     the model depth.    Volumetric
                                                           heat capacity        heat
                                                                          of 2.52     capacity
                                                                                    MJ/m     3 /K of 2.52
                                                                                                   was     MJ/m3/K
                                                                                                        assigned    towas
                                                                                                                        the
assigned    to the model layers.
model layers.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                                                                  4 of 14
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       Figure2.2.Analysis
      Figure     Analysismodel
                          modelof ofthe
                                      theAizu
                                          AizuBasin.
                                               Basin. Reprinted
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                                                                                                             Aizu
      Basin,
       Basin,Japan,
              Japan,Shrestha
                     Shresthaetetal.,
                                  al.,2017).
                                       2017).

                                             Table1.1.Parameters
                                             Table     Parametersofofanalysis
                                                                      analysismodel.
                                                                              model.
                                           Hydraulic Conductivity (m/day)                                                      Thermal
  Hydrogeological
  Hydrogeological                          Hydraulic Conductivity (m/day)                                               Thermal Conductivity
      Facies
                         Layers 1       Layers 6       Layers 11       Layers 16     Layers 21        Porosity
                                                                                                     Porosity (-) (-)       Conductivity
                                                                                                                             (W/m/K)
        Facies    Layers 1 to 5 Layers 6 to 10  Layers 11 to 15    Layers 16 to 20 Layers 21 to 39
                             to 5           to 10            to 15        to 20           to 39                                (W/m/K)
     Top Soil        0.5              0.5               0.5              0.5               0.5          0.2                     1.4
        Top Soil
       Clay       1 × 10−4
                           0.5     1 × 10−4
                                            0.5      1 × 10−4
                                                             0.5             0.5
                                                                      1 × 10−4
                                                                                            0.5
                                                                                       1 × 10−4         0.450.2                 1.31.4
          Clay
        Silt        0.01 1 × 10 −4   0.01 1 × 10−4     0.011 × 10−4       1 × 10−4
                                                                        0.01             10.01
                                                                                            × 10−4       0.40.45                1.41.3
       SandSilt      8.0 0.01         4.0 0.01          1.6 0.01         0.80.01           0.4
                                                                                            0.01        0.350.4                 1.51.4
      Gravel        10.0              5.0               2.0              1.0              0.5           0.25                    1.6
          Sand
  Volcanoclastic           8.0              4.0              1.6              0.8          0.4             0.35                    1.5
                     1.0              1.0              1.0              1.0               1.0            0.2                    1.0
    material
         Gravel            10.0             5.0              2.0              1.0          0.5             0.25                    1.6
      Loam          0.02             0.02              0.02             0.02             0.02            0.4                    0.9
   Volcanoclastic
       Peat         0.01 1.0         0.01 1.0          0.01 1.0         0.011.0          0.01            0.50.2                 0.71.0
                                                                                           1.0
       material
      Others         0.5              0.5               0.5              0.5              0.5            0.2                    1.2
       Rock
         Loam     1 × 10−60.02     1 × 10−60.02      1 × 10−0.02
                                                            6                −6
                                                                      1 × 100.02           10−6
                                                                                       1 × 0.02         0.150.4                 2.50.9

      Reprinted
         Peat     by permission
                              0.01 from Springer
                                              0.01 Customer    Service Centre
                                                            0.01             0.01GmbH: Springer
                                                                                             0.01 HYDROGEOLOGY
                                                                                                           0.5        JOURNAL0.7
      (Performance
        Others        evaluation
                              0.5 of a ground-source
                                              0.5       heat0.5
                                                              pump system0.5   utilizing a flowing
                                                                                             0.5   well and0.2
                                                                                                            estimation of suitable
                                                                                                                             1.2
      areas for its installation
         Rock               1 × 10in
                                   −6 Aizu Basin, Japan, Shrestha
                                            1 × 10−6      1 × 10−6 et al., 12017).
                                                                             × 10−6       1 × 10−6         0.15              2.5
    Reprinted by permission from Springer Customer Service Centre GmbH: Springer
Boundary Conditions and Validation of Analysis Model
    HYDROGEOLOGY JOURNAL (Performance evaluation of a ground-source heat pump system
    Using  theaabove
    utilizing   flowinganalysis model,
                          well and      computation
                                   estimation         wasareas
                                              of suitable donefor
                                                               to its
                                                                  elucidate   the groundwater
                                                                      installation in Aizu Basin,system
                                                                                                  Japan, and
underground   temperature
    Shrestha et al., 2017). structure. To analyze the groundwater, surroundings of the model were
affixed with groundwater levels and rivers with elevations. The model’s bottom and vertical sides were
 Boundaryas
assumed     Conditions and Validation
              impervious.  To analyzeofthe
                                         Analysis Model temperature regime, the top of the model was
                                           underground
set with temperature based on the atmospheric temperature of the Aizu Basin, considering variation
      Using the above analysis model, computation was done to elucidate the groundwater system
in elevation, and the bottom was fixed with temperature calculated by using vertical temperature
 and underground◦ temperature structure. To analyze       the groundwater, surroundings of the model
gradients of 0.036 C/m for layers 1 to 33 and 0.060 ◦ C/m for layers 34 to 39.
 were affixed with groundwater levels and rivers with elevations. The model’s bottom and vertical
 sidesThe
       wereanalysis model had been validated by comparing the calculated results of groundwater levels
             assumed as impervious. To analyze the underground temperature regime, the top of the
and vertical distribution of underground temperature with their corresponding measured field data of
 model was set with temperature based on the atmospheric temperature of the Aizu Basin,
the existing wells in the basin [18]. Figures 3 and 4 show the verification of calculated hydraulic heads
 considering variation in elevation, and the bottom was fixed with temperature calculated by using
 vertical temperature gradients of 0.036 °C/m for layers 1 to 33 and 0.060 °C/m for layers 34 to 39.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018,
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            2018,  x FOR  PEER
                       x FOR   REVIEW
                             PEER REVIEW                                                                                    5 of5 14
                                                                                                                                  of 14

