Study to Predict In-situ Thermal Properties of Subsurface Soils and Rock

Abstract

In order to further expand the geothermal industry, it is important to evaluate and clarify design and installation methodologies constantly. The soaring prices of oil and electricity have pushed the market to develop more energy efficient systems. For instance, as per Department of Energy Ground Source Heat Pump has ability to reduce the energy consumption from 30% to 60% over its counterparts. In 2017, the geothermal heat pump market was valued at 70.61 billion USD, by the year 2024 it is predicted that the market value will reach 187.72 billion USD. Such rapid growth in the coming years demands more specific data and to move away from current generalized designs. Through the study of published work and virtual sources, it was observed that there was little comprehensive analysis regarding the specific heat of soil and rock. Using prior knowledge of USCS soil classification, our engineers intend to gather distinct specific heat values for identified samples. The collection of thermal properties of individual components such as; soil, grout, HDPE pipe, and distilled water, will aid in developing a theoretical thermal resistance model in accordance to a practical geothermal system underground pipe structure. Tests will be set up to investigate the relationship between soil properties such as moisture and specific heat. Once specific heat values Cp (J/(kg· K)) (BTU/ft· °F) are drawn, conclusions may be developed with regard to critical variables such as thermal conductivity (W /(m· K)/(BTU/(h ·ft·°F)), diffusivity (ft2/s), and specific heat resistivity «K/W)/(h. ft· °F /BTU)); which directly impact the geothermal thermal heat pump design. More accurate data will enhance the coefficient of performance. The research will serve to aid field work as a reliable resource for determination of soil specific heat values, as well as optimize the geothermal system heat exchange behavior as a whole. In short, with increased accuracy of thermal properties, design can then move away from generalized products to more efficient and predictable models. Accurate data will not only optimize geothermal design but reduce test and installation cost, which is helpful to market geothermal for residential and commercial buildings. Ultimately, the increased use of geothermal systems would result in less CO2 emissions and henceforth cleaner air.