Fabian Ochs - Stockton University · Fabian Ochs 28 summary + conclusion • thermal insulation...

Fabian Ochs 1

ITW – University of Stuttgart

Institute of Thermodynamics and Thermal Engineering (ITW)Professor Dr. Dr.-Ing. H. Müller-Steinhagen

University of StuttgartPfaffenwaldring 6, 70569 Stuttgart

Tel.: 0049 711 685 6 3278, Fax: 00 49 711 685 6 3242email: [email protected], internet: www.itw.uni-stuttgart.de

EFFECTIVE THERMAL CONDUCTIVITY OF THE INSULATION OF HIGH TEMPERATURE

THERMAL UNDERGROUND STORES DURING OPERATION

Fabian Ochs

supported by

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outline

• introductionsolar assisted district heating with seasonal heat storepilot projects with buried heat store

• thermal conductivity of insulation• outdoor experiments

construction of the research storesmeasurement of the thermal conductivity of the insulation during operation

• conclusion

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application of large heat stores

• district heating (peak shaving)• heat and power cogeneration• process heat• solar assisted district heating

Brennwert-KesselGas

HeizzentraleFlachkollektoren

Wärmenetz

SolarnetzSaisonalerWärmespeicher

Wärmeüber-gabestation

heating centralsolar collector

seasonal heat store

solar net

heat transfer subsystem

heat distribution net

Hannover, 2000

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concepts of seasonal heat stores

Kies/Wasser-Wärmespeicher

Erdsonden-Wärmespeicher

Heißwasser-Wärmespeicher

Sommer Winter

WärmedämmungAbdichtungSchutzvlies

aquifer thermal energy store (ATES)

60 to 80 kWh/m³40 to 50 kWh/m³

15 to 20 kWh/m³30 to 40 kWh/m³

hot water tank store (HWTS) gravel water pit heat store (GWHS)

borehole thermal energy store (BTES)

linerinsulationfleece

thermal insulation

cover wall bottom

HWTS yes yes should

GWHS yes should should

BTES yes no no

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experiences from pilot projects

PKi • Pfeil & Koch ingenieure

Stuttgart, 1983

more than 10 pilot and research projects successfully realized in Germany between 1983 and 2006

Quelle: ZSWQuelle: ZSWChemnitz, 1997 Steinfurt, 1999

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PKi • Pfeil & Koch ingenieure Quelle: ZSWQuelle: ZSWChemnitz, 1997 Steinfurt, 1999

Stuttgart, 1983

Volume[m]

Measurement[MWh/a] Qmeasured/Qdesign

tank heat stores

Friedrichshafen 12 000 320 – 360 1.5-1.6

Hamburg 4 500 360 – 430 3.8-4.5

Hannover 2 750 90 – 100 1.3-1-4

pit heat stores

Stuttgart 1 000 27 n/a

Chemnitz1) 8 000 n/a 1.4

Steinfurt2) 1 500 70 – 90 n/a


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• tank and pit heat stores are technical feasible

• technical details have to be optimized• thermal losses are too high• construction costs are still too high

⇒ optimization of the thermal insulation


Stuttgart, 1983

PKi • Pfeil & Koch ingenieure Quelle: ZSWQuelle: ZSWChemnitz, 1997 Steinfurt, 1999

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measurement of the thermal conductivity

rockwoolexpanded glass granules foamglass

measurement of the effective thermal conductivity

• guarded heating plate device according to DIN 52612• measurement of dry and moistened specimens• measurement in the relevant temperature range from

20 to 80 °C• modeling of the effective thermal conductivity as a

function of the water content and the temperature

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modeling of the thermal conductivity

rockwoolexpanded glass granules

20 40 60 800

0.2

0.4

0.6

0.8

1

T / [°C]

λ eff /

[W/(m

K)]

u/ufs = 0.00

u/ufs = 0.09

u/ufs = 0.16

u/ufs = 0.30

u/ufs = 0.49

measurement model prediction

foamglass

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modeling of the thermal conductivity

rockwoolexpanded glass granules

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

u/ufs / [-]

λ eff /

[W/(m

K)]

95 °C

85 °C

75 °C

65 °C

5 °C

35 °C

45 °C

foamglass

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outdoor laboratories

laboratory 1laboratory 2

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outdoor experiments – installation of liner

or shotcrete layer

water

liner

protective fleece

soil

insulationdrainage grid

vapour barrier

vapour retarder

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outdoor experiments – pneumatic injection of the insulation

