establishing geothermal energy research at university ... · establishing geothermal energy...

Establishing Geothermal Energy Research at

University College Dublin

Engineers Ireland Geotechnical Engineering Society, Civil

Engineering Society & International Association of Hydrogeologists

Event

January 2013

Dr Phil Hemmingway UCD School of Biosystems Engineering

Presentation Outline

1. Ground Source Energy System Types

2. Open Loop Investigations (Chemistry & Settlement)

3. Thermal Response Testing (TRT)

4. Laboratory Thermal Characterization Equipment

5. Energy Foundations

6. Finite Element Analyses

7. Concluding Remarks & Contact Details

Ground Source Energy

Five of the main types of Ground Source Energy System

Current research focus is primarily on closed loop

boreholes & energy piles – initially open loop

Open Loop Investigations

Water Chemistry & Settlement (Cork Docklands)

Not routinely investigated

Aware of pumping tests in the area

Settlement: Highly compressible alluvium means

pumping induced settlement possible

Chemistry: Potentially an issue due to former

industrial use of site & saline intrusion


Settlement Calculations

Refer to “Geotechnical and structural aspects of

open loop geothermal systems” by Mike Long from

GAI conference 2008

Settlement is a potential issue for open loop systems

but it is entirely predictable and mitigation techniques

are well established to deal with the consequences

For Gravels For Clays


Water Chemistry Results (Cork Docklands)

*Based on BS EN 15450:2007 & other publications

Parameter Measured Required* Comment

pH Value 5.57 6.5 to 9.0 Lower Values = Typically Higher

Corrosion Rates

Chloride

(ppm) 5,660 < 300

Issues for HP’s with Stainless Steel,

Copper, Cupro-nickle or Titanium

Elec.

Conductivity

(μS/cm)

19,325 50 to 1,000 Drinking Water ≈ 5 – 500 μS/cm

RSI (Ryznar

Stability) 7.9 5 to 7 Indicative of “Heavy Corrosion”

LSI (Langelier

Saturation) - 1.1 - 0.5 to 0.5

- 0.5 = Slightly Corrosive;

- 2.0 = Serious Corrosion


Some Open Loop Issues to Consider

Well Reliability (Pumping Tests)

Investigate Water Chemistry

RA of Surrounding Wells / Aquifer(s)

Calculate Potential Settlement

Thermal Plume (e.g. London)

Disposal Mechanism

Further Reading: Hemmingway, P & Long, M. 2011. Geothermal Energy: Settlement and

Water Chemistry in Cork. Proceedings of ICE Engineering Sustainability, 164(ES3), 213-224

Thermal Response Testing (In Situ)

Known quantity of heat energy is injected

into (or extracted from) heat exchange

piping

Temperature development of the

circulating fluid is monitored

A TRT Provides Information on:

Ground Thermal Conductivity (λ)

Borehole Thermal Resistance (Rb)

Initial Ground Temperature

Groundwater Flow Conditions

(Design Implications)

TRT: Test Rig Operation

1. Heat transfer fluid is circulated

by a pump

2. Heat energy is added to the

fluid by resistance heaters

3. ‘Injected’ fluid temp. measured

4. Fluid circulates around a

closed loop in the ground

5. ‘Return’ fluid temp. measured

6. Fluid re-circulated by the

pump

A TRT continues (typically over a number of days) until ‘steady-state’

conditions are achieved.

Further Reading: Hemmingway, P & Long, M. 2012. Design and Development of a Low-Cost

Thermal Response Rig. Proceedings of ICE Energy, 165(EN3), 137-148

Many Ways to Evaluate TRT Results

Analytical Line Source Method

Cylindrical Source Method

Other Numerical Methods

All Based on Fourier’s Law of Heat Conduction

The temperature response of a forcibly

heated or cooled material at a certain

location is proportional to its thermal

conductivity (q = heat flux W/m2)

TRT: Test Evaluation

Example 1. Undisturbed BHE



2. Transient BHE

Response – Temp

Development

Influenced Mainly by

Borehole Filling



2. Transient BHE

Response – Temp

Development


Borehole Filling

3. Start of Steady

State



2. Transient BHE

Response – Temp

Development


Borehole Filling

3. Start of Steady

State

4. Stable Heat Flow –

Temp Development

Influenced by Ground


Equation above

describes ‘The

Temporal Evolution

of the Mean Fluid

Temperature’

Therefore Can

Determine ‘k’ if Plot

Av. BHE Temp vs.