      The  analysis
         The         model
              analysis  model had  been
                                 had     validated
                                      been  validatedbybycomparing
                                                            comparing  thethe
                                                                            calculated
                                                                               calculatedresults  of of
                                                                                            results  groundwater
                                                                                                        groundwater
  Energies 2018, 11, 1178                                                                                          5 of 14
levels  and
   levels   vertical
          and        distribution
               vertical            of of
                        distribution  underground
                                         underground  temperature
                                                        temperature  with  their
                                                                        with     corresponding
                                                                              their corresponding  measured
                                                                                                      measured  field
                                                                                                                    field
data   of the  existing  wells  in the  basin  [18]. Figures   3 and    4 show    the  verification
   data of the existing wells in the basin [18]. Figures 3 and 4 show the verification of calculated of  calculated
hydraulic
   hydraulicheads
   and underground
               headsandandunderground
                        temperature
                            underground  temperature
                                       with temperature with
                                            their measured withtheir
                                                               data. measured
                                                                     More
                                                                  their            data.
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                                                                 the previous work
                                                                              et workbybyShrestha
                                                                                 al. [18].         et al.
                                                                                            Shrestha      [18].
                                                                                                      et al. [18].




     Figure  3. Comparison
        Figure  3. Comparison   of calculated      hydraulic heads   with measured    values.  Reprinted      by permission
        Figure 3.  Comparison of   of calculated
                                       calculated hydraulic
                                                      hydraulic heads
                                                                 heads with
                                                                        with measured    values.
                                                                             measured values.     Reprinted
                                                                                                  Reprinted by  by permission
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                                                                                                   JOURNAL (Performance
     (Performance
        (Performance  evaluation     of   a   ground-source      heat  pump    system   utilizing   a
        evaluation of a ground-source heat pump system utilizing a flowing well and estimation ofwell
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                                                                                                        a   flowing well andand
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                                                                                 Japan,
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         Figure
     Figure      4. Comparison
              4. Comparison        of calculated
                               of calculated      underground
                                              underground            temperature
                                                               temperature          distribution
                                                                              distribution  with   with measured
                                                                                                  measured          values.
                                                                                                              values. (a)(a)
         Figure  4. Comparison    of calculated  underground       temperature   distribution  with  measured   values.
         (a) Comparison
     Comparison      for   for
                         Well  Well
                               P-03; P-03;
                                      (b)  (b) comparison
                                          comparison     for   for
                                                              well  well P-12.
                                                                     P-12.     Reprinted
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         Comparison for Well P-03; (b) comparison for well P-12. Reprinted by permission from Springer
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         of a ground-source heat pump system utilizing a flowing well and estimation of suitable areas for its
     of aofground-source
            a ground-source heat pump
                               heat pump system  utilizing
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                                                                                                   of suitable    forfor
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         installation in Aizu Basin, Japan, Shrestha et al., 2017).
     installation  in Aizu
         installation       Basin,
                      in Aizu      Japan,
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                                       Japan, Shresthaet al., 2017).
                                                         et al., 2017).

  4. Ground Heat Exchanger Model
      In order to determine suitable areas for the construction of a GSHP system, a suitability map
  showing a distribution of heat exchange rates is considered to be useful. Assuming a conventional
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies2018,
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                11,x xFOR
                       FORPEER
                           PEERREVIEW
                                REVIEW                                                                           6 6ofof1414


