Fluid Mechanics of geothermal heat pumps
|In this thesis we have examined the application of fluid mechanics and heat transfer principles in GSHP systems for operation in cold climatic conditions.
First, we developed analytical models that describe the 1-D and 2-D flow and heat flux regimes in order to provide a mathematical understanding of the phenomena that take place in the ground and of how they may affect the Ground Source Heat pump operation. This analytical modelling was based on fluid mechanics and heat transfer principles.
Second, we developed a numerical model so that we could provide a useful and flexible tool in the process of understanding more specific and sophisticated cases that could not be solved analytically. The numerical scheme proved to be in agreement with the analytical solution. We have the confidence that the numerical model works and that it can be used to explore more difficult modes of operation.
Third, we performed a series of experiments to model the physical phenomena involved in the heat transfer and fluid flow for the 1-D case of the problem. Taking into consideration that some of the model conditions, such as perfect thermal insulation from the environment, could not be achieved, the experiments confirmed the analytical and numerical models.
Finally, concerning the implementation of GSHPs, we have suggested possible improvements for the design and the operation of these systems. The understanding of their operational features and the interaction of the Heat Pump with the ground thermal source or sink, as well as the reaction of the soil led us draw some useful conclusions. One of the most important is that according to our findings a lower number of well bores can be used for the same amount of energy production if the ground temperature drops below 0oC. The installation of fewer well bores implies lower capital cost. This can render Ground Source Heat Pumps more attractive economically and shall help increase the rate of installation of these low energy systems.