Improvements of U-pipe Borehole Heat Exchangers

3 PREFACE 4 ACKNOWLEDGEMENTS 5 PUBLICATIONS 6 ABBREVIATIONS AND NOMENCLATURE 7 TABLE OF CONTENTS 10 INDEX OF FIGURES 11 INDEX OF TABLES 14 1 INTRODUCTION – BASIC CONCEPTS 15 1.1 GROUND SOURCE HEAT PUMPS 15 1.2 THERMAL PROCESSES IN THE GROUND 18 1.3 SECONDARY WORKING FLUID FLOW 20 1.3.1 Hydrodynamic considerations 21 1.3.2 Thermal considerations 21 1.4 THERMAL RESISTANCES IN BHES 23 1.5 THERMAL RESPONSE TEST 26 1.6 BOREHOLE HEAT EXCHANGERS-STATE OF THE ART 29 1.6.1 U-pipe BHEs 30 1.6.2 Coaxial BHEs 32 1.7 DISTRIBUTED TEMPERATURE MEASUREMENTS 33 2 EXPERIENCES WITH U-PIPE BHES 39 2.1 DESCRIPTION OF THE INSTALLATION 39 2.2 TEMPERATURES DURING HEAT PUMP OPERATION 43 2.3 DISTRIBUTED THERMAL RESPONSE TEST 50 2.4 DISTRIBUTED PRESSURE MEASUREMENTS 57 3 EXPERIENCES WITH ALTERNATIVE U-PIPE BHES 61 3.1 THEORETICAL EVALUATION 62 3.2 EXPERIMENTAL EVALUATION 67 4 EXPERIENCES WITH COAXIAL BHES 76 4.1 AN ANNULAR COAXIAL BHE FIRST PROTOTYPE 76 4.2 COAXIAL PROTOTYPE WITH FIVE EXTERNAL FLOW CHANNELS 80 5 CONCLUSIONS 90 6 REFERENCES 95