Shallow Geothermal Systems: Recommendations on Design, Construction, Operation and Monitoring

The recommendations summarise the state of the art. Their aim is the proper exploitation of the ground for geothermal purposes without adversely affecting the ground or the groundwater on the one hand and the operation of the system and nearby buildings on the other. The recommendations should be used during consulting, design, installation and operation in order to achieve optimum and sustainable use of the ground at a specific location. Authorities responsible for supervising and approving projects can use the recommendations as a guide when taking decisions and making stipulations. The Geothermal Energy Study Group was set up in Bochum in 2004 and became the joint DGGV/DGGT study group in 2007. Some 20 specialists from universities, authorities and engineering consultants are active in the group and meet two or three times a year.

Table of Contents:
Preface  IX Acknowledgements  XIII List of Figures  XV List of Tables XXV Preamble XXVII Notation XXIX 1 Introduction  1 2 Principles  5 2.1 Geological, hydrogeological and geotechnical principles  5 2.2 Geothermal principles 12 2.3 Solar energy zone  29 2.4 Geosolar transition zone  31 2.5 Terrestrial zone  35 2.6 Anthropogenic thermal influence  36 2.7 Interaction between geothermal energy systems and the ground 37 2.7.1 Hydrochemical interactions  39 2.7.2 Interactions between geothermal systems and groundwater organisms 39 3 Geothermal energy installations  41 3.1 Closed systems  42 3.1.1 Borehole heat exchangers (downhole heat exchangers) 42 3.1.2 Heat pipes 50 3.1.3 Horizontal collectors 51 3.1.4 Thermal piles and concrete components in contact with the soil  55 3.2 Open systems (direct use of groundwater) 59 3.2.1 Well systems 61 3.2.2 Geothermal energy in conjunction with mines and underground workings 65 3.3 Geothermal energy storage concepts  70 3.3.1 Aquifer thermal energy storage  70 3.3.2 Borehole thermal energy storage  71 3.3.3 Cavern thermal energy storage (CTES) 72 4 Legislative principles  73 4.1 Water legislation 73 4.1.1 European regulations  73 4.1.2 National law 74 4.2 Mining legislation 74 4.3 Natural mineral deposits legislation  75 4.4 Nature and landscape conservation  75 4.4.1 The european ‘natura 2000’ ecological network  75 4.4.2 Nature and landscape conservation  76 4.5 Environmental impact assessment  77 4.6 Non-statutory regulations  77 5 Planning principles 78 5.1 Project workflow 79 5.1.1 Establishing the basis of the project  79 5.1.2 Preliminary design  80 5.1.3 Final design  80 5.1.4 Building permission application  81 5.1.5 Detailed design  81 5.1.6 Preparing for contract award and assisting in award process 82 5.1.7 Supervising and setting up the operation  82 5.2 Surveying requirements for BHE installations  83 5.2.1 Geothermal category 1 83 5.2.2 Exploratory measures for category 1 84 5.2.3 Geothermal category 2 84 5.2.4 Additional exploratory measures for category 2  84 5.2.5 Geothermal category 3 84 5.2.6 Additional exploratory measures for category 3  84 5.3 Models for simulating heat transfer 85 6 Boreholes and completion 91 6.1 Drilling methods 91 6.2 Equipment in boreholes 94 6.3 Boreholes: deviation from the vertical  97 6.4 Geological and hydrogeological influences 104 6.5 Response test methods 109 6.5.1 GRT concepts and measuring principle  110 6.5.2 Evaluation. 111 6.5.3 Thermal resistance of borehole 115 6.5.4 Quality control with the help of the GRT  117 6.5.5 Evaluation of unsteady GRT data  118 6.5.6 Cylinder source method 119 6.5.7 Enhanced geothermal response test  136 7 Design, construction and operation of closed systems  143 7.1 sBHE systems  143 7.1.1 Detailed design  143 7.1.2 Backfilling the annular space 155 7.1.3 Requirements profile for backfill material  158 7.1.4 BHEs that are not fully sealed 177 7.1.5 Pressure and flow tests for BHEs  179 7.1.6 Thermal transfer fluids 190 7.1.7 Horizontal connecting pipes and connection to building services  194 7.1.8 Commissioning, operation and maintenance 196 7.1.9 Documentation 199 7.1.10 Abandoning and decommissioning  200 7.2 Horizontal collectors 201 7.2.1 Planning and designing collector systems 201 7.2.2 Installation of horizontal collectors  205 7.2.3 Installation of geothermal energy baskets  205 7.2.4 Laying the pipes 206 7.2.5 Filling and bleeding 206 7.2.6 Thermal transfer fluids 207 7.2.7 Pressure tests 207 7.2.8 Commissioning 207 7.2.9 Documentation 207 7.2.10 Operation of horizontal collector 209 7.2.11 Effects of operating horizontal collectors 209 7.2.12 Abandoning and decommissioning  210 8 Design, construction and operation of open systems 211 8.1 Well systems 211 8.1.1 Detailed design 218 8.1.2 Site supervision, quality assurance, documentation  220 8.1.3 Pumping and well tests 220 8.1.4 Commissioning, operation and maintenance 220 8.1.5 Hydrochemical and microbiological influences 225 8.1.6 Documentation 230 8.1.7 Abandoning and decommissioning  230 8.1.8 Practical example of a well system  230 8.2 Aquifer thermal energy storage (ATES) 235 9 Risk potential 236 9.1 The 5-M method 236 9.1.1 Man 236 9.1.2 Method 237 9.1.3 Materials 238 9.1.4 Machines 239 9.1.5 Medium 239 9.1.6 Summary 240 9.2 Geological risks  241 9.2.1 Rocks with swelling or subsidence potential 241 9.2.2 Soluble rocks  241 9.2.3 Overconsolidated rocks and rocks susceptible to pore water pressure 242 9.2.4 Tectonics 242 9.2.5 Mass movements  243 9.2.6 Collapses, subsidence and mining subsidence  243 9.2.7 Gas escape  243 9.3 Hydrogeological risks 244 9.3.1 Confined and artesian groundwater  244 9.3.2 Multi-layer groundwater systems 245 9.3.3 Hydrochemical gradients  245 9.3.4 Venting 246 9.3.5 Water quality  246 9.4 Environmental risks  247 9.4.1 Legacy pollution and deposits  247 9.4.2 Mining, mining damage 248 9.5 Risks during BHE installation  248 9.6 Operational risks 249 Literature 253 Glossary 264

About the Author :
The study group Geothermie is a joint study group working since March 2007. Its members are of the section Hydrology of the Deutsche Geologischen Geselschaft - Geologische Vereinigung e.V. (DGGV, formerly DGG) and the section Ingenieurgeologie of the Deutsche Gesellschaft fur Geotechnik e.V. (DGGT) and the DGGV.