4.4.Ground
     GroundHeat
            HeatExchanger
                 ExchangerModel
Energies 2018, 11, 1178
                          Model
                                                                                                                 6 of 14
       InInorder
            ordertotodetermine
                       determinesuitable
                                    suitableareas
                                               areasfor
                                                      forthe
                                                          theconstruction
                                                               constructionofofaaGSHP
                                                                                    GSHPsystem,
                                                                                           system,aasuitability
                                                                                                       suitabilitymapmap
  showingaadistribution
showing          distributionofofheat
                                   heatexchange
                                        exchangeratesratesisisconsidered
                                                               consideredtotobebeuseful.
                                                                                   useful.Assuming
                                                                                           Assumingaaconventional
                                                                                                         conventional
closed-loop
  closed-loop    system,
                  system,   identical ground
                           identical   groundheat  heatexchanger
                                                         exchanger    (GHE)
                                                                   (GHE)       models
                                                                            models       (Figure
                                                                                     (Figure 5) of 5) of dimensions
                                                                                                   dimensions     20mm××
closed-loop system, identical ground heat exchanger (GHE) models (Figure 5) of dimensions 20
2020mm××20  120mm × 120
                     were mconstructed
                             were constructed
                                          at  20   at 20 locations
                                                  locations   (Figure(Figure
                                                                      6) to    6) to compute
                                                                             compute    heat    heat exchange
                                                                                             exchange    rates  at rates
                                                                                                                    these
20 m × 120 m were constructed at 20 locations (Figure 6) to compute heat exchange rates at these
atlocations.
    these locations.    These
               Theselocations  locations
                       locationsare       are
                                  arereferred   referred  to
                                      referredtotohereafter   hereafter
                                                    hereafterasas“GHE   as  “GHE
                                                                   “GHElocations”. locations”.
                                                                           locations”.AsAsthe   As
                                                                                           theAizu  the Aizu
                                                                                                AizuBasin      Basin  is
                                                                                                      Basinisissituated
                                                                                                                situated
locations. These
situated    in a cold-weather    region  of  Japan,  computations     were   done  for space heating   purposes.
ininaacold-weather
        cold-weatherregion
                         regionofofJapan,
                                    Japan,computations
                                            computationswere  weredone
                                                                    donefor
                                                                          forspace
                                                                              spaceheating
                                                                                      heatingpurposes.
                                                                                              purposes.




      Figure
        Figure5.  Ground heat exchanger (GHE) model. (a) Three-dimensional model; (b) cross-sectional view
      Figure  5.5.Ground
                   Groundheat
                          heatexchanger
                               exchanger(GHE)
                                         (GHE)model.
                                               model.(a)
                                                      (a)Three-dimensional
                                                          Three-dimensionalmodel;
                                                                            model;(b)
                                                                                   (b)cross-sectional
                                                                                       cross-sectionalview
                                                                                                       view
      atatA–A’.
           A–A’.
      at A–A’.




                               Figure6.6.Locations
                              Figure      Locationsofofground
                                                        groundheat
                                                               heatexchanger
                                                                    exchangermodels.
                                                                              models.
                              Figure 6. Locations of ground heat exchanger models.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                                         7 of 14
Energies 2018, 11, x FOR PEER REVIEW                                                                            7 of 14


      GHE models
      GHE   modelswerewereconstructed
                             constructed    using
                                         using     the finite
                                               the finite elementelement
                                                                    programprogram
                                                                              FEFLOW  FEFLOW       [20]. Parameters
                                                                                          [20]. Parameters   adopted
for the GHE
adopted       models
          for the GHEare   the same
                         models   are as
                                      thethose
                                           sameassigned
                                                 as thosefor  the analysis
                                                           assigned   for themodel   as shown
                                                                               analysis  modelinasTable  1. For
                                                                                                     shown       each
                                                                                                             in Table
GHE
1. Formodel,
       each GHEthe same
                   model, geological
                            the samedata     and hydrological
                                       geological                 and thermaland
                                                    data and hydrological       parameters     from the same
                                                                                    thermal parameters      fromGHE
                                                                                                                  the
locations
same   GHEinlocations
               the analysis
                        in themodel   were
                               analysis       assigned.
                                          model           Similarly,
                                                  were assigned.       initial and
                                                                    Similarly,       boundary
                                                                                initial           conditions
                                                                                        and boundary           of the
                                                                                                         conditions
of
GHE themodels
         GHE were
                modelsset were
                          basedset    based
                                   on the      on the groundwater
                                           groundwater     flow velocity, flow   velocity,
                                                                             hydraulic       hydraulic
                                                                                         head,           head, and
                                                                                                 and underground
temperature calculated
underground     temperaturefrom   the analysis
                               calculated   frommodel   at each model
                                                  the analysis    GHE location.
                                                                         at each GHE location.
      At the center
              center nodes
                      nodes ofof the
                                  theGHE
                                       GHEmodels,
                                              models,a aground
                                                           groundheatheatexchanger
                                                                           exchanger  of of 100-m
                                                                                         100-m       depth
                                                                                                  depth  was was
                                                                                                               set.set.
                                                                                                                    A
double
A  doubleU-tube
            U-tubeofofdiameter
                        diameter3434mm mmand andgrout
                                                  grout ofof silica
                                                             silica sand
                                                                    sand were considered. For groundwater
analysis, the models’ top and bottom were assumed as impervious   impervious without
                                                                                without anyany flow. Vertical faces
                with groundwater
were affixed with    groundwater levels to obtain the same flow velocities that were computed at the
                                                 underground temperature, results gained from the analysis
same points from the analysis model. For underground
model were assigned to all layers.

