In-situ Thermal Response Test And Simulation For Ground Source Heat Pump Systemperformance

Thermal response test is the basis for the design of ground source heat pump(GSHP).The traditional thermal response test needs stable power inputs whose tiny fluctuations will result in larger testerror.In addition,the soilthermal conductivity will be obtainedbutthe total thermal resistance of the boreholeand soil heat capacitycannot be directly drawn from the traditional thermal response test.This studyproposed a heat transfer model,and validates this model by the field test data.In the process of thermal response test,the heating power can be any change,and even the power outage also does not affect the test results.Not only the accurate of the soil thermal conductivityobtained by the numerical calculation is improved,but also the thermal resistance of the boreholeand the heat capacity of soil can be calculatedby the thermal response test.For GSHP systems with multiple boreholes,the calculation results from single boreholemodel seldom matchthe real values.To establish a three-dimensional boreholegroup of calculation modelsis quit hugein practicalprojects,the boundary conditions need to be re-established when the boreholes' layout,spacing or numbers adjusted.This paperassumed that each boreholeis in the center,which simplifies the boundary conditions of the borehole group.Ifthe design is changed,only the parameters such as boreholespacing,boreholenumber are changed to conduct the simulation of new GSHP system.As the model is reasonable only on the condition of infinite number of boreholes,the boreholegroup coefficient is introduced to reduce the error of the hypothesis.Ifthere is only one borehole,the boreholegroupcoefficientis 0;and if the boreholenumber is infinite,the borehole groupcoefficient is 1.If the boreholenumber is a specific value,the coefficient is calculated by a model.Tested on a real project,the simulated results exhibit high accordance with the measured.Inmost regions,theheat rejection in summer and extraction in winterare always imbalancein GSHP systems.In the Yangtze River valley in China,the heat rejectedto underground in summer is 3 timesthan the heat extractionin winter.The underground heat exchanger in GSHP system cannot running sustainable.This paper employs the GSHP combined with ice storage systemwhosecondensing heatdischarges through the cooling tower.The coordination operation of two systems can solve the problem of underground balance of winter and summer,and can save the operating costs of air conditioning systems by shiftthe peakelectricity consumption from on-peak hours to the off-peak hours.As an unsteady process,the ice making process is divided into three stages: water cooling,super-cooled water eliminating,and iceforming.Each stage in the corresponding heat transfer model is established.In a real ice storage system,the field test is conduct to verify the validity and reliabilityof the ice building model calculation results.Asimulation model ofGSHP combined with ice storage system is developed.In summer,GSHP,chiller and the ice storage device can workeither independently or cooperatively.In order to meet the requirement of air conditioning load as well asto keep underground heat balance of heat extraction in winter and heat rejection in summer and to save operating costs,a model is developed to forecast load and to optimize the running mode.In terms of load forecasting,fuzzy recognition model is established,and makes the forecast more accurate and stable.The optimal control model adopts the methodof trial step by step.The software is applied and validated in a practical project.In the end,a simulation software is developed by integratethe thermal response test model,the boreholegroup model of GSHP,the ice storage model,the model of load forecastingand optimization control.Input the annual dynamic load,the software can realize the equipment selection and the operatingsimulation of the GSHP combined with ice storage system.