Modelling Thermal Energy Storage
in closed loop systems:
Potential effects on Southern Ontario aquifer
chemistry and implications
Canadian Geoexchange Coalition
3rd Business & Policy Forum
November 17 – 18, 2008
Carlos Jurado
Career Bridge - Ontario Ministry of the Environment
1
Presentation Outline
• Background:
• Closed loop Geoexchange systems review
• Case study: Cumulative temperature of ground water and
migration beyond well field
• Objectives of Modelling Study
• Modelling study description:
• Effects of temperature accrual in ground water chemistry
parameters pH, pE and mineral saturation indices
• Interpretation of results
• Findings and potential implications
2
Background:
Small closed loop vertical system
Advantages:
•Relatively small ground area required
•Little variation in temperature and thermal
properties of subsurface at working depths
•Smallest pipe length and pumping energy
required
• May yield the most efficient system
performance
Potential issues:
• Higher installation costs (borehole drilling)
• Limited supply of qualified installers.
1999 ASHRAE Applications Handbook. Chapter 31.
Geothermal Energy
3
Background:
Large scale closed loop systems
• Known as Borehole Thermal Energy Storage
(BTES) systems
• May reach depths >200 metres from surface
• High number of holes: UOIT = 384
Potential issues:
• Thermally imbalanced well field
• Ground water heat transport beyond property
boundaries
• Thermal interference on neighbouring systems
• Discharge of warmer out of season ground
water to surface water
Epstein and Sowers (2006). The Continued Warming of the Stockton
Geothermal Well Field. ECOSTOCK Proceedings.
Taken from UOIT - BTES website 2008
4
Background: Case Study
• Richard Stockton College, New Jersey, USA
Sowers et al. 2006. ECOSTOCK Proceedings
• Average net yearly thermal storage of 1oC in a large scale closed
loop system (i.e. temperature increases 1oC)
• Temperature peaks measured beyond the well field, along the
path of ground water flow
What is the environmental concern with
Large Scale Geoexchange systems?
5
Objectives of the Modelling Study
• Investigate the potential effects of temperature increase on
major physical - chemical parameters of ground water
• Investigate the potential effects of temperature increase on
mineral saturation indices of ground water
• Identify potential issues for future field scale research on
Aquifer Thermal Energy Storage systems
6
Modelling Study Description:
Chemical speciation in groundwater
• Phreeqc 2.0 used to model aqueous species formation
• Extensive database of minerals for speciation reactions:
WATEQ 4.0
• Simplicity of use to input water chemistry parameters
and simulate reactions
7
Modelling Study Description:
Sample selections and modelling criteria
• Ground water samples from drinking water well datasets
• Datasets with comprehensive water chemistry data
