thermal response test and soil geothermal modelling

Thermal response test and soil geothermal modelling

Authors:

Pedro Rico López

Miguel Salgado Pérez

David Canosa Vaamonde

Martín Amado Pousa

Supervisors:

María Pagola

Inga Sorensen

Henrik Bjørn

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1. INTRODUCTION

Text

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Energy park

LOCATION

1. INTRODUCTIONVIA University

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LOCATION

ENERGY PARK

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1. INTRODUCTION

ENERGY PARK

LOCATION

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ENERGY PARK

1. INTRODUCTION

ENERGY PARK

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LOCATION

1. INTRODUCTION

ENERGY PARK

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LOCATION

1. INTRODUCTION

ENERGY PARK

VIA 14 VIA 13

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BOREHOLE DESCRIPTION

1. INTRODUCTION

VIA 14 VIA 13

VIA 14

100m 96m

10m

1. INTRODUCTION

�TRT in BHE VIA 14

�Thermal energy storage modelling with Feflow

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GOALS

GeRT

VIA 14

1. INTRODUCTION

�TRT in BHE via 14

-Thermal conductivity of the soil around of BHE VIA 14

-Borehole thermal resistance of the BHE VIA 14

Outcomes

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GOALS

Interpreted

Compared

Previous TRTBy intervals of timeGeRT software

Conclusions

1. INTRODUCTION

•Thermal modelling by feflow software

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GOALS

Behaviorof the soil

Storage Extraction

2. BIBLIOGRAPHIC RESEARCHVIA University

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Shallow geothermal energy

Energy stored in the form of heat

beneath the surface of the solid earth.

Solar = 1 MWh/m²

Geothermal = 0,5 – 1 kWh/m²

Solar : Geothermal = 1000 : 1

Shallow energy = Solar energy


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Shallow geothermal energy

• How much energy can be extracted depends on:

Heat transfer:

• Conduction

• Convection

• Advection

• Dispersion

• Radiation

Geothermal gradient:

• 2,5 – 3,0 ºC/100m

Properties of soil:

• Specific heat capacity

• Thermal conductivity

• Diffusivity

Conductive heat flow:

• 65 – 101 mW/m²


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Ground Source Heat Pump

Ground source


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Ground source heat pump system

The heat transfer is done through heat exchanger

Ground water heat pump system (open loops)

Close loops system


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Borehole heat exchanger

Ø 75-200 mm

30

-30

0m

de

pth


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Borehole heat exchanger

Configuration


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Borehole thermal resistance

The thermal resistance [K m W-1] is the capacity of any material to oppose to heat transfer through itself

Surrounding ground thermal resistance Rg


Rb= Rf + Rbhf+ Rbhw


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Parameter Influencing thermal resistance

•Number of pipes

•Borehole depth

•Shank spacing (distance between pipes)

•Pipe material

•Fluid flow rate


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TRT Definition

The thermal response test is a suitable method todetermine the effective thermal conductivity of theunderground and the borehole thermal resistance(Gehlin 2002).

Mogensen (1983) presented a method measure thethermal properties of boreholes in situ, the thermalresponse test.

Mogensen designed a system where a fluid is circulatedthrough the BHE. TRT method is based in the principle thatwith a known input power and tracking the meantemperature development over time, it is possible tomeasure the heat transported to the ground.


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Thermal response test TRT

Steps before TRT:

•Estimate thermal conductivity (λ) and volumetric heat capacity of the ground (Rb).

•Measure the undisturbed ground temperature.


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Underground thermal energy storage (UTES)

• Use of borehole heat

exchangers

• Depends on the thermal properties

of the ground.

• Can be used to balance heating

systems STES

3. EXPERIMENTAL SECTIONVIA University

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PROCESS SUMARY

• Thermal properties estimation.

• Undisturbed ground temperature.

• Thermal Response Test.

