A Study on the Calculation Model of Rock Soil Thermal Conductivity in the Design of the Ground Source Heat Pump System

The rock soil thermal conductivity is the most important design parameter for the ground source heat pump system. Based on the equation applied for the heat transfer between the geothermal heat exchanger and its surrounding rock soil, a quasi-three dimensional heat conduction model showing the heat transfer inside the borehole of the U-tube was established to determine the thermal conductivity of the deep-layer rock soil. The results obtained show that the average thermal conductivity got through calculation and actual determination in a tube-embedding region of the ground source heat pump engineering were 1.895 and 1.955W/(m center dot degrees C), respectively. The soil layer, which has a great thermal conductivity and a strong integrated heat transfer capability, is suitable for the use of the ground source heat pump system with the tubes embedded underground. The soil layer, with a body temperature of 19 C and a higher initial temperature, is suitable for the heat extraction from underground in winter. The deviation between the calculation and the determination of the average thermal conductivity in the abovementioned region was 0.06, which could meet the required precision, indicating that the results from the calculation could be used for design. Along with the economic development, the problem of energy crisis has become increasingly prominent ([1]). The statistics show that the energy consumption of buildings accounts approximately for one third of the commercial energy consumption of the whole society; however, the energy consumption of Heating, Ventilation and Air Conditioning (HVAC) system accounts for about 60% of that of buildings and is one of the fields most potential in energy conservation ([2]). The Ground Source Heat Pump (GSHP) is a new type of energy utilization technology, in which the shadow geothermal energy is used for the heat supply and refrigeration and this technology can be applied to alleviate the energy pressure ([3,4]) of our country to a certain extent due to the reasons as follows: the heat pump is merely used for the heat transfer, not for its generation and over 70% of the required heat is from underground; the electricity required for transferring the heat from buildings to underground is very little. The thermal conductivity of rock soil is the most important design parameter of the GSHP engineering. Pursuant to the practices carried out in engineering, the author will conduct a systematic study on modeling and determination methods of thermal conductivity of rock soil and offer a scientific basis for GSHP engineering in this paper.