Distribution Map
Distribution Map of
                 of Heat
                    Heat Exchange
                         Exchange Rates
                                  Rates
     For
     For each
          each GHE
                GHE model
                     model atat the
                                the respective
                                    respective locations,     heat exchange
                                                  locations, heat   exchange simulations
                                                                                simulations were
                                                                                               were done
                                                                                                     done for
                                                                                                          for space
                                                                                                              space
heating.  The operating  scenario  was   set as 120  days  of space   heating  per year  from
heating. The operating scenario was set as 120 days of space heating per year from December to  December  to March,
with
March,24-h operation.
         with          The inlet
              24-h operation.    temperature
                               The               and flow
                                     inlet temperature       rate
                                                           and    of circulation
                                                                flow               fluid were
                                                                       rate of circulation      maintained
                                                                                            fluid            as 5 ◦ C
                                                                                                  were maintained
and5 20
as   °CL/min,
         and 20 respectively.  Water isWater
                 L/min, respectively.     taken as   a circulation
                                                 is taken           fluid. From
                                                            as a circulation      the From
                                                                               fluid. simulations,   heat exchange
                                                                                              the simulations,  heat
rates at GHE   locations  were  estimated.    On   the  basis of estimated    values,  a distribution
exchange rates at GHE locations were estimated. On the basis of estimated values, a distribution       map of map
                                                                                                                heat
exchange
of         rates (Figure
   heat exchange         7) in the7)Aizu
                   rates (Figure           Basin
                                      in the Aizuwas    prepared
                                                    Basin          using ArcGIS.
                                                           was prepared      using ArcGIS.




                                Figure 7. Distribution
                                Figure 7. Distribution map of heat
                                                       map of heat exchange
                                                                   exchange rates.
                                                                            rates.

     Heat exchange rates were found to be higher at the northern and southern areas of the basin,
     Heat exchange rates were found to be higher at the northern and southern areas of the
which are the upstream areas of rivers flowing from the north and south parts, respectively. Heat
basin, which are the upstream areas of rivers flowing from the north and south parts, respectively.
exchange rates at the central basin were lower compared to these areas. The distribution map of heat
Heat exchange rates at the central basin were lower compared to these areas. The distribution map
exchange rates (Figure 7) indicates that the northern and southern areas are more suitable for
of heat exchange rates (Figure 7) indicates that the northern and southern areas are more suitable for
installing conventional closed-loop GSHP systems than the central basin. This is because
installing conventional closed-loop GSHP systems than the central basin. This is because groundwater
groundwater flow velocities were found to be higher at these upstream northern and southern areas
and lower at the central area. Figure 8 shows the distribution map of groundwater flow velocity in
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                                             8 of 14



flow velocities were found to be higher at these upstream northern and southern areas and lower
Energies 2018, 11, x FOR PEER REVIEW                                                                                8 of 14
at the central area. Figure 8 shows the distribution map of groundwater flow velocity in the Aizu
basin,
the    resulting
     Aizu  basin, from   the analysis
                    resulting   from the model.   Groundwater
                                            analysis               flow velocities
                                                       model. Groundwater        flowarevelocities
                                                                                          higher at are
                                                                                                     the higher
                                                                                                          northern at and
                                                                                                                       the
southern   areas  because   of   higher   hydraulic    gradients   and  preferable   geology    at
northern and southern areas because of higher hydraulic gradients and preferable geology at these  these  areas.   When
the groundwater
areas.  When the flow      velocity is
                      groundwater         higher,
                                       flow        the apparent
                                              velocity    is higher,thermal   conductivity
                                                                      the apparent    thermal of conductivity
                                                                                                  the subsurface   of also
                                                                                                                       the
increases,  caused    by heat transfer    through    groundwater      advection   [16,21–24].   Higher
subsurface also increases, caused by heat transfer through groundwater advection [16,21–24]. Higher       flow  velocity
also assists
flow  velocityin retrieving
                 also assiststhein heat  energythe
                                    retrieving    at the
                                                      heatGHE,   which
                                                             energy      thereby
                                                                     at the  GHE,improves       heat exchange
                                                                                     which thereby      improves  rate
                                                                                                                     heatof
the systemrate
exchange     by of
                 maintaining
                    the system constant      subsurface
                                  by maintaining            temperature
                                                     constant   subsurfaceat temperature
                                                                             and around the      GHE.
                                                                                             at and      At the
                                                                                                     around    thecentral
                                                                                                                    GHE.
area, there  are clay  layers in   the underground       [25]. Presence  of these  clay  layers  and
At the central area, there are clay layers in the underground [25]. Presence of these clay layers and  small  hydraulic
gradients
small      at the central
       hydraulic            area
                    gradients    atare
                                    thethe  mainarea
                                        central    factors
                                                        are influencing   the low
                                                             the main factors       groundwater
                                                                                influencing          flowgroundwater
                                                                                               the low      velocities at
this area.
flow       Because
      velocities     of these
                  at this area.lower   groundwater
                                  Because               flow velocities,
                                            of these lower     groundwaterheatflow
                                                                               exchange    rates heat
                                                                                    velocities,  for the   conventional
                                                                                                        exchange    rates
closed-loop    system   were also    lower  at the central   area.
for the conventional closed-loop system were also lower at the central area.




