A Simulation Tool For Ground Loop Heat Exchangers In Ground Source Heat Pump System

Ground source heat pump(GSHP) is a device where heat exchange is completedbetween the heat exchanger systems buried around the building and inside of thebuilding using relatively stable characteristics of underground soil temperature, whichis important technological means for building energy saving and environmentalprotection. Ground heat exchanger (GHX) is an important part of the ground sourceheat pump system. The heat transfer between GHX and the surrounding soil is acomplex, non-steady-state process and the key to the ground source heat pumptechnology which decides the success of the entire system. In this paper, the verticalGHX is the main object of study and the heat transfer inside and outside the boreholeare studied respectively. The three-dimensional non-steady-state heat transfer model issimulated to analyze the impacts of borehole parameters and fluid flow rate etc. on theheat transfer process. For the optimization of GHX design, uncertainty factors aboutthe pipe length calculation are researched. The load algorithms are improved toincrease the speed of simulation and simulation tool is designed to calculate therequired pipe length and the entering temperature of the circulating fluid, making auseful exploration of reducing the initial investment of the project. The researchworks include:1. At the boundary of the borehole wall, heat transfer area is divided into twoparts in the borehole and outside the borehole. The heat transfer model outside theborehole is established by the limited long-term heat source method and the averagetemperature of the borehole wall can be got by superimposition of G-function. Theheat transfer model in the borehole and heat pump model are established to calculatethe relationship between the load of the heat pump and the entering fluid temperatureto the heat pump.2. A three-dimensional non-steady-state heat transfer model is established andthe numerical simulation is used to analyze the impacts of the circulating fluid flowrate, grout thermal properties, U-tube shank spacing and borehole depth on the heattransfer of ground heat exchanger in ground source heat pump system.3. The formula of ground heat pipe length is introduced and a computing methodis put forward to analyze the uncertainty factor in the calculation of the ground heatexchanger length. An instance is shown to analyze the impacts of the uncertainparameters on the length calculation of the ground heat exchanger. 4. The design methodology is introduced in the ground loop heat exchangerdesign tool. The design methodology is based partly on the G-function developed byEskilson, partly on a simple heat pump model that represents the ratios of the heatrejected to the ground to cooling provided and heat extracted from the ground toheating provided, and partly on a simple analytical approximation for the response ofthe ground loop heat exchanger to a single peak heat extraction or rejection pulse. Thesimulation process of design tool is shown by a project instance and the simulationresults are analyzed. At last engineering data are collected to verify the reliability ofthe simulation tool.