• Literature values from VDI

• Geological information (GEUS)

• Previous results of needle prove tests

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THERMAL PROPERTIES ESTIMATION

3. EXPERIMENTAL SECTION

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Depth (m) Layer thickness

(m)λ (W/mK)

Svc (MJ/m³K)From To

1 3 2,0 1,54 2,40

3 6 3,0 1,00 1,60

6 9 3,0 2,36 2,20

9 12 3,0 1,40 1,90

12 15 3,0 1,00 1,50

15 18 3,0 2,35 2,50

18 24 6,0 1,40 1,90

24 27 3,0 1,74 2,40

27 45 18,0 1,00 2,00

45 48 3,0 1,31 2,00

48 51 3,0 1,10 2,00

51 54 3,0 1,80 2,40

54 57 3,0 2,40 2,50

57 100 43,0 1,00 2,00

Total depth (m) 99,0

λ(ari) Svc(ari)

1,23 2,03

Arithmetic mixing model;


Thermal conductivity:

Volumetric heat capacity:

λ= 1,23 W/m/K

Svc= 2,03 MJ/m³/K

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• This values are not a good estimation

• λ Significantly lower than real

• Only to calculate break time for steady state


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UNDISTURBED GROUND TEMPERATURE

A good estimate of the undisturbed ground

temperature is necessary for a correct design of the

ground heat exchanger (Gehlin 2002).

• At the same time the authors measured the

ground water table at 15,05m.


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The method performed was:

• Measure temperature in each meter of depth.

• 4 minutes interval between steps.

• The average temperature calculated with the

arithmetic mean.


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The undisturbed ground

temperature mean result was

9,56 ºC

0 5 10 15

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Temperature (Cº)

Depth

(m)


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THERMAL RESPONSE TEST

Analysis method – Line Source Theory


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Experimental setup for TRT

• Equipment

- New equipment GeRT by UBeG

- Safety control systems

- Own software


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• Initial assumptions

- Temperature of soil in equilibrium

- Insulate the pipes

- Pressure between 1 and 2 bar

- Turbulent flow Re> 4000

- Heat power of 30-80 W/m

- Length minimum 50 h


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• Calculations

- Total duration: 50,8 h

- Reynolds number: 17020

- Heat input rate: 58 w/m

- Initial ti: 9,6 ºC

- Final tf: 24,9 ºC

Starting values Final values

Input temperature

9,62 ºC 26,56 ºC

Output temperature

9,63 ºC 23,43 ºC

Selected heating power

75% -

Date 07/04/2014 09/04/2014

Time 11:03 13:00Actual heating power

5,8 Kw 5,7 Kw

Flow rate 1,572 m3/h 1,572 m3/h

Total flow volume

283,90 m3 361,94 m3

Total electric work

673 Kwh 958 Kwh

Pressure 2 bar 2 bar


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• Calculations

- Length minimum 50 h

- Dismissing time

- Time intervals

VIA 14 CALCULATIONS

Timeinterval

6h-50h 9h-50h 12h-50h 9h-45h 9h-40h


4. RESULTS, INTERPRETATION AND

COMPARIONS OF TRT

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Results

Undisturbed Ground

Temperature (°C)

Mean power rate input

(W/m)

Thermal Conductivity

(W/mK)

Borehole Thermal

Resistance (mK/W)

9,56 56,85 2,03 ± 0,03 0,1079 ± 0,0020

0,00

5,00

10,00

15,00

20,00

25,00

30,00

0 5 10 15 20 25 30 35 40 45 50 55

Time (h)

Tf(°C) LHS (°C) Effect (kW) Flow (m³/h)


COMPARIONS OF TRT

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y = 2,2229x - 1,9832

20,50

21,00

21,50

22,00

22,50

23,00

23,50

24,00

24,50

25,00

25,50

10,25 10,50 10,75 11,00 11,25 11,50 11,75 12,00 12,25

Tem

pe

ratu

re (

ºC)

Time ln(s)

Temperature (ºC) Linear (Temperature (ºC))


COMPARIONS OF TRT

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��

��

�

��

��

�

�

��

��

��

According line source theory:

0,0750

0,0800

0,0850

0,0900

0,0950

0,1000

0,1050

0,1100

0,1150

0,1200

0,1250

0,1300

0,1350

0,1400

0,1450

0,1500

1,50

1,55

1,60

1,65

1,70

1,75

1,80

1,85

1,90

1,95

2,00

2,05

2,10

2,15

2,20

2,25

7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5 52,5

The

rmal

res

ista

nce

(mK

/w)

The

rmal

con

duct

ivity

(W

/mK

)

Time (h)

Soil thermal conductivity (w/mK) Borehole thermal resistance (mK/w)


COMPARIONS OF TRT

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λmean = 2,03 ± 0,03 w/mK

Rbmean = 0,1079 ± 0,0020 mK/w


COMPARIONS OF TRT

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Comparison time intervals

Time interval (h)

6-50 9-50 12-50 9-45 9-40


(W/mK)2,00 ± 0,03 2,03 ± 0,03 2,08 ± 0,03 2,05 ± 0,03 2,03 ± 0,03

Borehole Thermal

Resistance (mK/W)

