Heat Transfer And Thermal Performance Of The Vertical Downhole Heat Exchanger For Ground Source Heat Pumps

Supported by the National Natural Science Foundation of China(Study on Heat Transfer Characteristics of Downhole Coaxial Heat Exchanger in Convection Geothermal Reservoir )and Tianjin Development and Plan Program of Science and technology(Study of Ecologic Architectural Energy System), the thermal performance exploiting earth energy for heating and cooling is studied in this paper,and its main purpose is to offer reference for increasing the percent of renewable energy in Ecologic Architectural Energy. As a renewable energy, underground thermal energy is presented in this paper. Research method used by this paper is simulating experimentally indoor or outdoor firstly, and afterwards, a new approach is presented in order to emphasis the theoretical study, which according to water-enriched and water-lacked, the heat transfer performance of soils and rocks is separately studied theoretically,and Critical Water Content is submitted specifically as a reference to divide them. For a soil of water-enriched, a steady theoretical model is developed for Downhole Heat Exchanger (DHE) embedded in a saturated porous medium, based on combined with theory study and indoor imitation experimental equipment, and dimensionless heat transfer regularity of saturated porous medium is summarized. A lot of results are made from calculating of case for Geothermal Reservoir property of earth energy within 200～2000 (m.℃), it is helpful to analysis influence of permeability coefficient , kinematic viscosity and thermal diffusion coefficient of soils and rocks on heat transfer performance. For a soil or rock of water-lacked, a heat transfer theoretical model is developed, which is a steady or unsteady, the results show that Reservoir temperature, thermal diffusion coefficient, inlet temperature, flow rate of and run time of ground source heat pumps have an effect directly on heat transfer process of DHE.It can deduce that intermit running is favorable for this type of soils and rocks.In this paper, some principles are submitted to analysis performance of energy saving. It is further pointed out the key and direction for enabling large-scale of underground thermal energy, by means of discussion of evaluation index, and economy performance.