thermal energy storage in borehole heat exchanger arrays · thermal energy storage in borehole heat...
TRANSCRIPT
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Thermal Energy Storage in Borehole Heat Exchanger Arrays
John S. McCartney, Ph.D., P.E. Associate Professor
University of California San DiegoSymposium on Energy Geotechnics, UPC Barcelona
June 2nd, 2015
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Acknowledgements
• Sponsor: NSF SEP Grant CMMI 1230237 • Collaborators:
– Ning Lu, Colorado School of Mines (geotech. eng.)– Shemin Ge, University of Colorado Boulder (hydrogeologist)– Kathleen Smits, Colorado School of Mines (env. science)– Adam Reed, University of Colorado Boulder (energy policy)
• Graduate Students:– Tugce Baser, UC San Diego– Nora Catolico, CU Boulder
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Presentation Overview
• Overview of Soil‐Borehole Thermal Energy Storage (SBTES) systems
• Simulation of Drake Landing Solar Community SBTES system using TOUGH2
• Design simulations of a small‐scale SBTES in Golden, CO using COMSOL
• Field data from small‐scale SBTES in Golden, CO• Simulations of the scalability of SBTES systems• Upcoming large‐scale SBTES system in San Diego, CA
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District Heating using Solar Thermal Energy
Challenge: Heat storage
4
Drake Landing, Canada
Braedstrup, Denmark
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Heat Storage Option: Geothermal Boreholes
5
Sheffield, UK
Drake Landing, Canada
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SBTES System Operation
6
Heat Injection Heat Extraction
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SBTES Systems within the Vadose Zone
7
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Operation of SBTES Systems
8
Overall study goals:1. Understand the role of heat
exchanger array geometry 2. Calibrate models using field-
scale data from existing and new SBTES sites
3. Evaluate coupled heat transfer and water flow processes in the vadose zone
4. Understand scalability of SBTES arrays
5. Evaluate ways to improve the efficiency of heat extraction
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Drake Landing Solar Community (DLSC)
Drake Landing Solar Community (DLSC) Okotoks, Alberta,
Canada
35mx35mx35m SBTES used to provide 95% of the heat to 52 homes
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DLSC SBTES Numerical Model Domain
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DLSC Numerical Model (TOUGH2)
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Boundary Conditions and Calibrated Parameters
12
Parameter Value Unit
Soil Particle Density ƚ 2480 kg/m3
Soil Permeability 1.5x10‐14 m2
Soil Thermal Conductivity ƚ 2.03 w/m°C
Soil Porosity ƚ 0.50 m3/m3
Soil Heat Capacity ƚ 935.80 J/kg°C
Fluid Density 1000 kg/m3
Fluid Heat Capacity 4183 J/kg°CU‐tube Thermal Conductivity 0.51 w/m°C
Insulation Layer Thermal Conductivity ƚ 0.23 w/m°C
U‐tube Radius 0.055 mvan Genuchten m 0.5van Genuchten a 0.01 kPa‐1
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DLSC Simulated Seasonal Ground Temperatures
13
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DLSC Simulation vs. Measured Values
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DLSC Simulation vs. Measured Values
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DLSC Simulation vs. Measured Values
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DLSC Efficiency of Heat Extraction
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Groundwater Flow Effects on SBTES Systems
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DLSC Parametric Evaluation (Perimeter Boreholes)
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Convection Effects on SBTES Systems
20
Saturated Soil Conditions with a Water Table at the Surface
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Convection Effects on SBTES Systems
21
Saturated Soil Conditions with a Water Table at the Surface
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Pilot SBTES System at Colorado School of Mines
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Simplified Numerical Analysis for DesignAssumptions‐ Heat transfer is governed by
conduction
23
⋅
Boundary Conditions‐ Constant heat flux applied to the
boreholes‐ Heat flux estimated as follows:
‐ Thermally insulated layer at top‐ Initial soil temperature of 10°C
Model Geometry
Baseline Model Inputs ( = 30 W/m)Parameter
Volumetric flow rate, 0.3 (m3/s)
Temperature difference, ΔT 2 °C
Borehole length 10 m
Heat exchanger diameter 0.025 m
∆2
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Results: Impact of Borehole Spacing24
5
10
15
20
25
30
35
0 10 20 30 40
Soil
tem
pera
ture
(°C
)
Distance (m)
1 23 45 7.510
q = 30 W/m2
90 daysSpacing (m)
.