0,1060 ± 0,0020 0,1079 ± 0,0020 0,1101 ± 0,0020 0,1088 ± 0,0019 0,1079 ± 0,0019

� ��

∝= 8,89 hours

According Sanner (2005) and Banks (2012):


COMPARIONS OF TRT

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y = 2,2643ln(x) + 16,076

y = 2,2229ln(x) + 16,219

y = 2,1768ln(x) + 16,381

20,00

20,50

21,00

21,50

22,00

22,50

23,00

23,50

24,00

24,50

25,00

5,00 50,00

Tem

pera

ture

(°C

)

Time logarithm (h)

Trend Line (6-50h) Trend Line (9-50h) Trend Line (12-50h)


COMPARIONS OF TRT

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Comparison GeRT software


COMPARIONS OF TRT

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COMPARIONS OF TRT

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Time interval (h)

Manual calculation

GeRT calculation

Neglected time(h)

9,00 8,96


(W/mK)2,03 2,01

Borehole Thermal Resistance

(mK/W)0,1079 0,1090

Error in manual results ≈ 1%


COMPARIONS OF TRT

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Time interval (h) Past TRT Current TRT

Starting Date 03/07/2013 07/04/2014

Starting time 18:00 10:10

Finishing date 07/07/2013 09/04/2014

Finishing time 16:33 13:00

Total duration (h) 51,25 50,8

Undisturbed ground

temperature (ºC)9,90 9,56

Groundwater level (m) 15,15 15,05

Average heating

power (w)2180 5626

Average flow rate (l/h) 1121,70 1554,75

Comparison with previous TRT


COMPARIONS OF TRT

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0,0

2,5

5,0

7,5

10,0

12,5

15,0

17,5

20,0

22,5

25,0

27,5

-5 0 5 10 15 20 25 30 35 40 45 50 55

Time (h)

Past TRT temperature (ºC) Current TRT temperature (ºC) Past TRT power (Kw) Current TRT power (Kw)


COMPARIONS OF TRT

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y = 0,9748x + 4,356

y = 2,2229x - 1,9832

14

15

16

17

18

19

20

21

22

23

24

25

26

10,25 10,50 10,75 11,00 11,25 11,50 11,75 12,00 12,25

Tem

pera

ture

(ºC

)

ln (s)

Past TRT Present TRT Linear (Past TRT) Linear (Present TRT)


COMPARIONS OF TRT

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0,10

0,11

0,12

0,13

0,14

0,15

1,00

1,25

1,50

1,75

2,00

2,25

9 14 19 24 29 34 39 44 49 54

Bo

reh

ole

th

erm

al r

esi

sta

nc

e (

mK

/w)

So

il th

erm

al c

on

du

cti

vit

y (

w/m

K)

Time (h)

λ past TRT λ present TRT Rb past TRT Rb Present TRT


COMPARIONS OF TRT

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Heating power

Flow rate≈ Constant in both TRT

Presence of air in the loop

Results Previous TRT Current TRT

Thermal Conductivity (W/mK)

1,75 ± 0,05 2,03 ± 0,03

Borehole Thermal Resistance (mK/W)

0,1128 ± 0,0049 0,1079 ± 0,0020

λpast TRT

too variable


COMPARIONS OF TRT

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Comparison with FEFLOW model

λ (w/mK) 2,03

Svc (MJ/m3K) 2,03

Temperature (ºC) 9,56

Area (m2) 20 x 20

Depth (m) 120

Groundwater

flowNeglected


COMPARIONS OF TRT

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Time

interval

(h)

λ grouting

(w/m·K)

Shank

spacing

(mm)

Svc soil

(MJ/m3·K)

Model 1 2,35 80 2,03

Model 2 1,50 80 2,03

Model 3 1,50 60 2,03

Model 4 1,50 60 3,00


COMPARIONS OF TRT

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9

11

13

15

17

19

21

23

25

27

0 5 10 15 20 25 30 35 40 45 50 55

Tem

pera

ture

(ºC

)

Time (h)

TRT Model 1 Model 2 Model 3 Model 4


COMPARIONS OF TRT

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Before starting TRT After finishing TRT


COMPARIONS OF TRT

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5. THERMAL ENERGY STORAGE

Soil data assumed:

• λ = 2,03 W/mK (real value of TRT)

• Svc = 2,03 MJ/m²K (literature value)

