HEAT TRANSFER EXPERIMENT IN THE GROUND WITH … · HEAT TRANSFER EXPERIMENT IN THE GROUND WITH ......

HEAT TRANSFER EXPERIMENT IN THE GROUND WITH

GROUND WATER ADVECTION

1/27

T. Katsura *1 K. Nagano*1 S. Takeda *1 K. Shimakura*1 Graduate School of Engineering, Hokkaido University, Sapporo, Japan

Background

Recently, the GSHP system has been remarked in Japan as a system with large potential for reduction of CO2 emissions.

05

1 01 52 02 53 03 54 0

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

Uni

ts

Markets of the GSHP in Japan For Cooling, Heating, Hot water supply

For Snow melting

2004

The number of the GSHP systems installed in Japan is increasing

However, the number is still less than the ones of other countriesTo promote the GSHP system more effectively is required

T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1

2/27

In Japan, there are a lot of regions where sufficient ground water as a heat source or a heat sink is available

Background

Example –Measured ground water level and ground water flow direction-

Almost Japanese cities are developed in alluvial fan area In this area, ground water flow is normally generated due to difference of the ground level

(Fujii et al. 2005)

Akita Plain


3/27

Background

Effect of the ground water flow for performance of the GSHP system

Increase of extracted or injected heat

Reduction of length of the ground heat exchanger and initial cost

Ground water velocity : Small (or Nothing)

Ground water velocity : Large

Heat extraction

Heat extraction

Temperature is decreased

Temperature is stable


4/27

Background

As the new study, the authors…have carried out laboratory experiments as a first step to develop adesign tool for the GSHP system with the ground water flow

It is important to consider the ground water flow for design of the GSHP system

While, we have developed a design tool for the GSHP system

The tool considered only heat conduction for calculation of the ground temperature

Main menu window Output window

Design tool for the GSHP system


5/27

On the other hand, in order to take - in a design of the GSHP system -the ground water flow into consideration, accurate measurements of the ground water velocity field are very important

Borehole (Ground heat exchanger)

Observation well(s) to measure ground water velocity

Applying new method

Not need

Background

However…

The authors propose a new method to estimate the ground water velocity.

Observation wells to measure ground water velocity is required apart from boreholes used as ground heat exchangers

Making the observation wells takes a lot of time and cost


6/27

Today’s topics

Thermal response for a heat source in the ground with the ground water flow

1. Laboratory experiments with a thermal probeInvestigate

2. Comparison between thermal responses of the measurement and calculations

The result of theoretical calculation and numerical calculationValidate

3. A new method to estimate the ground water velocityOutline of the method and its example


7/27

Schematic diagram

P

ON/OFF

Temperature measured point (Thermo couple)

Water flow direction

Sand filled layer (Silica sand)

Thermal probe

Water

Nonwoven fabric+ Perforated panel

Water

Over flow pipe

Water outlet

To each temperaturemeasured point

Data logger

PCTemperature is kept at 20oC

Constant voltage device

Nonwoven fabric+ Perforated panel

Acrylic cylinder

Outlines of laboratory experiment

ΔH

Thermal probe


8/27


Cross section

Front view Side view Elevation view

Side view

Thermal probe

Temperature measurement point (Thermo couple)

Front view Elevation view

300

40

4050

5050

200

B

C

A

Acrylic cylinder

Water

Sand

Water

Used for comparison with calculated value, Point A, B, C

Water outlet


9/27


The experimental apparatus

Acrylic cylinder

Sand filled layer

Overflow pipe

Water outlet


10/27


Attachment of thermo couples

Temperature measurement point (Thermo couples)

Plastic mesh to set up thermo couples

Acrylic cylinder


11/27


Thermal probe

Temperature measurement point (Pt-100)

Heater Code

200

3.2

To Constant Voltage Device

To Data Logger

Heater

100

Stainless Steel Pipe

Composition

Photo


12/27


Experimental conditions

CASE1 CASE2 CASE3 CASE4 CASE5 CASE6Measured water flowrate [ml/min] 0 36 51 112 186 264

Water velocity throughthe sand layer [m/s] 0 8.39× 10-6 1.20× 10-5 2.64× 10-5 4.39× 10-5 6.22× 10-5

Water velocity throughthe sand layer [m/year] 0 265 377 833 1383 1963

•Atmosphere and supplied water temperature : 20 oC•Heating rate : 6.6W/m (1.32W)•Heating and measurement time : 10000 s(Only CASE1 is 1000 s)


