Coupling Subsurface and Above-Surface Models for Optimizing the Design of Borefields and District Heating and Cooling Systems

Description

Accurate dynamic energy simulation is important for the design and sizing of district heating and cooling systems with geothermal heat exchange for seasonal energy storage. Current modeling approaches in building and district energy simulation tools typically consider heat conduction through the ground between boreholes without flowing groundwater. While detailed simulation tools for subsurface heat and mass transfer exist, these fall short in simulating above-surface energy systems. To support the design and operation of such systems, the study developed a coupled model including a software package for building and district energy simulation, and software for detailed heat and mass transfer in the subsurface. For the first, it uses the open-source Modelica Buildings Library, which includes dynamic simulation models for building and district energy and control systems. For the heat and mass transfer in the soil, it uses the TOUGH simulator. The TOUGH family of codes can model heat and multi-phase, multi-component mass transport for a variety of fluid systems, as well as chemical reactions, in fractured porous media. The study validated the coupled modeling approach by comparing the simulation results with one from the g-function based ground response model. It then looked into effects when the water table and the regional groundwater flow are considered in the ground, from the perspective of heat exchange between borehole and ground, and the electrical consumption of the district heating and cooling systems. To access the simulation models, please find the links in the submission: -- For coupled approach validation: see model Buildings.Fluid.Geothermal.Borefields.Examples.BorefieldsWithTough and Buildings.Examples.DistrictReservoirNetworks.Examples.Reservoir3Variable_TOUGH from the "Modelica Building Library" resource, branch issue1495_tough_interface, commit a2667c0. -- For the study of the effect of water table: see model Buildings.Examples.DistrictReservoirNetworks.Examples.Reservoir3Variable_TOUGH from he "Modelica Building Library" resource, branch issue1495_tough_interface_moreIO, commit 760de49. -- For the study of the effect of regional groundwater flow: see Buildings.Examples.DistrictReservoirNetworks.Examples.Reservoir3Variable_TOUGH from he "Modelica Building Library" resource, branch issue1495_tough_interface_moreIO_3D, commit c2a2d2a. The coupling interface script "GrounResponse.py" can be found from the above links in the folder Buildings/Resources/Python-Sources. Also, the needed files for TOUGH simulation are in the folder Buildings/Resources/Python-Sources/ToughFiles that can be accessed through the above links. A brief description of these files is given below; detailed specifications for the first three files may be found in the TOUGH3 Users Guide (Jung et al., 2018) https://tough.lbl.gov/documentation/tough-manuals/. (1) INCON - initial conditions for each grid block (2) INFILE - main input file with material properties and control parameters (3) MESH - description of the computational grid (4) readsave - Modelica/TOUGH interface program: read the final output of TOUGH simulation after TOUGH time step and prepare for transfer to Modelica for next Modelica time step (5) readsave.inp - input parameters for program readsave (6) writeincon - Modelica/TOUGH interface program: write the output of Modelica after Modelica time step and prepare for transfer to TOUGH as initial conditions for the next TOUGH step (7) writeincon.inp - input parameters for program writeincon

Resources

Name Format Description Link
0 The model was created with the modules in the Modelica Buildings Library. When running the model, it will call the TOUGH simulation every 30 minutes. The coupling between Modelica and TOUGH is through the script "GroundResponse.py" in folder Buildings/Resources/Python-Sources. It will call the TOUGH simulator which is installed at /opt/esd-tough/tough3-serial/tough3-install/. The required files for TOUGH simulation are in folder Buildings/Resources/Python-Sources/ToughFiles . https://github.com/lbl-srg/modelica-buildings/blob/issue1495_tough_interface/Buildings/Examples/DistrictReservoirNetworks/Examples/Reservoir3Variable_TOUGH.mo
0 Different from the model used for validating the coupling approach, this model considered the water table in the ground. It was implemented by settings in the INFILE and the INCON for TOUGH simulation. Please see the attached paper "Doughty2021_waterTableEffect.pdf" and "Hu2022_waterFlowEffect.pdf". https://github.com/lbl-srg/modelica-buildings/blob/issue1495_tough_interface_moreIO/Buildings/Examples/DistrictReservoirNetworks/Examples/Reservoir3Variable_TOUGH.mo
0 This model considered the regional water flow in the ground. It studied how the flow affects the heat exchange between borehole and the ground, and those affect the overall performance of the above-ground energy system. See paper "Hu2022_waterFlowEffect.pdf" for detailed information. https://github.com/lbl-srg/modelica-buildings/blob/issue1495_tough_interface_moreIO_3D/Buildings/Examples/DistrictReservoirNetworks/Examples/Reservoir3Variable_TOUGH.mo
57 Coupled simulation results for validating the coupling approach. It compared the pure-conduction TOUGH simulation with the g-function-based approach. https://gdr.openei.org/files/1365/01-Validation.zip
57 The package includes the simulation results for investing the regional groundwater flow's effect on the heat transfer between the ground and the borehole. It looked into the effect on electrical consumption and also looked into the long-term performance of the system. https://gdr.openei.org/files/1365/03-Ground-waterflow.zip
57 The package includes the simulation results for investing the water table effects on the heat transfer between borehole and ground. It looked into the different permeabilities and the bottom pressure profiles. https://gdr.openei.org/files/1365/02-Water-Table_effect.zip
33 It's the paper presenting the effects of the groundwater flow on the performance of the district energy system. https://gdr.openei.org/files/1365/Hu2022_waterFlowEffect.pdf
33 It's the paper presenting the effects of the water table on the heat exchange between the ground the borehole. However, it includes only purely TOUGH simulation results. https://gdr.openei.org/files/1365/Doughty2021_waterTableEffect.pdf
33 A paper that has a detailed introduction of how the Modelica and TOUGH are coupled. It also validated the coupling approach by comparing the simulation results with the g-function-based simulation results. https://gdr.openei.org/files/1365/Hu2020_validation.pdf
21 The Modelica Buildings library is a free open-source library with dynamic simulation models for building energy and control systems. https://github.com/lbl-srg/modelica-buildings

Tags

  • seasonal-energy-storage
  • district-heating
  • district-energy-system
  • coupling
  • modeling
  • geothermal-heat-exchange
  • optimization
  • borefield
  • energy-storage
  • modelica
  • python
  • modelica-buildings-library
  • geothermal-bofield
  • code
  • model
  • ground-source-heat-pump
  • tough
  • simulation
  • district-cooling
  • geothermal
  • gshp
  • energy

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