                             Figure
                             Figure 8.
                                    8. Distribution
                                       Distribution map
                                                    map of
                                                        of groundwater
                                                           groundwater flow
                                                                       flow velocity.
                                                                            velocity.

5. GSHP System Using an Artesian Well
5. GSHP System Using an Artesian Well
     To use a GSHP system at the central area of the Aizu Basin, an alternative solution to the
     To use a GSHP system at the central area of the Aizu Basin, an alternative solution to the
conventional closed-loop system should be proposed. A different type of GSHP system is necessary
conventional closed-loop system should be proposed. A different type of GSHP system is necessary
that can perform better even at the central area, where the heat exchange rates for the conventional
that can perform better even at the central area, where the heat exchange rates for the conventional
closed-loop system are lower. As already mentioned above, the existence of distributed clay layers at
closed-loop system are lower. As already mentioned above, the existence of distributed clay layers
the central area acts as a confining layer, forming an artesian zone. Hence, areas located at the central
at the central area acts as a confining layer, forming an artesian zone. Hence, areas located at the
basin have higher hydraulic potential, and the artesian pressure makes groundwater flow in the
central basin have higher hydraulic potential, and the artesian pressure makes groundwater flow in
upward direction [25]. Also, from the field survey, it was known that existing artesian wells were
the upward direction [25]. Also, from the field survey, it was known that existing artesian wells were
distributed at the central area, as shown in Figure 9. If the groundwater of this central area can be
distributed at the central area, as shown in Figure 9. If the groundwater of this central area can be
effectively utilized, heat exchange rates of the system can be enhanced. As groundwater at this central
effectively utilized, heat exchange rates of the system can be enhanced. As groundwater at this central
area is flowing in the upward direction, the system using an artesian well is taken as the best possible
area is flowing in the upward direction, the system using an artesian well is taken as the best possible
option to increase heat exchange rates of the system.
option to increase heat exchange rates of the system.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                             9 of 14
Energies 2018, 11, x FOR PEER REVIEW                                                                9 of 14




                 Figure 9. Distribution of existing artesian wells and springs in the Aizu Basin.

      In this study, the GSHP system using an artesian well developed by Shrestha et al. [18] is taken
      In this study, the GSHP system using an artesian well developed by Shrestha et al. [18] is taken
into consideration as an alternative system that can be used at the central area. For demonstration
into consideration as an alternative system that can be used at the central area. For demonstration
purpose, this system was constructed at the central area (Figure 1). In this area, the heat exchange
purpose, this system was constructed at the central area (Figure 1). In this area, the heat exchange rates
rates for the conventional closed-loop system were found to be lower (Figure 7). The artesian well of
for the conventional closed-loop system were found to be lower (Figure 7). The artesian well of 100-m
100-m depth with double U-tubes and 10-kW heat pumps were used (Figure 10). More details about
depth with double U-tubes and 10-kW heat pumps were used (Figure 10). More details about this
this system can be referred to in the previous work by Shrestha et al. [18].
system can be referred to in the previous work by Shrestha et al. [18].
      Space heating operation was conducted with this system during the winter season from
      Space heating operation was conducted with this system during the winter season from December
December 2016 to March 2017. Figure 11 shows the temporal variation of the obtained heat exchange
2016 to March 2017. Figure 11 shows the temporal variation of the obtained heat exchange rate during
rate during its operational period. The average heat exchange rate was found to be 54.8 W/m, with a
its operational period. The average heat exchange rate was found to be 54.8 W/m, with a maximum
maximum value of 72.4 W/m and a minimum value of 34 W/m. These values are higher compared to
value of 72.4 W/m and a minimum value of 34 W/m. These values are higher compared to the
the heat exchange rates of the conventional closed-loop system at the central area of basin (Figure 7),
heat exchange rates of the conventional closed-loop system at the central area of basin (Figure 7),
which ranged from 28 W/m to 31 W/m.
which ranged from 28 W/m to 31 W/m.
      In this system, the source of heat for space heating is the groundwater of the artesian well itself,
      In this system, the source of heat for space heating is the groundwater of the artesian well
flowing in the upward direction. For the conservation of groundwater use and keeping the
itself, flowing in the upward direction. For the conservation of groundwater use and keeping the
temperature within the well constant, the upflow of groundwater was controlled by the electric valve
temperature within the well constant, the upflow of groundwater was controlled by the electric
[18]. Because of maintaining constant temperature, the heat exchange rate of this system was higher,
valve [18]. Because of maintaining constant temperature, the heat exchange rate of this system was
although the heat is continuously taken for space heating.
higher, although the heat is continuously taken for space heating.
      Specification of this system is briefly explained below, based on the previous work by Shrestha
      Specification of this system is briefly explained below, based on the previous work by
et al. [18]. During space heating operation, once the temperature within the well decreases to 10 °C,
Shrestha et al. [18]. During space heating operation, once the temperature within the well decreases to
the valve opens, substituting the groundwater within the well by new groundwater from the aquifer.
10 ◦ C, the valve opens, substituting the groundwater within the well by new groundwater from the
When the temperature increases to 12 °C (original      temperature of the well), the valve gets closed.
aquifer. When the temperature increases to 12 ◦ C (original temperature of the well), the valve gets
This process repeats, keeping the temperature constant within the well. In this way, the heat source
of space heating is continuously retained, and the performance of the system is well maintained.
Assessment of the Installation Potential of a Ground Source Heat Pump System Based on the Groundwater Condition in the Aizu Basin, Japan
Energies 2018, 11, 1178                                                                                                10 of 14