13/27

Results of laboratory experiment

Temperature variation in the thermal probe according to elapsed time

0.00.51.01.52.02.53.03.54.04.55.0

10 100 1000 10000

t [s]

ΔT s

[ºC

] CASE1, CASE2, CASE3, CASE4, CASE5, CASE6 from top to bottom

Heating rate from thermal prove:6.6W/m

ΔTs：Temperature variation (Ts-Ts0) [oC], t：Elapsed time [m], λ: Thermal conductivity [W/m/K]q’’: Heating rate per length [W/m]

50 200 500

Approximated equation of Ts

( ) ltkTs += ln

Equation of effective thermal conductivity

( )kq

s πλ 4''=

b


14/27

Results of laboratory experiment

Variations of λs for each different period of the elapsed time

ugw : Ground water velocity

0

5

10

15

20

25

λ s [W

/m/K

]

1×10-5 2×10-5 3×10-5 4×10-5 5×10-5 6×10-5 7×10-5

0 500ugw [m/year]

1000 1500

0

ugw [m/s]

50s～100s100s～200s

200s～500s

500s～1000s

有効熱伝導率を推定するために使用した時間

1000s～5000s

5000s～10000s

Period of elapsed time

The effective thermal conductivities increase to infinity because of achievement the temperature to the steady state

If performance of the GSHP system in long term is evaluated by changing the effective thermal conductivity for the ground water flow, it is anticipated that error occurs

The thermal conductivities with the ground water flow are influenced by period of elapsed time


15/27

Method to calculate the thermal responses

Applying theoretical solution (The moving line source theory)

Ground water flow direction Infinite moving medium

Moving direction of medium

Line heat source with infinite length

y

xO

Moving velocity : u

φ

Line heat source with infinite length

Point Ar

Elevation viewSide view

( )( ){ }( ) '

'4'exp

'1

4'' 2

4

0

22

dttta

yttUxtt

qTr

tsa

sss ∫ ⎟⎟

⎠

⎞⎜⎜⎝

⎛−

+−−−

−=∆

πλββ

ββϕ

πλd

arU

aUrqT

r

tsa

ssss ∫ ⎟⎟

⎠

⎞⎜⎜⎝

⎛−−⎟⎟

⎠

⎞⎜⎜⎝

⎛=∆

24

02

22

161exp1cos

2exp

4''

The ground temperature at the certain point A is calculated by the following equation

a : Thermal diffusivity [m2/s], r : radius [m], U : Revised ground water velocity (=ucwρw / csρs), φ : radian angle, cwρw , csρs : Heat capacity of water and soil [kJ/m3]

(Diao et al. 2005)

16/27

Numerical calculation (The finite differential method)

200r

p200rp200rp

yx

Orp

A A

B

B B

B C

Area of numerical calculation

u∞ u∞

Calculated area and boundary conditions

Boundary conditions

A at y = 200rpTs=const

B , at x = 0 or x = 200rp

C at

y = -200rp

,

at

Partial differential equation

( ) 0=∇∇ hK

( ){ }xyxru p222 /1 ++= ∞φ

( ) ( )( )φρλρ ∇∇+∇∇=∂∂

TcTtTc swwss

sss

rp : radius of the cylindrical heat source [m]q : Heat flux [W/m2]λs : Thermal conductivity [W/m/K]φ : Velocity potential [m2/s] K : Hydraulic conductivity [m/h]

Method to calculate the thermal responses


17/27

Conditions

Comparison of thermal responses

B

C

A

Compared point•Effective thermal conductivity of saturated soil (by only conduction) : 1.85 W/m/K•Heat capacity of saturated soil : 2869 kJ/m3/K•Heating rate : 6.6 W/m

*Effective thermal conductivity is estimated with the temperature measured in CASE1

*Heat capacity is evaluated by giving the density of the particle of the sand of 2533 kg/m3, porosity of the soil of 36.7 %, and specific heat of the particle of the soil of 0.84 kJ/kg/K


18/27

Results of the comparison

In CASE2 (ugw= 265 m/year)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 2000 4000 6000 8000 10000

t [s]

ΔT s

[o C]

Measured

Theoretical solutionA

B

C

Numerical calculation


19/27

In CASE5 (ugw= 1383 m/year)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 2000 4000 6000 8000 10000

t [s]

ΔT s

[o C]

A

B

C

Measured

Theoretical solution


Results of the comparison


20/27

Applying the moving line source theory

From the laboratory experiment, the variation of the thermal response with ground water advection isn’t constant according to logarithm elapsed time

It is expected that the ground water velocity can be estimated by investigating gradient of the thermal responseThe gradient of the temperature kwf is expressed by the following equation

( ) ( ) ( )( ){ }tdtt

tTdttTtk sswf +

−+=

ln

New method to estimate the ground water velocity

k：Gradient of temperature [K], wf ：with ground water flow

Here, Ts in the above equation can be calculated by the moving line heat source theory.


