CRAFT project PLAXIS developments 2002-2004

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NEW AND CLASSICAL APPLICATIONS OF HEAT FLOW
STUDIES Aachen (Germany), October 4-7, 2004
Efficient 3D Finite Element Analysis for
Geothermal Heating and Cooling Systems
Rafid al Khoury PLAXIS bv / Delft University of
Technology
Dirk Leyens EnBW Energie Baden-Württemberg AG
Thomas Kölbel Birkenfeld Ralf Schramedei Stadtwer
ke Düsseldorf

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Objectives

• Development
• of
• Computationally EFFICIENT 3D Finite Element
• Tools
• for
• Geothermal Analysis and Heat Pipe Design

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Heat Flow in GeothermalHeating Systems

• Conduction Convection

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Challenges in GeothermalHeating Systems
Extreme disproportionate geometries !!
Slenderness ratio 1/5000
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Limitations of Current Techniques

1. Analytical Techniques Too many simplifications
2. Finite Difference Technique Limited in
   geometrical simulation
3. Finite Element Technique Computationally
   extremely expensive

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Current Techniques
Top View
Finite Element Method
3D Finite Element Mesh
10 m
10 m
10 m
Aspect Ratio
Element no. 4466
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Current Techniques
Finite Element Method
using aspect ratio 5 leads, for 10 m depth
80 000 element 100 m depth 800 000
element 150 m depth 1 200 000 element
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New Approach
Criteria
A 3D model Heat pipe, Layered media,
Conduction, Convection, Groundwater Flow. A
computationally efficient tool3D finite element
tools that can be used for everyday engineering
practice.
Approach
Development of a New Finite Element for the heat
pipe Reduction of finite element mesh size from
hundred of thousands of elements to few hundreds!
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Numerical Example
Transient and Steady StateCalculations
Pipe Double U-shape Pipe length 100m Soil
150m x 150m x 100m T_in 5 ?C Initial
temperature in soil 20 ?C
Finite Element Mesh
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Output Results
Temperature distribution
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GWF Effect
Pipe Double U-shape Pipe length
100m T_in 5 ?C Initial
temperature in soil Left 30 ?C Right
20 ?C Initial GW heads in soil Left 150
m Right 148 m
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30 min.
60 min.
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Model Validation
Comparison with Measurements
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Measured Data
Field test at Leutkirch
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Numerical Simulation
Pipe Double U-shape Pipe length 100m Soil
40m x 150m x 40m T_in variable
Soil temp. profile
Finite Element Mesh
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Measured vs. Calculated
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More Examples
Multiple layers and pipes
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More Examples
GWF Effect
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More Examples
Air Temperature Effect
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Conclusions

• The model is capable to simulate transient and
  steady state conditions.
• Small mesh size is sufficient.
• The model is useful to
• Engineers improve their
  design.Researchers introduce new criteria for
  better design.Technologists improve the BHE
  system components.