Increasingspacing
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Results: Impact of Boundary Heat Flux 25
5
10
15
20
25
30
35
10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
2025303540
90 daysλ = 1.0 W/mKSpacing: 1 m
q (W/m2).
5
10
15
20
25
30
35
10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
2025303540
90 daysλ = 1.0 W/mKSpacing: 2 m
q (W/m2).
Spacing: 1.0 m Spacing: 2.0 m
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Results: Impact of Heating Duration26
Spacing: 1.0 m Spacing: 2.0 m
5
10
15
20
25
30
35
10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
90100110120
q = 30 W/m2
λ = 1.0 W/mKSpacing: 1 m
Time (days).
5
10
15
20
25
30
35
10 15 20 25 30So
il te
mpe
ratu
re (°
C)
Distance (m)
90100110120
q = 30 W/m2
λ = 1.0 W/mKSpacing: 2 m
Time (days).
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Results: Impact of Thermal Conductivity27
Spacing: 1.0 m Spacing: 2.0 m
5
10
15
20
25
30
35
10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
1.0
1.5
2.0
q = 30 W/m2
90 daysSpacing: 1 m
λ (W/mK).
Storagezone 5
10
15
20
25
30
35
10 15 20 25 30So
il te
mpe
ratu
re (°
C)
Distance (m)
1.0
1.5
2.0
q = 30 W/m2
90 daysSpacing: 2 m
λ (W/mK).
Storagezone
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Performance Variables: Temperature Density
28
Temperature Density, TD ( /m3) is defined as follows
is the average temperature of the soil ( )(m3) is the heat storage volume
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 2 4 6 8 10
Tem
pt. d
ensi
ty, T
D (°
C/m
3 )
Array spacing (m)
1.0
1.5
2.0
q = 30 (W/m2)90 days
λ (W/mK).
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Performance Variables: Heat Loss29
0.0
1.0
2.0
3.0
4.0
5.0
0 30 60 90 120
Late
ral h
eat l
oss (
GJ)
Time elapsed (days)
12345
q = 30 W/m2
90 daysλ = 1 W/mK
Spacing (m).
0.0
1.0
2.0
3.0
4.0
5.0
0 30 60 90 120La
tera
l hea
t los
s (G
J)
Time elapsed (days)
1.0
1.5
2.0
q =30 W/m2
90 daysSpacing: 1 m
λ (W/mK).
Lateral heat losses for: Different array spacing (left)
Different soil thermal conductivity values (right)
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Field Data from the CSM SBTES
Goals: 1. Perform a long‐term thermal response test on the system (Summer 2014)2. Monitor ambient cooling of system to evaluate losses (Fall 2014)
30
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Construction Pictures
Geothermal boreholes
Foam insulation
60 mil HDPE hydraulic barrier
Site soil
Manifold
31
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Heating Test Plan at Colorado School of Mines
32
Borehole 2 inletBorehole 2 outlet
Borehole 3 inletBorehole 3 outlet
Borehole 1 inletBorehole 1 outlet
Borehole 4 inletBorehole 4 outlet
Borehole 5 inletBorehole 5 outlet
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Results: Ambient and Fluid Temperatures
33
0
2
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
ΔT (°C)
Flui
d te
mpe
ratu
re (°
C)
InletOutletΔT
BH-2
0
2
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
ΔT (°C)
Flui
d te
mpe
ratu
re (°
C)
InletOutletΔT
BH-5
0100200300400500600700800900
1000
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Fluid flo
w ra
te (m
L/s)
BH‐1BH‐2BH‐3‐4‐5
0
2
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
ΔT (°C)
Flui
d te
mpe
ratu
re (°
C)
InletOutletΔT
BH-1
0
2
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
ΔT (°C)
Flui
d te
mpe
ratu
re (°