21/27

Additionally, gradient of the non-dimensional temperature kwf* and non-

dimensional time Fo are introduced.

0.001

0.01

0.1

1

0 5 10 15 20

F o

k wf* R*=1.0 R*=0.005、0.01、

0.02、0.1、0.2

3

Approximated equation of kwf*

in range of Fo=3~20 kwf* = 0.5e

-Fo/4

0.001

0.01

0.1

1

0 5 10 15 20

F o

k wf* R*=1.0 R*=0.005、0.01、

0.02、0.1、0.2

3

Approximated equation of kwf*

in range of Fo=3~20 kwf* = 0.5e

-Fo/4kwf* = 0.5e

-Fo/4

Variations of kwf* according to Fo


kwf* = 0.5e

-Fo/4

Fo：Non-dimensional time [-](=U2t/as), k*：Gradient of non-dimensional temperature [-]wof ：Without ground water flow


22/27

Providing dimension to the approximate equation, gradient of temperature kwf is obtained by the following equation,

Here, constant number n is introduced

The number n can be provided by the exponential approximate equation of kwfaccording to t. The gradient of temperature kwf (t) can be calculated with a temperature variation measured in the actual experiment. The gradient of temperature without ground water advection kwf is obtained from the temperature variation in the short range of elapsed time.

satU

wofwf ekk 4

2−

≅

saUn4

2

=

ww

sss c

cnauρρ

×= 2

Then the ground water velocity can be calculated by using the constant number n.

The ground water velocity can be estimated with a thermal probe



23/27


Required time for the measurement

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 0.2 0.4 0.6 0.8 1

R *

F o

0

20

40

60

80

100

120

140

t [s

]

2.5×10-40 2.0×10-41.5×10-42.5×10-55.0×10-5

u [m/s]

Fo

t

Condition for calculation of tR = 1.6×10-3 m, λs = 1.85 W/m/K, csρs =2869 KJ/m3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 0.2 0.4 0.6 0.8 1

R *

F o

0

20

40

60

80

100

120

140

t [s

]

2.5×10-40 2.0×10-41.5×10-42.5×10-55.0×10-5

u [m/s]

Fo

t

Condition for calculation of tR = 1.6×10-3 m, λs = 1.85 W/m/K, csρs =2869 KJ/m3

Fo according to R* and the actual time t according to u in which relative error between kwof

* of calculation and approximation

If t ≥ 100 s, the measured data is available to estimate the ground water velocity

Equation of kwof*

Approximate equation of kwof

*

kwf* = 0.5e

-Fo/4

( ) ( ) ( )( ){ }***

*******

ln tdtttTdttTtk ss

wf+

−+=

ϕβϕβ

ββπ

π

ddRR

Tt

pps ∫ ∫ ⎟

⎟⎠

⎞⎜⎜⎝

⎛+−−=

0

*4

0

*2** cos

2161exp

211

Here,


24/27

Variations of gradient of temperatures according to the elapsed time

0.01

0.1

1

0 1000 2000 3000 4000

t [s]

k wf

CASE2: kwf = 0.283e-5.89×10-5tCASE2: kwf = 0.283e-5.89×10-5t




CASE6: kwf= 0.283e-3.57×10-3tCASE6: kwf= 0.283e-3.57×10-3t

Examples of estimation of ground water velocity

*The data measured in the laboratory experiment shown previously are used

=

n

=

n

=n=

n

=

n


25/27

Examples of estimation of ground water velocity

Comparisons of the ground water velocities between the estimation and the measurement

CASE2 CASE3 CASE4 CASE5 CASE6Measured watervelocity [m/s] 8.39× 10-6 1.20× 10-5 2.64× 10-5 4.39× 10-5 6.22× 10-5