• Homogeneous characteristics

• Groundwater flow neglected

Thermal energy storage data assumed:

• Maximum soil temperature = 20 ºC

Thermal energy extraction data assumed:

• Minimum soil temperature = 0 ºC

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ENERGY STORAGE IN VIA 14 AND EXTRACTION IN VIA 13

Thermal energy extraction in BHE VIA 13

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Svc CALCULATIONS

∆T (K) Radius (m) Volume (m³) Energy (MJ) Energy(MWh)

-9,56 3,40 3486 -67660 -18,794

Svc 3,45 3590 -69665 -19,351

(MJ/m³K) 3,50 3695 -71699 -19,916

2,03 3,55 3801 -73762 -20,489

BHE depth 3,60 3909 -75854 -21,071

(m) 3,65 4018 -77976 -21,660

96 3,70 4129 -80127 -22,257

Taking into account a radio around the borehole between 3,50 and 3,55 m, the amount of energy can be extracted is between 19, and 20,5 MWh


Thermal energy storage in BHE VIA 14

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Svc CALCULATIONS

∆T (K) Radius (m) Volume (m³) Energy (MJ) Energy(MWh)

-9,56 3,10 3019 63984 17,773

Svc 3,20 3217 68178 18,938

(MJ/m³K) 3,30 3421 72506 20,141

2,03 3,40 3630 76997 21,380

BHE depth 3,45 3739 79247 22,013

(m) 3,50 3848 81561 22,656

96 3,60 4072 86288 23,969

Taking into account a soil radio around the borehole between 3,40 and 3,45 m, the amount of energy can be stored is between 21,4 and 22,0 MWh


· G · G · \ ·

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INFINITE LINE SOURCE METHOD

Applying Fourier’s Law in each direction and assuming that the thermal process depends only on the radial distance:

Integrating the previous formula and assuming that the temperature in the system at the beginning (t=0) and in the surroundings located at infinite distance from the heat source (r=∞) is constant (t0=undisturbed ground temperature)


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Heat energy extraction in BHE VIA 13

Previous premises:

• Minimum soil temperature in storage (Tf)

• Undisturbed ground temperature (T0)

• Time = 1 year

Heat energy extraction (BHE VIA 13)

r (m) λ(W/m K)

Rb (m K/W)

SVC (J/m³ K)

a (m²/s) Tf (ºC) T0 (ºC) γ (Euler’s constant)

0,16 2,03 0,0899 2030000 0,000001 0,0 9,56 0,5772157

Isolating from the LS formula:

• q: heat flux (W/m)

• Q: amount of heat energy extracted (MWh)


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Heat energy storage

along 1 year

Q = - 20,07 MWh


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Heat energy storage in BHE VIA 14

Previous premises:

• Minimum soil temperature in storage (Tf)

• Undisturbed ground temperature (T0)

• Time = 1 year

Heat energy extraction (BHE VIA 13)

r (m) λ(W/m K)

Rb (m K/W)

SVC (J/m³ K)

a (m²/s) Tf (ºC) T0 (ºC) γ (Euler’s constant)

0,16 2,03 0,1079 2030000 0,000001 20,0 9,56 0,5772157

Isolating from the LS formula:

• q: heat flux (W/m)

• Q: amount of heat energy extracted (MWh)


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Heat energy storage

along 1 year

Q = 21,85 MWh


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FEFLOW geothermal modelling

ENERGY STORAGE IN VIA 14 AND EXTRACTION IN VIA 13

Theoretical situation model:

• Heat energy extraction through BHE VIA 13

• Heat energy storage through BHE VIA 14

• Time of simulation: 1 year

• Time step of simulation: 10-7seconds

• Heat flux (W/m) obtained from LS model per day during 1 year

• Minimum flow rate to obtain turbulent flow

• Soil data assumed:• λ = 2,03 W/mK (real value of TRT)

• Svc = 2,03 MJ/m²K (literature value)

• Homogeneous characteristics along depth (groundwater flow neglected)

• Undisturbed ground temperature (9,56 ºC)


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FEFLOW extraction and storage model

The evolution of the BHEs temperatures is according to the main premises established before de calculation of the heat flux along the year.


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Soil temperature behaviour along 1 year


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Influence on the soil temperature of the heat energy extraction through the BHE VIA 13 and the heat energy storage to BHE VIA 14 along 1 year.

• NO heat transfer between the BHE during 1 year.