Ln(Time)


Example - LSM

Example - LSM Kelvin’s Line

Source Theory

can be written

as (EklÖf &

Gehlin, 1996):

Q = Heat Input (W)

H = BHE Depth (m)


TRT: Case Study

Development of 40 bed hospital with under-floor heating

GE to provide lead heating & cooling

Small gas boiler to cover

demand ‘peaks’

TRT1, TRT2 & TRT3 are

consecutive on one BH

Importance of thermal

gradient dissipation

Diff between estimate & ‘real’

conductivity (1.9W/mK) due

to presence of flint - quartz

Note effect on drilling costs

Further Reading: Hemmingway, P & Long, M. 2012. Thermal Response Testing of

Compromised Borehole Heat Exchangers. International Journal of Low-Carbon Technologies

Lab Thermal Conductivity Testing

Blue dots = measurement values

Red line = trend line….calc of T.C.

UCD Thermal Probe System:

Lab measurement of soil and soft rock;

ASTM standard available

x Require ~7inch rock core; Careful (&

sometimes time consuming) drilling of

core sample required

System Operation:

1. Probe inserted into test specimen;

2. Heat energy applied;

3. Time series temperature data

during heating measured by a

thermocouple;

4. Analysis of data.


UCD Single-Source Thermal System:

Lab measurement of concrete, grout

and soft soils

x Not suitable for measurement of hard

rock samples (difficult to prepare

required sample size)

System Operation:

1. Specimen is prepared to fit mould;


3. Temperature development measured

at several points within specimen;

4. Steady-state conditions are achieved;


Thermal

Grout

‘Standard’ s/c Grouts

Th

erm

al

Co

nd

ucti

vit

y


UCD Divided Bar Thermal System:

Good for lab measurement of rock

x Less suitable for measurement of soft

soil or concrete

System Operation:

1. Rock specimen prepared


3. Temperature development is

measured at several points within

specimen;

4. Steady-state conditions achieved;


Similar to UCD ‘Single-source’ system,

but higher accuracy due to better heating

control


Calculation of Thermal Conductivity:

Based on Fourier's Law of Heat

Conduction:

Q = λ x A x ΔT/ΔZ

Q = heat flow (W)

λ = thermal conductivity (W/mK)

A = cross sectional area (m2)

ΔT; ΔZ (see graphic)

Steady state: Assume Qr = Qs

Therefore, can calculate λs

Q = λs x As x ΔTs/ΔZs

Correction factors then applied

T1

ΔT1

T2

ΔT2

T3

ΔT3

T4

Reference

Copper

Heater I

Heater II

Copper

Copper

Reference

Sample

Copper

Load

ΔZr

ΔZr

ΔZs

40ºC

25ºC Steady state when T1, T2, T3 & T4

remain constant

Calculate Q from reference material

as we know λr

Q = λr x Ar x ΔT1/ΔZr

Energy Foundation Installation

Research Installation

a) Loop Preparation b) CFA Drilling


Research Installation

c) Loop Installation d) Pushing Last Few Feet


Lessons Learned

Schedule Small Number of Installations for First Day

of Piling Schedule

Contingencies for Unsuccessful Installations (FOS)

Tailor Concrete Mix Design (Aggregates & Viscosity)

Fill Pipes with Water to Counteract Buoyancy

Protection of Pipes During all Phases of Construction

Further Reading: Hemmingway, P & Long, M. 2011. Energy Foundations – Potential for