• Temperature range for aqueous speciation includes
operating temperature range for closed-loop systems
• Field values and major ions concentrations selected as
initial input parameters
8
Newmarket
Aurora
Toronto
Location of Ground Water well
source data:
Waterloo
Kitchener
Yonge street Aquifer :
Aurora and Newmarket
Mannheim Aquifer:
Kitchener and Waterloo
9
Simulated temperature increase effects on pH and pE values
9
8
pH
7
pH 1
pH and pE
6
pH 2
pH 3
5
• pH close to neutral or
slightly alkaline with
increased temperature
XXX
pE 1
4
pE 2
pE 3
3
2
• pE reducing tendency with
increased temperature
pE
1
0
0
5
10
15
20
25
30
35
40
45
50
o
Temperature C
10
Mineral Saturation Indices variation in ground water upon temperature increase
Aurora well
CaSO4
[Anhydrite] CaSO
Anhydrite
4
5
CaCO3
[Aragonite] CaCO
Aragonite
3
CaCO3
Calcite[Calcite]
4
CaCO3
CaMg(CO3)2
Dolomite (d) [Dolomite]
CaMg(CO3)2
CaMg(CO3)2
Dolomite (d) [Dolomite]
CaMg(CO3)2
3
Saturation Index
2
1
Dolomite
Magnesite
0
FeOOH
[Goethite]
Goethite
FeO(OH)
Fe(OH)2.7Cl.3
Akaganéite
Fe(OH)2.7Cl0.3
Fe(OH)3(a)
Bernalite (a)
Fe(OH)3
CaSO4
: 2H2O [Gypsum]
Gypsum
CaSO4·2H2O
Jarosite H
(H3O)Fe
(H3O)Fe3(SO4)2(OH)6
[Jarosite-H]
3(SO4)2(OH)6
Jarosite (ss)
(K0.77Na0.03H0.2)Fe
(K0.77Na0.03H0.2)Fe3(SO4)2(OH)6
[Jarosite-ss]
3(SO4)2(OH)6
-1
Jarosite K
KFe3(SO4)2(OH)6
KFe3(SO4)2(OH)6
[Jarosite-K]
-2
Jarosite Na
NaFe
NaFe3(SO4)2(OH)6
[Jarosite-Na]
3(SO4)2(OH)6
Magnesite
MgCO3
[Magnesite] MgCO3
-3
Melanterite [Melanterite]
FeSO4:7H2O
FeSO4:7H2O
-4
Nesquehonite
MgCO3:3H2O
MgCO3:3H2O
[Nesquehonite]
Siderite
FeCO3
[Siderite]
-5
0
5
10
15
20
25
30
35
40
45
50
FeCO3
Siderite (d) [ Siderite-d-3
FeCO3]
FeCO3(d)(3)
Temperature oC
11
Mineral Saturation Indices variation in ground water upon temperature increase
Newmarket well
Anhydrite
CaSO4 [Anhyd
5
CaSO4
Aragonite
CaCO3 [Aragonite] CaCO3
4
Calcite
CaCO3 [Calcite]
Dolomite
CaMg(CO3)2 (d)
3
CaMg(CO3)2
[Dolomite]
Dolomite
(d) [Dolomite]
CaMg(CO3)2
CaMg(CO3)2
2
Bernalite
Saturation Index
CaCO3
1
Dolomite (d)
Goethite
FeOOH [Goethite]
FeO(OH)
Akaganéite
Fe(OH)2.7Cl.3
Fe(OH)2.7Cl0.3
Bernalite
Fe(OH)3(a)(a)
Fe(OH)3
Gypsum
CaSO4·2H2O
CaSO4 : 2H2O [Gypsum]
0
Jarosite
H
(H3[Jarosite-H]
O)Fe3(SO4)2(OH)6
(H3O)Fe3(SO4)2(OH)6
Jarosite
(ss)
(K0.77Na0.03H[Jarosite-ss]
(K0.77Na0.03H0.2)Fe3(SO4)2(OH)6
0.2)Fe3(SO4)2(OH)6
-1
Jarosite
K
KFe3(SO4)2(OH)6
KFe3(SO4)2(OH)6
[Jarosite-K]
-2
Jarosite
Na
NaFe
NaFe3(SO4)2(OH)6
[Jarosite-Na]
3(SO4)2(OH)6
Magnesite
MgCO3 [Magnesite] MgCO3
-3
Melanterite
FeSO4:7H2O
FeSO4:7H2O [Melanterite]
Nesquehonite
MgCO3:3H2O
MgCO3:3H2O [Nesquehonite]
-4
Siderite
FeCO3 [Siderite]
-5
0
5
10
15
20
25
30
35
40
45
50
FeCO3
Siderite
(d) [ Siderite-d-3
FeCO
FeCO3(d)(3)
] 3
Temperature oC
12
Mineral Saturation Indices variation in ground water upon temperature increase
Waterloo well
5
CaSO4 [Anhydrite] CaSO