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SEASONAL THERMAL ENERGY STORAGE IN BHE VIA 14

Theoretical heating system model:

• Heat energy consumption of the World Flex House in Energy Park

(heating system and DHW)

• Heat pump (COP = 4,65) connected to the BEH VIA 14 and thermal solar panels

• Four 2,5 m² area and 0,79 of optical efficiency thermal solar panels

• Excess production of thermal solar panels is stored within the soil through the BHE


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SEASONAL THERMAL ENERGY STORAGE IN BHE VIA 14

Thermal solar panels Heat pump (COP = 4,65)

Sun radiation (kWh/m²)

Heat energy production (kWh)

Storage: excess production (kWh)

Consumption (kWh)

Extraction(kWh)

Jan 29,1 166,3 0,0 1501,7 1235,9

Feb 44,8 256,1 0,0 960,9 790,8

Mar 112,0 640,2 0,0 247,8 203,9

Apr 158,0 903,2 506,2 0,0 0,0

May 174,0 994,7 794,7 0,0 0,0

Jun 170,0 971,8 771,8 0,0 0,0

Jul 167,0 984,6 754,6 0,0 0,0

Aug 152,0 868,9 668,9 0,0 0,0

Spe 119,0 680,3 282,3 0,0 0,0

Oct 78,7 449,9 41,9 0,0 0,0

Nov 37,8 216,1 0,0 875,9 720,9

Dec 23,5 134,3 0,0 1497,7 1232,6

YEAR 1265,9 4824,3 3820,3 5083,9 4184,1


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BHE temperatures evolution along the year

• Heat energy extraction in winter months

• Heat energy storage in summer months

FEFLOW heating system model along 1 year


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FEFLOW heating system model along 1 year

Soil temperature behaviour along 1 year


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FEFLOW heating system model

Temperature of the soil in 31th of January

This figure shows the cooling of the ground after the first month of heat energy extraction


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Temperature of the soil in 31th of May

This figure shows how the temperature of the ground is balanced after the second month of heat energy storage


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Temperature of the soil in 30th of September

This figure shows the heating of the temperature of the ground after the heat storage season


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Temperature of the soil in 31th of December

This figure shows the cooling of the ground after the second month of heat energy extraction


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FEFLOW heating system model along 3 years

BHE temperatures evolution along 3 year

• Heat energy extraction in winter months

• Heat energy storage in summer months


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Stored heat energy into the soil obtained from FEFLOW


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Stored heat energy into the soil influence:

• Heat energy extraction: 12552,3 MWh

• Heat energy storage: 11460,9 MWh

• Stored heat energy into the soil drops 2300 MWh after 3 years

• FEEFLOW theoretical heat energy storage

12552,3 – 2300 = 10252,3 MWh

• Efficiency of the thermal energy storage = 89,5 %


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INTERPRETATION OR RESULTS


• Line source model: 20,07 MWh during 1 year

• Cooling from 9,56 ºC to 0 ºC of a cylinder of soil with radio between 3,50 and 3,55 m

• Soil is an infinite medium: After 1 year, around 1 m of the BHE, the temperature soil drops until 4,0 ºC


• Line source model: 21,85 MWh during 1 year

• Heating from 9,56 ºC to 20 ºC of a cylinder of soil with radio between 3,40 and 3,45 m

• After 1 year, considering the influence around 1 m of the BHE, the temperature soil increases until 13,5 ºC


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INTERPRETATION OR RESULTS

Seasonal energy storage in BHE VIA 14

• The ground source heat pump system efficiency improves (higher flow temperatures)

• Soil temperatures are balanced along the time (NO freezing problems within the soil)

• Heat energy stored into the soil along the time is balanced


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• VIA University is a leading university researching about

shallow geothermal energy

• VIA has great facilities to develop research projects

• For TRT, Svc estimation is one of the main problems leaving

the door open to research in this field

• Use of real data of Energy Park installations in further projects

and compare FEFLOW simulations with real experiments

• Take into consideration more data (ground water flow)

• Implement better managing procedures for the

collaboration between project group researches

6. CONCLUSIONS AND

FURTHER RESEARCH

Thank you for your attention

Contact info:

Pedro Rico López – [email protected]

Miguel Salgado Pérez – [email protected]

David Canosa Vaamonde – [email protected]

Martín Amado Pousa – [email protected]

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thermal response test and soil geothermal modelling

Engineering

solar energy

shallow energy

thermalresponse test

trt method

suitable method todetermine

c100mproperties of soil

introductionthermal

rf rbhf rbhw