closed. This process repeats, keeping the temperature constant within the well. In this way, the heat
Energies
 Energies2018,
          2018,11,
                11,xxFOR
                      FORPEER
                          PEERREVIEW
                               REVIEW                                                           10
                                                                                                 10of
                                                                                                    of14
                                                                                                       14
source of space heating is continuously retained, and the performance of the system is well maintained.




      Figure
       Figure10.
      Figure   10.Ground
              10.  Groundsource
                  Ground    sourceheat
                            source  heatpump
                                    heat  pump(GSHP)
                                         pump      (GSHP)system
                                                  (GSHP)    systemusing
                                                           system   usingan
                                                                   using  anartesian
                                                                         an   artesianwell.
                                                                             artesian  well.Reprinted
                                                                                      well.   Reprintedby
                                                                                            Reprinted       bypermission
                                                                                                           by   permission
                                                                                                               permission
      from
      from   Springer
       fromSpringer
              Springer    Customer
                           Customer
                       Customer         Service
                                  Service  Centre Centre
                                         Service             GmbH:
                                                    Centre Springer
                                                    GmbH:              Springer
                                                                        Springer HYDROGEOLOGY
                                                              GmbH: HYDROGEOLOGY    HYDROGEOLOGY               JOURNAL
                                                                                                                JOURNAL
                                                                                             JOURNAL (Performance
      (Performance
      evaluation of a ground-source heat pump system utilizing a flowing well and estimation ofwell
       (Performance    evaluation
                        evaluation  of
                                     of aa  ground-source
                                             ground-source    heat
                                                               heat pump
                                                                     pump   system
                                                                             system  utilizing
                                                                                      utilizing   aa  flowing
                                                                                                       flowing   well and
                                                                                                                       and
                                                                                                                  suitable
      estimation
       estimation  of
                    ofsuitable
                       suitableareas
                                areasfor
                                      for its
                                           itsinstallation
                                               installationin
                                                            inAizu
                                                               Aizu Basin,
                                                                     Basin,Japan,
                                                                            Japan,
      areas for its installation in Aizu Basin, Japan, Shrestha et al., 2017).     Shrestha
                                                                                    Shrestha  et
                                                                                               etal.,
                                                                                                  al., 2017).
                                                                                                        2017).




        Figure
        Figure 11.
         Figure11. Variation
                11.Variation of
                   Variationof  heat
                              ofheat exchange
                                 heatexchange rates
                                      exchangerates of
                                               ratesof the
                                                     ofthe system
                                                            systemusing
                                                        thesystem  usingan
                                                                  using  anartesian
                                                                        an  artesianwell
                                                                           artesian wellfor
                                                                                    well  forspace
                                                                                         for  spaceheating.
                                                                                             space heating.
                                                                                                    heating.

AppropriateLocations
Appropriate Locationsfor
                      foraaGSHP
                           GSHPSystem
                                SystemUsing
                                      Usingan
                                            anArtesian
                                               ArtesianWell
                                                       Well
     Artesian
      Artesianwells
                wellsarearegenerally  formed
                            generallyformed
                                       formedbyby upflowing
                                               byupflowing      groundwater
                                                   upflowinggroundwater         driven
                                                                groundwaterdriven
                                                                                drivenby by artesian
                                                                                         byartesian   pressure
                                                                                            artesianpressure    [26].
                                                                                                      pressure[26].
Therefore,
Therefore,  groundwater
 Therefore, groundwater     discharge
              groundwater discharge    areas
                              discharge areasare suitable
                                          areas are        for
                                                 are suitable  the
                                                      suitable for construction
                                                                 for the          of the
                                                                      the construction   system
                                                                           construction ofof the  using
                                                                                              the system an artesian
                                                                                                   system using
                                                                                                           using anan
artesian
 artesian well.
           well. Figure
                  Figure 1212 shows
                               shows the
                                       the distribution
                                           distribution mapmap of of groundwater
                                                                      groundwater discharge
                                                                                      discharge areas
                                                                                                   areas which
                                                                                                          which are
                                                                                                                  are
computed
 computedfromfromthetheanalysis
                         analysismodel
                                  model(Figure
                                          (Figure2)2)[18].
                                                       [18].Computed
                                                             Computedgroundwater
                                                                           groundwaterdischarge
                                                                                          dischargeareas,
                                                                                                       areas,except
                                                                                                              except
along
 alongthe
        theriver,
            river, and
                    and existing
                         existingartesian
                                  artesian wells
                                            wells in
                                                   in the
                                                       thefield
                                                           fielddetermined
                                                                  determined from
                                                                                fromthethefield
                                                                                           field survey
                                                                                                  survey(Figure
                                                                                                          (Figure9) 9)
were
 weredistributed
       distributedat atthe
                        thecentral
                            centralarea.
                                    area.
Energies 2018, 11, 1178                                                                                            11 of 14



