In urban areas with limited space, deep borehole heat exchangers (DBHE) are coupled with ground source heat pump systems (GSHPS) to extract geothermal energy for building heating purposes. They can exploit more heat than common shallow systems. In this thesis, the open source software OpenGeoSys (OGS) has been utilized to analyse the long-term behavior and temperature evolution in and around single and multiple DBHEs. Moreover, an analysis to reduce the computation time has been applied. This way, the simulation time could be shortened by almost 75% by adjusting the tolerance of the non-linear solver and using an automatic time stepping in a first step. With larger element sizes, which still provide a sufficient result precision, the required duration could be shortened to less than 2% compared to the first method. Especially between the top and the bottom a layer size of 100 m is sufficient. The thickness around the top and bottom, however, should be small to avoid numerical inaccuracies. In the first years of operation most of the energy is extracted by the lower parts of the DBHE. Throughout the years, the contribution along the depth becomes more homogeneous and more soil is influenced. In summer, the top approximately 900 m are not contributing to the heat extraction but instead losing heat to the soil because of a low energy demand, which leads to high inflow temperatures. Considering the results of the in- and outflow temperature evolution, a single DBHE should be preferred over multiple systems. Nonetheless, those can multiply the extractable heat in a certain area and could be more economical.:List of Figures . . . v
List of Tables . . . vii
1 Introduction . . . 1
2 Theoretical Background . . . 4
2.1 BHE equations . . . 5
2.2 Thermal Resistance . . . 6
2.3 Exchange Area . . . 10
2.4 Coefficient of Performance . . . 10
2.5 OpenGeoSys Pipe Network Feature . . . 12
3 Modeling Scenarios . . . 14
3.1 Model Setups . . . 15
3.2 Model Verification . . . 16
3.3 Model Environment . . . 20
3.4 Initial and Boundary Conditions . . . 22
3.5 Investigation on Computation Time Influences . . . 24
4 Results and Discussion . . . 30
4.1 In- and Outflow Temperature Evolution . . . 30
4.2 Energy Distribution . . . 34
4.3 Soil Heat Flux . . . 40
4.3.1 Winter in 2nd year . . . 41
4.3.2 Summer in 2nd year . . . 44
4.3.3 Winter in 30th year . . . 47
4.3.4 Summer in 30th year . . . 49
4.4 DBHE Heat Flux . . . 51
4.5 Soil Heat Flux in the Multiple DBHE Case . . . 55
4.5.1 Line Setup . . . 56
4.5.2 Square Setup . . . 61
4.6 Numerical Inaccuracies . . . 65
5 Conclusion . . . 68
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:73812 |
| Date | 11 February 2021 |
| Creators | Randow, Jakob |
| Contributors | Hochschule für Technik, Wirtschaft und Kultur |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:masterThesis, info:eu-repo/semantics/masterThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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