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water

liner

protective fleece

soil

insulationdrainage grid

vapour barrier

vapour retarder

heat flux sensor

temperature sensor

0.5 m

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effective thermal conductivity

ϑ∆∆⋅

=ϑλ

⋅

xq)u,( m Fourier‘s Law

2ch

mϑ+ϑ

=ϑ

cϑhϑ

heat flux sensor

temperature sensor

∆x

⋅

q

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vapour barrier liner

installation of direct charging system, connected to• district heating + 170 kW gas boiler• district cooling system of the university

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calculation methods for the thermal conductivity

• checking the results by comparing results ofi. measurement with heat flux and temperature sensorsii. calculation by balancing one layer of the storeiii. calculation by balancing the entire store

• comparison with modeled results, validated with data that have been obtained by indoor measurements

ϑn+1

ϑn

ϑn-1

Qn,n+1

Qn,n-1

ϑa hn+1

hn-1

ln

Qv

dmean

n+1

n

n-1

v1n,n1n,n QQQdtdU

++= −+

dtdTmc

dtdU

v ⋅=

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measurement during operation

W1

W2

W3

W4B

location of the heat flux sensorsoutdoor laboratory 2

outdoor laboratory 1

W1

W2W3

W4Clocation name slope measured

cover C -

80°

60°

80°

80°

-

yes

west wall W1 yes

south wall W4 yes

north wall W2 yes

east wall W3 no

bottom B yes

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results - comparison of the methods

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0 200 400 600 800 1000 1200 1400

t / [h]

λ eff

/ [W

/(m K

)]

10

15

20

25

30

35

40

45

50

55

60

∆T

/ [°C

]

λeff W2

λeff W4

λeff,av,layer0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0 200 400 600 800 1000

t / [h]

λ eff / [

W/(m

K)]

10

15

20

25

30

35

40

45

50

55

60

∆T

/ [K]λeff W2

λeff B

λeff W4

λeff C

λeff,av,tot

balancing the entire store:

charging at constantstorage temperature

balancing one layer of the store:

decreasing storage temperature without(dis-)charging

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measured thermal conductivity during operation

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thermal conductivity as a function of temperature

0.00

0.05

0.10

0.15

0.20

0.25

0.30

10 20 30 40 50 60

T / [°C]

λ eff

/ [W

/(m K

)]

L1 W1, measurement L1 W1, best (lin) fitL1 W2, measurement L1 W2, best (exp) fitL1 W4, measurement L1 W4, best (lin) fitL1 B, measurement L1 B, best (exp) fit

0.00

0.05

0.10

0.15

0.20

0.25

0.30

10 20 30 40 50 60

T / [°C]

λ eff

/ [W

/(m K

)]

L2 C, measurement L2 C, best (lin) fit L2 W2, measurement L2 W2, best (exp) fitL2 W4, measurement L2 W4, best (lin) fitL2 B, measurement L2 B, best (exp) fit

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state of the insulation after deconstruction

Deconstruction of the research store

• north wall and bottom insulation are (partially) wet

• moisture contents of 150kg/m³ and 380kg/m³, respectively

• good agreement between model and monitoring data

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comparison of modeled and measured data

research store andlocation

moisture content

(measured) model(based on laboratory measurement)

kg/m³ W/(m K)

20 °C 35 °C 50 °C

west wall (W1) 0 0.07 0.06 0.08 0.07 0.08 0.07

north wall (W2) 145 0.10 0.13 0.14 0.19 0.19 0.26

south wall (W4) 0 0.06 0.06 0.06 0.07 0.07 0.07

bottom (B) 383 0.13 0.19 0.21 0.26 NV 0.36

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summary + conclusion

• thermal insulation must remain dry• wall construction must be water and water vapour proof

towards the inside and water proof but open for vapourdiffusion towards the surrounding ground

• design and construction of the wall assembly require dynamic simulation of the coupled heat and moisture transport

• knowledge about the thermal conductivity of the insulation (as a function of temperature and moisture content) and about the vapour diffusion resistance index of the liner is therefore required

• good agreement between different calculation methods and model

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Thank you for your attention!

Fabian Ochs - Stockton University · Fabian Ochs 28 summary + conclusion • thermal insulation...

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