Experimental Study On Heat Transfer Characteristics Of Wet Soil Based On Ground Source Heat Pump System

Geothermal energy is a renewable energy.The earth's geothermal energyresources are huge,much more than the fossil energy reserves.Ground source heat pump(GSHP)system is an effective way to utilize geothermal energy,it is a heat pump system with soil as heat source or cold source.In the practical application of the ground source heat pump system,the buried pipe is in the form of a well group.In the actual geological conditions,unsaturated soil exists widely.In this paper,the heat transfer characteristics and influencing factors of a simple well group system composed of double buried pipe system in dry soil,saturated soil and unsaturated soil are studied.Thus,it can provide theoretical basis for the design and optimization of the ground source heat pump system.In this paper,based on the experimental platform of soil source heat pump system,the underground heat transfer characteristics,influencing factors and Energy efficiency characteristics of 3 kinds of soil(dry soil,saturated soil,unsaturated soil)under different operating modes(Continuous operation of single buried pipe,continuous operation of double buried pipes and intermittent operation of double underground pipes)were studied.The results obtained are as follows.(1)Comparison of soil temperature field between single buried pipe and double buried pipe in ground source heat pump system in 3 kinds of soil.The heat extraction radius of U type buried pipe and distribution characteristics of soil temperature field is obtained.(2)Intermittent operation of ground source heat pump system in 3 kinds of soil.The change of soil temperature with time and optimal batch mode was obtained.(3)In this paper,the soil water heat transfer between the double U type buried pipes is analyzed under the condition of seepage flow in saturated soil.The effects of intermittent operation of the system under different flow rates,the intermittent operation of the system with different seepage velocity and the different intermittent operation of the same seepage velocity on the heat transfer between the two buried pipes are obtained.(4)The soil temperature field and energy efficiency of different operation modes in 3 kinds of soil environments were compared.The effects of 3 kinds of soil environments on the heat transfer and energy efficiency were obtained.It is concluded that unsaturated soil is the most suitable soil environment for ground source heat pump.