well. Figure 12 shows the distribution map of groundwater discharge areas which are computed from
the analysis model (Figure 2) [18]. Computed groundwater discharge areas, except along the river,
and  existing artesian wells in the field determined from the field survey (Figure 9) were distributed
Energies 2018, 11, x FOR PEER REVIEW
                                                                                                                    at
                                                                                                              11 of 14
the central area.
      Therefore,
      Therefore, the the system
                         system using
                                 using an
                                       an artesian
                                            artesian well
                                                     well is
                                                           is suitable
                                                               suitable for
                                                                        for installation
                                                                            installation at
                                                                                          at the
                                                                                             the central
                                                                                                 central area
                                                                                                         area where
                                                                                                              where
groundwater
groundwater is     is flowing
                      flowing in
                               in an
                                  an upward
                                      upward direction
                                                 direction andand its
                                                                   its velocity
                                                                       velocity is
                                                                                 is low.
                                                                                     low. On
                                                                                          On the
                                                                                               the other
                                                                                                   other hand,
                                                                                                          hand, the
                                                                                                                  the
conventional      closed-loop  system  is suitable  at the upstream     northern  and  southern   parts
conventional closed-loop system is suitable at the upstream northern and southern parts of the basin,   of the basin,
where
where groundwater
         groundwater flow flow velocity
                               velocity is
                                         is higher
                                            higher than
                                                    than at
                                                          at the
                                                              thecentral
                                                                  centralarea.
                                                                          area.




      Figure 12.
      Figure   12. Distribution
                   Distributionmap
                                 mapofofgroundwater
                                          groundwater    upflow
                                                      upflow     areas
                                                              areas    (white
                                                                    (white     areas).
                                                                           areas).      Reprinted
                                                                                   Reprinted      by permission
                                                                                             by permission  from
      from Springer
      Springer         Customer
                 Customer         Service
                             Service      Centre
                                     Centre   GmbH:GmbH:  Springer
                                                     Springer      HYDROGEOLOGY
                                                               HYDROGEOLOGY              JOURNAL
                                                                                      JOURNAL       (Assessment
                                                                                                 (Assessment   of
      of installation  potential of ground-source   heat pump   system  based  on  the groundwater   condition
      installation potential of ground-source heat pump system based on the groundwater condition in Aizu      in
      Aizu  Basin,  Japan, Shrestha  et al.,
      Basin, Japan, Shrestha et al., 2017).  2017).

6. Conclusions
6. Conclusions
      In this
      In  thisstudy,
                study,thethe installation
                           installation      potential
                                         potential  of aof  a GSHP
                                                         GSHP    systemsystem    was evaluated
                                                                          was evaluated      for thefor
                                                                                                     AizutheBasin,
                                                                                                              Aizulocated
                                                                                                                    Basin,
located
in Japan,inbased
               Japan,    based
                     on its       on its
                            regional        regional groundwater
                                       groundwater                       condition. Groundwater
                                                         condition. Groundwater          condition andcondition
                                                                                                           underground and
underground       temperature     structure    of the basin  was   analyzed    by   using  a  3D  analysis
temperature structure of the basin was analyzed by using a 3D analysis model and a field survey. Firstly,    model  and   a
field  survey.    Firstly,  suitability   assessment    was   done    for  a  conventional      closed-loop
suitability assessment was done for a conventional closed-loop system by preparing a distribution map          system   by
preparing
of            a distribution
   heat exchange                map of
                     rates for space      heat exchange
                                       heating.             rates foridentical
                                                  For this purpose,     space heating.     For this
                                                                                  GHE models      werepurpose,   identical
                                                                                                        constructed   at 20
GHE    models     were   constructed    at 20  locations  using   the finite  element
locations using the finite element program FEFLOW. A 100-m deep ground heat exchanger wasprogram     FEFLOW.     A 100-m
                                                                                                                     set at
deep
the    ground
    center       heat
             of the GHE exchanger
                           models, was     set at the
                                     consisting   of acenter
                                                       doubleofU-tube
                                                                 the GHEwithmodels,     consisting
                                                                               outer diameter        of mm.
                                                                                                  of 34 a double   U-tube
                                                                                                              To compute
withexchange
heat   outer diameter      of 34
                  rates, heat     mm. Tosimulations
                               exchange       compute heatwereexchange
                                                                conductedrates,     heat exchange
                                                                             with these   GHE models.  simulations   were
                                                                                                            Space heating
conducted     with   these  GHE    models.    Space  heating   operations    were    conducted
operations were conducted for 120 days per year from December to March. From the simulations,     for 120  days  per  year
fromexchange
heat   Decemberratesto March.   From the simulations,
                          were computed                     heat and
                                              at each location,  exchange     rates weremap
                                                                      the distribution     computed
                                                                                                 of heatatexchange
                                                                                                            each location,
                                                                                                                     rates
and   the  distribution    map   of heat   exchange    rates  was   prepared    using   ArcGIS.
was prepared using ArcGIS. Heat exchange rates were found to be higher at the northern and southernHeat   exchange   rates
were   found   to be  higher  at the  northern    and southern    areas  of the  basin,  which   are the
areas of the basin, which are the upstream areas of rivers flowing from the north and south parts of the  upstream   areas
of rivers
basin;     flowing
        while   at thefrom  the basin,
                        central north and
                                        heatsouth    partsrates
                                               exchange    of the  basin;
                                                                 were     while
                                                                       found    to at
                                                                                   bethe  central
                                                                                       lower.  Thebasin,   heat exchange
                                                                                                     distribution  map of
rates were found to be lower. The distribution map of heat exchange rates shows that the northern
and southern areas are more suitable for installing the conventional closed-loop GSHP systems than
the central area. Higher heat exchange rates are because of higher groundwater flow velocities at the
upstream northern and southern areas. Groundwater flow velocities are higher at these areas because
of higher hydraulic gradients and preferable geology. Higher flow velocity increases the apparent
Energies 2018, 11, 1178                                                                                 12 of 14



