heat transfer experiment in the ground with … · heat transfer experiment in the ground with ......
TRANSCRIPT
HEAT TRANSFER EXPERIMENT IN THE GROUND WITH
GROUND WATER ADVECTION
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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.
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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
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Outlines of laboratory experiment
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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Outlines of laboratory experiment
The experimental apparatus
Acrylic cylinder
Sand filled layer
Overflow pipe
Water outlet
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Outlines of laboratory experiment
Attachment of thermo couples
Temperature measurement point (Thermo couples)
Plastic mesh to set up thermo couples
Acrylic cylinder
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Outlines of laboratory experiment
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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Outlines of laboratory experiment
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)
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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)
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
Numerical calculation
Results of the comparison
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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.
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
New method to estimate the ground water velocity
kwf* = 0.5e
-Fo/4
Fo:Non-dimensional time [-](=U2t/as), k*:Gradient of non-dimensional temperature [-]wof :Without ground water flow
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
New method to estimate the ground water velocity
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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New method to estimate the ground water velocity
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,
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
CASE3: kwf = 0.283e-1.78×10-4tCASE3: kwf = 0.283e-1.78×10-4t
CASE4: kwf = 0.283e-8.16×10-4tCASE4: kwf = 0.283e-8.16×10-4t
CASE5: kwf = 0.283e-1.93×10-3tCASE5: kwf = 0.283e-1.93×10-3t
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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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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
T. Katsura, et al. IEAs 10th Energy Conservation Thermal Energy Storage Conference Ecostock’2006, New Jersey, USA, 2006. 6. 1
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Thank you for your attention !!
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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
Numerical calculation
•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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
32/72Development of calculation algorithm of ground temperature with ground water flow
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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
33/72Development of calculation algorithm of ground temperature with ground water flow
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
Numerical calculation
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.
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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
* = 1.6 Downstream side
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
* = 0.4 Downstream side
Rp* = 0.4 Upstream sideRp
* = 1.6 Downstream side
Rp* = 1.6 Upstream side
Downstream side
Upstream side
Flowdirection
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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)
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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An example of urban exhaust heatLocation : Downtown of Sapporo city
Sapporo (Capital of
Hokkaido island)
Tokyo
Osaka Japan
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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-
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
(Narita et al. 1996)
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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
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
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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]
T. Katsura, Lecture Series SIT, 2006-5-15, Yverdon-les-Bains, Switzerland
Condition of the comparison:Each system produces heat as much as the one produced by the GSHP system
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