Range of time forestimation [s] 500 ~ 4000 400 ~ 3000 300 ~ 2000 150 ~ 1000 130 ~ 700

n in Figure 10 5.89× 10-5 1.78× 10-4 8.16× 10-4 1.93× 10-3 3.57× 10-3

Estimated watervelocity [m/s] 8.45× 10-6 1.40× 10-5 3.14× 10-5 4.83× 10-5 6.57× 10-5

Relative error [%] 0.7 17.0 19.1 10.2 5.7

in previous graph

This method is effective to estimate the ground water velocity

Issues of this method1) Improvement of the accuracy of the temperature measurement2) Strengthening of the probe to be buried into the ground for measurement


26/27

Summary

1. From the laboratory experiments, it is indicated that the effective thermal conductivity with the ground water flow are influenced by period of elapsed time.

2. Applying the theoretical calculation and numerical calculation is effective for calculation of the ground temperature with the ground water flow because of good agreement between the calculated temperatures and the ones measured in the experiments.

3. A new method to estimate the ground water velocity was proposed. Then the examples indicated that the method is effective to estimate the ground water velocity.

Laboratory experiments with a thermal probe were carried out. As the result, the followings are obtained


27/27

Thank you for your attention !!

29/69

Additions

Development of calculation algorithm of ground temperature with ground water flow

30/72

Theoretical calculation (The moving line source theory)

Advantages and disadvantages of the methods

•Calculation speed is fast

•Advantage •Disadvantage

•Error with actual ground exchanger is occurred


•Unallowable time to calculate the ground temperature is required

•Thermal response surrounding a ground heat exchanger is reproducedmore accurately

Calculation algorithm of the thermal response is investigated based on results of theoretical calculation and the numerical calculation

T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland

31/72Development of calculation algorithm of ground temperature with ground water flow

For a single ground heat exchanger

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50

F o

T s*

For cylindrical heat source (Numerical calculation)

For line heat source (Theoretical calculation)

Rp*=0.4

Rp*=1.6Rp

*=6.4

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50

F o

T s*

For cylindrical heat source (Numerical calculation)

For line heat source (Theoretical calculation)

Rp*=0.4

Rp*=1.6Rp

*=6.4

Non-dimensional thermal response according to non-dimensional time Fo

Fo : Non-dimensional time (= U2t / a) [-], Rp* : Non-dimensional number (= Urp / a) [-],

Ts* : Non-dimensional temperature (= 2πλsΔTs / rp / q’’) [-]

Go to next page

When non-dimensional numbers RP* are the same, thermal responses on the surface of a cylindrical heatsource TS

* are the same



The thermal response is evaluated by multiplying a modification coefficient to the thermal response without the ground water flow

*

*

Cs

CswfC T

TC−

−=

The modification coefficient is calculated by the following equation

Modification coefficient CC according to non-dimensional time Fo

Tswf-C* : Non-dimensional temperature with ground water flow (by numerical calculation) [-]

Ts-C* : Non-dimensional temperature without ground water flow [-]

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50

F o

C

Rp*= 10.0, 6.4, 0.4, 3.2, 0.8, 1.6 from top to bottom

Approximate equation of CC according to Fo is given in the actual calculation



For multiple ground heat exchangers

1 2 j

A certain heat exchanger i

rdijrdi2rdi1 ･･･

rp

Ground water flow

φ

1 2 j

A certain heat exchanger i

rdijrdi2rdi1 ･･･

rp

Ground water flow

φ

The thermal response on the surface of a ground heat exchanger is obtained bysumming up the all thermal responses

Multiple ground heat exchangers buried in random layout

The thermal response of a certain ground heat exchanger i is calculated by the following equation

( ) ),(),(,1

trTtrTtrT pCswf

n

jdijCswfpsi −

=− ∆+∑∆=∆

( ) ( ) ( ) ( )∑

∂×∂

−=∆=

−−

*

0* *

******** ,1

,1t

CCsCwfs

CTtqtT

τ τττ

τ ( ) ( )( )( )∑∂

∂−+∑∆≅∆

=

=−

= =−=−

*

''** 2**

2**

0

*

***

1

****,1

,t

t

rRLswfn

iCkswfCswf r

CCCrTtqTtrT

τ

ϕϕ

ϕϕϕϕ τ

ττ

are obtained basis on these following equations( )tT Cwfs ,1−∆ ( )trT Cswf ,ϕϕ=−∆and

The thermal response in the ground with the ground water flow can be calculatedt* : Fourier number (= at / rp