Ireland. American Society of Civil Engineers, GeoFrontiers, Dallas, USA, 460-470

Case Study: Undergraduate Project

Investigation of (some of the) parameters controlling

thermal conductivity in concrete mixes

Important so that the thermal

parameters of ‘energy foundations’

can be optimised

Parameters investigated include:

water-cement ratio

sand-cement ratio

aggregate type

aggregate properties

UCD Research Energy

Foundation Installation

Case Study: Undergraduate Project

Sample Results: Effect of water-cement ratio

Close to linear increase in thermal

conductivity with decreasing w-c

ratio

0.0

2.0

4.0

6.0

0.2 0.3 0.4 0.5 0.6

Th

erm

al C

on

du

cti

vit

y

(W/m

K)

Water-cement (w-c) ratio

0

10

20

30

40

0.2 0.3 0.4 0.5 0.6

Co

mp

Str

en

gth

(M

Pa)

Water-cement (w-c) ratio

Concrete compressive strength also

increases with decreasing w-c ratio

This suggests that lower w-c ratios

provide higher conductivity and

higher strength However: remember that the pile

needs to be workable enough to

insert piping and ancillary

equipment - need to find the

appropriate balance

Finite Element Analysis

Research Question: If water flow is present at the site of

a proposed geothermal system, what effect on:

Interaction between boreholes on site

Neighbouring sites – future installations

Current design practice – commercial software limitations

Step 1: Develop FEM ‘conduction model’

Step 2: Verify performance

Step 3: Develop model to handle convection effects

Step 4: Compare sub-surface thermal regimes

Step 5: Develop from sub-surface to ‘holistic’ model

Step 6: Validate against installed system

Approach taken:


Development & performance verification of conduction

model

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 5 10 15 20 25 30

Dif

fere

nce (

%)

Time (months)

0.25m

0.50m

1.0m

2.0m3.0m

(f)

20m

20

m

Comparison against

well known radial heat

flow theory:

Small differences: radial

heat flow equation does

not take account of

borehole backfilling

Conduction Only

No g.w. Flow

Conduction & Convection

g.w. Flow = 0.16 m/day

Water Flow


Modelled Scenario 1:

Single borehole configuration

One month time steps

Two year time frame

Further Reading: Hemmingway, P & Tolooiyan, A. 2013. Numerical and Finite Element

Analysis of Heat Transfer in a Closed Loop Geothermal System. Intl. J. Green Energy

Conduction Only

No g.w. Flow

Conduction & Convection

g.w. Flow = 0.16 m/day

Water Flow


Modelled Scenario 2:

Multi borehole configuration

One month time steps

Two year time frame

Further Reading: Tolooiyan, A. & Hemmingway, P. 2012. The Effect of Groundwater Flow on

the Thermal Front Created by Borehole Heat Exchangers. lntl. J. Low-Carbon Technologies


Modest groundwater

flow can have a

significant effect on

propagation of

thermal regime

FEM model capable

of quantifying this has

been constructed

Future Improvements: 3D functionality; develop into ‘holistic

model’ & validate against installed system (ongoing!)

Concluding Remarks

Summary of geothermal research in UCD Schools of

CSEE & Biosystems Engineering – others in UCD &

other research institutions

Current geothermal research team: Phil Hemmingway,

Mike Long, Turlough McGuinness & Tim Waters

Funding available – industry linked research

Publications available (free of charge) at:

www.ucd.ie/eacollege/biosystems/staff/academic

http://www.ucd.ie/eacollege/biosystems/staff/academic

Thank you for your interest

Please feel free to direct any comments,

queries or collaboration enquiries to

[email protected] or

[email protected]

UCD Biosystems Engineering Masters Course Enrolment - Sept 2013:

Sustainable Energy & Green Technologies

Other courses also available, please visit website:

www.ucd.ie/eacollege/biosystems

mailto:[email protected]



http://www.ucd.ie/eacollege/biosystems

establishing geothermal energy research at university ... · establishing geothermal energy...

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