heat exchange rates shows that the northern and southern areas are more suitable for installing the
conventional closed-loop GSHP systems than the central area. Higher heat exchange rates are because
of higher groundwater flow velocities at the upstream northern and southern areas. Groundwater
flow velocities are higher at these areas because of higher hydraulic gradients and preferable geology.
Higher flow velocity increases the apparent thermal conductivity of the subsurface because of the
advection effect of groundwater flow, and ultimately increases heat exchange rates; while at the central
area, the presence of clay and a small hydraulic gradient cause the low groundwater flow velocities.
Due to this, heat exchange rates for the conventional closed-loop system are lower at the central area.
      For promoting the use of a GSHP system in the Aizu Basin, the development of a different type of
GSHP system other than the conventional system that can perform better even at the central area is
very essential. At the central area, although the flow velocity is low, groundwater is found to be flowing
in an upward direction. Also found from the field survey, artesian wells were distributed at the central
basin. Utilizing the heat energy of this upflowing groundwater can increase the heat exchange rate of
the system. Hence, in this study, the GSHP system using an artesian well is taken as the best possible
option that can produce higher heat exchange rates at the central area. For demonstration purpose,
this system was installed at the central area, where the heat exchange rates for the conventional
closed-loop system were found to be lower. The artesian well of 100-m depth was used with double
U-tubes and 10-kW heat pumps. Space heating operation was conducted with this system during
the winter season from December 2016 to March 2017. This system with an artesian well showed a
higher heat exchange rate with an average value of 54.8 W/m, which is higher than that estimated
for the conventional closed-loop system at the central area. It can be said that an artesian well can be
efficiently used to increase the heat exchange rate of a GSHP system.
      From this study, it can be said that the system using an artesian well is suitable for installation at
the central area with groundwater upflow. On the other hand, the conventional closed-loop system is
suitable at the upstream northern and southern parts of the basin, where groundwater flow velocity is
higher than in the central area. In this way, the suitability assessment and comparison of heat exchange
performance of different types of GSHP systems in the same region based on its groundwater condition
is the originality of this study, which had not been performed previously. It can be said that this study
and its results are significant to selecting appropriate areas for the accurate design of GSHP systems
and also for the widespread growth of the system in Japan.
      Regarding limitations of this study, all the specifications of the GSHP system using an artesian
well could not be adopted in the heat exchange simulations because of complications in the modelling
of ground heat exchangers and for accuracy in calculations. As a further study, heat exchange rates
will be computed for space cooling operations as well as for the both conventional closed-loop system
and the GSHP system using an artesian well. Furthermore, the results of this study will be compared
with those of different study areas in order to upgrade the methodology of the suitability assessment
based on inter-regional analysis.

Author Contributions: Gaurav Shrestha is the principal investigator of this work who prepared this manuscript.
Youhei Uchida advised on the groundwater flow system and subsurface temperature. Takeshi Ishihara contributed
on the hydrogeology. Shohei Kaneko contributed on the analysis of groundwater condition and its temperature
distribution. Satoru Kuronuma contributed on the GSHP system using an artesian well. All authors approved
the manuscript.
Acknowledgments: Authors would like to thank Springer Customer Service Centre GmbH for granting a license
to reuse the material in this manuscript. Authors also thank the reviewers of this manuscript for their valuable
comments. This study is partly supported by the Technology Support Program for Industrial Firms in Fukushima,
Miyagi, and Iwate Prefectures of Japan.
Conflicts of Interest: Authors declare no conflict of interest.
Energies 2018, 11, 1178                                                                                        13 of 14



Nomenclature
COP       Coefficient of performance
GHE       Ground heat exchanger
GSHP      Ground source heat pump
3D        Three-dimensional

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