Theoretical and experimental study of geothermal spiral heat exchangers: Heating and cooling with heat pumps, and dimensioning systems

This thesis consists in a study of geothermal helical heat exchangers buried in the close underground. These objects belong to the compact exchangers kind and may be used instead of borehole heat exchanger or geothermal horizontal exchangers to cope with the needs in heating and cooling buildings with a heat pump. A theoretical and experimental study of these exchangers leads to numerical and analytical models which can be used to estimate the temperatures in the underground and in the exchanger over years. Results of simulations including a building are given, and softwares were developed to help with the sizing of installations. Moreover, a specific 'thermal response test' for helical heat exchangers was developed, in order to estimate the mean thermal properties of the underground and the thermal resistance between the heat transfer fluid and the underground. At least, practical advices are given, which goal is to get more valuable temperatures at the heat pump and as a consequence better coefficients of performance of the geothermal system. (author)