Title: CRAFT project PLAXIS developments 2002-2004
1NEW 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
2Objectives
- Development
- of
- Computationally EFFICIENT 3D Finite Element
- Tools
- for
- Geothermal Analysis and Heat Pipe Design
3Heat Flow in GeothermalHeating Systems
4Challenges in GeothermalHeating Systems
Extreme disproportionate geometries !!
Slenderness ratio 1/5000
5Limitations of Current Techniques
- Analytical Techniques Too many simplifications
- Finite Difference Technique Limited in
geometrical simulation - Finite Element Technique Computationally
extremely expensive
6Current Techniques
Top View
Finite Element Method
3D Finite Element Mesh
10 m
10 m
10 m
Aspect Ratio
Element no. 4466
7Current 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
8New 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!
9Numerical 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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12Output Results
Temperature distribution
13GWF 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
1430 min.
60 min.
15Model Validation
Comparison with Measurements
16Measured Data
Field test at Leutkirch
17Numerical 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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19Measured vs. Calculated
20More Examples
Multiple layers and pipes
21More Examples
GWF Effect
22More Examples
Air Temperature Effect
23Conclusions
- 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.