C) InletOutletΔT
BH-3
0
2
4
6
8
10
12
14
10
15
20
25
30
35
40
45
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
ΔT (°C)
Flui
d te
mpe
ratu
re (°
C)
InletOutletΔT
BH-4
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Results: Soil Temperatures
34
10
15
20
25
30
35
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Gro
und
tem
pera
ture
(°C
) T-A 2.3 mT-A 6.0 mT-A 7.8 mT-A 9.0 m
10
15
20
25
30
35
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Gro
und
tem
pera
ture
(°C
) T-B 2.3 mT-B 6.0 mT-B 7.8 mT-B 9.0 m
10
15
20
25
30
35
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Gro
und
tem
pera
ture
(°C)
T-C 2.3 mT-C 6.0 mT-C 7.8 mT-C 9.0 m
10
15
20
25
30
35
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Gro
und
tem
pera
ture
(°C
) T-D 2.3 mT-D 6.0 mT-D 7.8 mT-D 9.0 m
10
15
20
25
30
35
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Gro
und
tem
pera
ture
(°C
) T-E 2.3 mT-E 6.0 mT-E 7.8 mT-E 9.0 m
-30
-20
-10
0
10
20
30
40
50
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Air
tem
pera
ture
(°C
)MaximumAverageMinimum
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Results: Temperature Profiles
35
0
2
4
6
8
10
0 5 10 15 20 25 30 35
Dep
th fr
om su
rfac
e (m
)
Ground temperature, T (°C)
6/19/147/1/147/14/148/8/149/2/149/27/1410/22/1411/16/1412/27/14
Time (days) T-A0
2
4
6
8
10
0 5 10 15 20 25 30 35
Dep
th fr
om su
rfac
e (m
)
Ground temperature, T (°C)
6/19/147/1/147/14/148/8/149/2/149/27/1410/22/1411/16/1412/27/14
Time (days) T-B0
2
4
6
8
10
0 5 10 15 20 25 30 35
Dep
th fr
om su
rfac
e (m
)
Ground temperature, T (°C)
6/19/147/1/147/14/148/8/149/2/149/27/1410/22/1411/16/1412/27/14
Time (days) T-C
0
2
4
6
8
10
0 5 10 15 20 25 30 35
Dep
th fr
om su
rfac
e (m
)
Ground temperature, T (°C)
6/19/147/1/147/14/148/8/149/2/149/27/1410/22/1411/16/1412/27/14
Time (days) T-D0
2
4
6
8
10
0 5 10 15 20 25 30 35
Dep
th fr
om su
rfac
e (m
)
Ground temperature, T (°C)
6/19/147/1/147/14/148/8/149/2/149/27/1410/22/1411/16/1412/27/14
Time (days) T-E0
2
4
6
8
10
0 5 10 15 20 25 30 35
Depth from
surface (m
)
Ground temperature, T (°C)
06/01/1407/01/1408/01/1409/01/1410/01/1411/01/1412/01/1401/01/15
Tm,out = 12 °CTout = 15 °C = 0.54 W/mKCs = 1200 J/kgKs = 30 W/m2K=1.99×10‐7 s‐1
d=√(2a/)k=/(sd)=tan‐1(k/(1+k))
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Results: Temperature Profiles with Radius
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10
15
20
25
30
35
0 1 2 3 4 5 6
Gro
und
tem
pera
ture°
C
Distance from center borehole (m)
6/19/147/1/148/8/149/2/1410/22/1411/16/1412/27/14
Time (days) 2.3 m from surface
10
15
20
25
30
35
0 1 2 3 4 5 6
Gro
und
tem
pera
ture°
C
Distance from center borehole (m)
6/19/147/14/148/8/149/2/1410/22/1411/16/1412/27/14
Time (days) 7.8 m from surface
10
15
20
25
30
35
0 1 2 3 4 5 6
Gro
und
tem
pera
ture°
C
Distance from center borehole (m)
6/19/147/14/148/8/149/2/1410/22/1411/16/1412/27/14
Time (days) 6.0 m from surface
10
15
20
25
30
35
0 1 2 3 4 5 6
Gro
und
tem
pera
ture°
C
Distance from center borehole (m)
6/19/147/14/148/8/149/2/1410/22/1411/16/1412/27/14
Time (days) 9.0 m from surface
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Heat Flux and Ground Properties
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0
200
400
600
800
1000
1200
1400
6/19/2014 8/28/2014 11/6/2014 1/15/2015
Hea
t tra
nsfe
r rat
e (W
)
BoreholeAve. flow rate (0 to 49 days)
Ave. flow rate (49 to 75 days)*
