| Ground source heat pump (GSHP) air conditioning systems utilize ground soil as a heat source/sink, achieve heat transfer between the ground soil and a working fluid (water or antifreeze solution) circulating in a closed loop buried in the ground. Compared to other conventional alternatives, the ground source heat pump system makes full use of renewable energy, and boasts the features of protecting the environment and reducing electric power consumption. It has been applied in Europe and American for a few decades. In recent years the technology has been paid attention to also in China, and a few GSHP pilot projects have been completed here. However, researches on design of the geothermal heat exchanger (GHE), performance predictions of the GSHP systems and system optimization are far from adequate. Besides, no national standards and criteria are promulgated for the GSHP systems. This situation impedes its application.Acknowledging the support from the key research project of The Science and Technology Bureau of Shandong Province, the thesis has accomplished studies on respective components of the GSHP air-conditioning systems, and set up analytical models of the entire system on the principles of mass and energy conservation. Main contents and results of the thesis are as follows.(1) Modeling of the vertical GHEs. Heat transfer in a single borehole of the GHE is analyzed in two separate regions, i.e. the inner region within the borehole wall and the external region beyond this boundary. In the external region, heat transfer between the U-tube borehole and the ground is considered with a model of a finite line-source in a semi-infinite medium, and it is the first time to achieve an analytical solution of the temperature distribution for a such a transient two-dimensional conduction problem by means of the Green-function method. According to this solution, the representative temperature response in a borehole wall can be determined, which varies with time under the condition of constant heat flux.Compared to heat transfer in the external region of borehole, mass and heat capacity of materials inside the borehole are insignificant and negligible. Thus, heat transfer inside the borehole is approximated as steady-state heat transfer except for analyses of short times (a fewhours). With the convective heat transfer of the fluid in U-tube pipes along the borehole depth considered, a quasi-three-dimensional model is built. By the theoretical analysis, the temperature profile of the fluid along the borehole axis, and then, the fluid inlet and outlet temperatures can be obtained. The concept of GHE efficiency is also introduced to discuss the effect of GHE construction parameters on its performance, especially that of thermal short-circuiting in the two branches of the U-tube.The geothermal heat exchangers often consist of a number of boreholes. Besides, practical load of the GHEs varies with time. The variable load of GHEs is decomposed as a series of pulse load, and the superimposition principle is employed to obtain the real temperature response of the GHEs on basis of the theoretical solutions of a single borehole experiencing a constant heat flux.According to above model a GHE design procedure is presented, in which the temperature of circulating fluid is kept within desired limits in its entire life cycle. By inputting the monthly load of the air-conditioning system, design and simulation software of GHEs is developed.(2) A steady-state model for a water-to-water heat pump. By means of lumped parameter method a reciprocating compressor model and a thermostatic expansion valve model are set up. Meanwhile, in a distributed parameter approach a steady-state model of condenser and evaporator has also been established in the form of concentric counter-flow heat exchangers. In this study the revised Xtt formula are used to calculate void fraction correlation in the two-phase region of condenser and evaporator. A refrigerant charge model is established to predict the effect of refrigerant charge inven...
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