Anhydrite
4
4
CaCO3 [Calcite]
Calcite
CaCO3 [Aragonite] CaCO
Aragonite
3
3
CaMg(CO3)2
Dolomite
(d) [Dolomite]
CaMg(CO3)2
FeOOH [Goethite] FeO(OH)
Goethite
2
Saturation Index
CaCO3
CaMg(CO3)2 (d) [Dolomite]
Dolomite
CaMg(CO3)2
Bernalite
Dolomite (d)
1
Fe(OH)2.7Cl.3
Akaganéite
Fe(OH)2.7Cl0.3
Fe(OH)3(a)(a)
Bernalite
Fe(OH)3
CaSO4 : 2H2O [Gypsum]
Gypsum
CaSO4·2H2O
0
(H3O)Fe3(SO4)2(OH)6
Jarosite
H
(H3[Jarosite-H]
O)Fe3(SO4)2(OH)6
(K0.77Na0.03H0.2)Fe3(SO4)2(OH)6
[Jarosite-ss]
Jarosite
(ss)
(K0.77Na0.03H0.2
)Fe3(SO4)2(OH)6
-1
KFe3(SO4)2(OH)6
[Jarosite-K]
Jarosite
K
KFe3(SO4)2(OH)6
-2
NaFe3(SO4)2(OH)6
[Jarosite-Na]
Jarosite
Na
NaFe
3(SO4)2(OH)6
MgCO3 [Magnesite] MgCO
Magnesite
3
-3
FeSO4:7H2O [Melanterite]
Melanterite
FeSO4:7H2O
-4
MgCO3:3H2O [Nesquehonite]
Nesquehonite
MgCO3:3H2O
FeCO3 [Siderite]
Siderite
-5
0
5
10
15
20
25
30
35
40
45
50
FeCO3
FeCO3(d)(3)
Siderite
(d) [ Siderite-d-3
FeCO] 3
o
Temperature C
13
Mineral Saturation Indices variation in ground water upon temperature increase
Kitchener well
Anhydrite
si_Anhydrite
Aragonite
si_Aragonite
5
CaCO3
Calcite
CaCO3
si_Calcite
Dolomite
si_Dolomite(d) CaMg(CO3)2
4
Dolomite
(d)
si_Dolomite
Goethite
si_Goethite
3
2
Saturation Index
CaSO4
Bernalite
1
Dolomite (d)
Dolomite
0
CaMg(CO3)2
FeO(OH)
Akaganéite
Fe(OH)2.7Cl0.3
si_Fe(OH)2.7Cl.3
Bernalite
(a)
Fe(OH)3
si_Fe(OH)3(a)
Gypsum
si_Gypsum
Jarosite
H
si_JarositeH
CaSO4·2H2O
(H3O)Fe3(SO4)2(OH)6
Jarosite
(ss)
(K0.77Na0.03H0.2)Fe3(SO4)2(OH)6
si_Jarosite(ss)
Jarosite
K
KFe3(SO4)2(OH)6
si_Jarosite-K
-1
Jarosite
Na
NaFe3(SO4)2(OH)6
si_Jarosite-Na
Magnesite
si_Magnesite MgCO3
-2
Melanterite
si_Melanterite FeSO4:7H2O
-3
Nesquehonite
si_NesquehoniteMgCO3:3H2O
Siderite
si_Siderite
-4
FeCO3
Siderite
(d)
FeCO3
si_Siderite(d)(3)
-5
0
5
10
15
20
25
30
35
40
45
50
Temperature oC
14
Findings from modelled
predictions:
• Carbonate minerals containing either Calcium, Magnesium or Iron
tend to precipitate with increase in temperature
• Bernalite [Fe(OH)3] shows a tendency to dissolve with increased
temperature
• Other minerals do not show saturation crossovers with same frequency
as those above
15
Implications of modelled
predictions:
• Supersaturation of carbonate minerals may lead to precipitation,
intensifying the scaling problem in a geoexchange system
• Subsaturation of Bernalite (iron hydroxides) may lead to dissolution
of iron compounds and adsorbed anions (e.g. arsenic)
• Potential focus of research could be the mobility and concentrations of
metalloid species, particularly in subsurface with reducing conditions;
the impacts of thermal discharge of groundwater to surface water and
assessing the effects of warmer subsurface on climate change.
16
Acknowledgments:
• Career Bridge Organization, funded by the
Ontario Ministry of Citizenship and Immigration
• Ontario Ministry of the Environment
• Canadian Geo-exchange Coalition
17