Heat-Transfer Modeling And Experimental Research On Vertical U-Tube Ground Heat Exchanger Ground-Source Heat Pump In Operation Of The Whole Year

Ground heat exchanger ground-source heat pump (GSHP) system, which has been identified as the most efficient and environment-friendly heating and cooling systems, is one of leading technologies of international HVAC industry. To perfect heat-transfer model for ground heat exchanger is one of key problems about GSHP popularized and applied, so actual thermal behavior of ground heat exchanger can be credibly simulated. This paper summarizes the current research situation of GSHP oversea and home and provides several typical heat-transfer models. This paper presents the all-year experimental results for heating, cooling and renewing soil temperature about a borehole 50 metres in depth installed a single vertical U-tube heat exchanger in Chongqing.This paper introduces the all-year experimental results for GSHP system heating in winter, cooling in summer and renewing soil temperature during the inoperative periods. After a year, soil temperature only increased 0.07 C as compared with initial soil temperature. If only heating in winter, soil temperature decreased 0.96C by contrast with initial soil temperature. It has been proved that the all-year heating and cooling operations are more advantaged than only heating operation in the aspect of renewing soil temperature. During the cooling operation, the impacts of running timescale, different grouts and alternate operation of various boreholes are described. What is more, thermal short-circuit of adjacent legs of a vertical U-tube heat exchanger is researched by experiment. This paper presents that a linear weighted average is used to calculate initial soil temperature. Compared calculated values with experimental results, absolute error is 0.136C, and relative error is 0.69%.For a single borehole, a transient one-dimensional line-source model outside borehole and a steady-state model inside borehole are presented. These models consider the time-varying loads used superposition solution by heat pulse analysis and also consider intermittent operations of heat pump. Based on a single borehole, multiple boreholes heat-transfer model is achieved by a superposition technique. Compared calculated values used these models with experimental results, average error is 2.48%, and maximum error is 7.87%.This paper analyzes various factors inducing variation of temperature at the borehole wall and describes development trend of time-varying temperature at theborehole wall. In the borehole thermal resistance, the effects of grout thermal resistance, pipe thermal resistance and convection thermal resistance on heat rate are analyzed. This paper presents the impact of configurations of a single U-tube in the borehole and of laminar and turbulent flow on heat rate. This paper introduces an experimental technique to validate the borehole thermal resistance. Furthermore, the effects of the borehole thermal resistance and ground thermal resistance on temperature of heat carrier fluid are presented.