2) [-], q* : Non-dimensional heat flux (= q / q0) [-], q0 : Unit heat flux (=1) [W/m2], CR, Cr , Cφ : Modification coefficient obtained by comparison between thermal responses for line heat source and cylindrical heat source

Comparison to numerical calculation 34/30


200r

p

200rp200rp rd

y

x

Orp

A A

C BB

B

B C

Area of numerical calculation

u∞ u∞

A Ts=const (u∞≠ 0) at y = 200rp + rp / 2

Boundary conditions

y = -200rp - rp / 2

B,

at

C

at

or

,

at

Calculated conditions

Non-dimensional temperatures calculated by the developed method and numerical method are compared.Rp

* is varied 0.1, 0.4, and 1.6. R* (= rd / rp) is set at 40.


Result of comparison 35/30

Comparison of non-dimensional thermal response

0.00.51.01.52.02.53.03.54.04.5

0 200 400 600 800 1000

t *

T s*

Developedmethod

Numericalcalculation

Rp* = 0.1 Downstream side

Rp* = 0.1 Upstream side Rp

* = 0.4 Downstream side

Rp* = 0.4 Upstream sideRp


Rp* = 1.6 Upstream side

0.00.51.01.52.02.53.03.54.04.5

0 200 400 600 800 1000

t *

T s*

Developedmethod

Numericalcalculation

Rp* = 0.1 Downstream side

Rp* = 0.1 Upstream side Rp


Rp* = 0.4 Upstream sideRp


Rp* = 1.6 Upstream side

Downstream side

Upstream side

Flowdirection


Examination of effect of the ground water flow to the GSHP system - Application of design tool 1-

Heat loss coefficient：1.57 W/m2/K

Room conditionHeating periodTemperature: 20oCCooling period Temperature: 26oCHumidity: 50%

Floor area: 130m2

Location : Sapporo, Japan

Cooling period: Jun. 9th - Sep.25thHeating period: Sep.26th - Jun. 8th

Heating load: 39.9 GJ Cooling load: 2.9 GJ

Calculated subject

To the ground heat exchangers

Heating system :Floor heating 50m2 + Fan-convector×3(Heating capacity 1.6kWat 55oC- 20oC)

Heat pump unitCompressor :2 - Horse powerCOP(0-35℃)：4.5

Brine: Organic acid group 40%

Circulation pump (Built-in type)Primary side:100W Secondary side:50W(During cooling period only primary side operated)

Cooling system :Fan-convector×3(Heating capacity 1.1kWat 7oC- 26oC)


36/72

Effect of the ground water flow to the GSHP system

Calculated conditions

•Effective thermal conductivity: 1.5 W/m/K•Heat capacity: 3000 kJ/m3/K•Ground temperature: 10.4 oC•Ground water temperature: 10.4 oC (= Ground temperature)

CASE1: A single ground heat exchanger is used

CASE2: Multiple ground heat exchangers with length of 10 m are used

•Average COP and SCOP during heating period according to ground water velocity when the length is 100 m constant

•Required number of the ground heat exchanger and the total length

•The length on a condition that average COP during heating period is the same as the one of ugw = 0

•Cost payback time and life cycle cost in these cases

Soil properties

Calculate

Calculate

*Ground water velocity is the same in all geological layer

ugw


37/72

Results

Average COP and SCOP during heating period according to ground water velocity

3.0

3.5

4.0

4.5

5.0

5.5

6.0

0 200 400 600 800 1000

u gw [m/year]

CO

P 、SC

OP

COP SCOP

Length of the ground heat exchanger = 100 m


38/72

Results

Length of the ground heat exchanger and initial cost of the GSHP system

0

20

40

60

80

100

120

0 200 400 600 800 1000

u gw [m/year]

Leng

th o

f gro

und

heat

exch

ange

r [m

]

1.8

2.0

2.2

2.4

2.6

2.8

3.0

Initi

al c

ost [

106

yen]

Length Initial cost

100

58 m

2.7 × 105 JPY

*110 JPY = 1 USD

JPY

Average COP during heating period = 4.6

140 JPY = 1 EUR


39/72

Results

Cost payback time and life cycle cost *Conventional system : Oil boiler and air conditioning system

Seizing the ground water velocity and designing the GSHP system with shorter length are more effective on reflecting the ground water flow effect

0

2

4

6

8

10

12

0 200 400 600 800 1000

u gw [m/year]