Average heat injection rate
Thermal Conductivity (1‐4 days)
Thermal conductivity (12‐17 days)
Thermal conductivity(49‐75 days)
(ml/s) (ml/s) (W/m) (W/m K) (W/m K) (W/m K)1 500 300 18.6 0.48 0.52 0.552 50 30 18.5 0.45 0.55 0.543 150 83 23.1 0.56 0.54 0.664 150 83 19.4 0.55 0.57 0.555 150 83 19.3 0.54 0.57 0.55
0
10
20
30
40
50
1 10 100 1000
T flu
id, m
ean
(°C
)
Elapsed time (hours)
outinfff TTCVQ
1
ln4
tddT
LQ
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Analysis: Numerical vs Experimental
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Analysis: Heat Balance
39
Conservation of Energy
Injected Heat
Heat stored (Claesson and Hellstrom 1981)
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Scalability of SBTES Systems
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T T T
Distance from center
Distance from center
Distance from center
Single borehole
Smallest‐scale array
Full‐scale array
End of heat
injection period
End of rest period
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Scalability of SBTES Systems: Arrays Considered
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Scalability of SBTES Systems: Arrays Considered
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1011121314151617181920
0 5 10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
InjectionRestInitial
q = 30 W/m2
90 daysλ = 1.0 W/mK
.
1011121314151617181920
0 5 10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
InjectionRestInitial
q = 30 W/m2
90 daysSpacing: 2.5 mλ = 1.0 W/mK
.
1011121314151617181920
0 5 10 15 20 25 30
Soil
tem
pera
ture
(°C
)
Distance (m)
InjectionRestInitial
q = 30 W/m2
90 daysSpacing: 2.5 mλ =1.0 W/mK
.
Array 1
Array 3
Array 2
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Scalability of SBTES Systems: Arrays Considered
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0
1
2
3
4
5
6
7
0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
Hea
t sto
red
afte
r inj
ectio
n (G
J)
λ (W/mK)
13 BHs5 BHsSingle BH
q = 30 W/m2
90 days injection
.
0
1
2
3
4
5
6
7
0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
Hea
t sto
red
afte
r res
ting
(GJ)
λ (W/mK)
13 BHs5 BHsSingle BH
q= 30 W/m2
90 days resting
.
Storage After Heat Injection Storage After Resting Period
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Scalability of SBTES Systems: Arrays Considered
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0
5
10
15
20
25
20 30 40 50 60 70 80 90 100
Hea
t sto
red
(GJ)
qin (W/m2)
13BHs90 daysSpacing: 2.5 mλ = 1.0 W/mK
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New SBTES Site at UCSD
45
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Planned Borehole Array
46
1.5 m
Borehole heat exchanger
Thermistor string
0.75 m
3.0 m
1.5 m
6.0 m
0.75 m
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Planned Borehole Array
47
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Final Comments
• SBTES systems can effectively store heat in the subsurface
• Efficiency of heat extraction is low, but the heat source is renewable and nearly free
• Heat storage is best in soils with low thermal conductivity and with low permeability (low convection)
• Closer spacings (1‐2 m) will result in the greatest concentration of heat
• Sufficient boreholes are required in an array to retain elevated ground temperatures after a resting period
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