Cos

t pay

back

tim

e [y

ear]

100

105

110

115

120

125

130

Life

cyc

le c

ost [

103 ye

n/ye

ar]

Length is 100 m constant

Length is varied on a condition of the average COP=4.6

JPY


40/72

Results

Number and total length of the ground heat exchangers with length of 10 m

0

5

10

15

20

25

0 200 400 600 800 1000

u gw [m/year]

Num

ber

0

50

100

150

200

250

Tota

l len

gth

[m]

100

Total length is almost the same as the one of a single ground heat exchanger

Using multiple ground heat exchangers with short length is more effective, if there are ground water flow with large velocity in shallow geological layer

60 m


41/72

An example of urban exhaust heatLocation : Downtown of Sapporo city

Sapporo (Capital of

Hokkaido island)

Tokyo

Osaka Japan


1 km2

Sapporo central railway station

Amount of exhaust heat from black water : Approx. 40 TJ /year

Map of downtown of Sapporo city

(Narita et al. 1996)

Feasibility study of low energy system utilizing urban exhaust heat - Application of design tool 2-

42/72

Feasibility study

Outlines of the low energy system utilizing urban exhaust heat with the ground water for thermal transport

1. Sewage-disposal plant is constructed at the center of the city.

2. Exhaust heat from black water is injected into the ground.

3. The heat is extracted with ground heat exchangers buried in the ground of downstream of the ground water flow. The extracted heat is used as heat source of such as heat pumps.

Flow of sewage-disposal system


ScreenFlow

Equalization Tank

Flow Equalization

Tank

Biological Treatment

TankSettling

Tank

Membrane Filtration Equipment

Disinfections Tank

DisposalTank

Black Water

Inject exhaust heat into the ground by cultivating the water

Inject exhaust heat into the ground with ground heat exchangers

Inject exhaust heat into the ground with ground heat exchangers

43/72

Schematic diagram Side view

Flow Equalization TankHeat Pump (8 horse power)

Borehole Heat Exchangers (The length is 50m)

Heat Injection

Side

Heat Extraction

Side

5m 5m 5m 5m 5m 5m20m

Disposal Plant Calculated Area

3m3m

Ground Water Flow : 100 m/year

50 m

Heat Exchanger

T2out = 40 oC

Plane view


Feasibility study 44/72

Feasibility study

Calculated conditionsSapporo

11.01.5

15002.0100

External diameter of U-tube [m] 0.032Diameter of borehole [m] 0.12

Borehole thermal conductivity[W/m/K] 1.8

8 house-power404.0

Heat extraction side 150W,Heat injection side50W

CityGround temeperature [℃]

Effective thermal conductivity [W/m/K]Density [kg/m3]

Ground water velocity [m/year]

Circulation pump

Outlet temperature in secondary side [℃]

Specific heat [kJ/kg/K]

Ground heatexcahgner

SingleU-tube

Heat pumpCompressor

COP (0℃－35℃)

Soil property

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecTemperature in the flowequalization tank [oC] 13.6 13.2 11.1 13.1 15.1 18.8 20.8 21.6 21.1 19.1 16.4 14.6


(Narita et al. 1996)

45/72

Results

0

50

100

150

200

250

0 1 2 30

2

4

6

8

10

Number of borehole heat exchangers of heat injection side

Am

ount

of e

xtra

cted

or

inje

cted

hea

t [G

J]

Hea

t rec

over

y ra

te [%

]

Amount of extracted heat

Amount of injected heat

Heat recovery rate (=Increase of extracted heat – Injected heat)

0

50

100

150

200

250

0 1 2 30

2

4

6

8

10

Number of borehole heat exchangers of heat injection side

Am

ount

of e

xtra

cted

or

inje

cted

hea

t [G

J]

Hea

t rec

over

y ra

te [%

]

Amount of extracted heat

Amount of injected heat

Heat recovery rate (=Increase of extracted heat – Injected heat)

Heat recovery rate for number of borehole ground heat exchangers


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Results

Comparison of CO2 emissions with conventional systems

0

5

10

15

20

25

30

GSHP Oil boiler Gas boiler

CO

2 em

issi

ons [

t]


Condition of the comparison:Each system produces heat as much as the one produced by the GSHP system

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HEAT TRANSFER EXPERIMENT IN THE GROUND WITH … · HEAT TRANSFER EXPERIMENT IN THE GROUND WITH ......

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