Rapid Method Of Calculation For Vertical Heat Exchangers And Software Development

Ground source heat pump(GSHP) is a kind of energy-saving and environmentalprotection air-condition system, which are able to transform the shallow geothermalenergy to a higher level, then provide heating and cooling for the building. As atechnology utilizing renewable energy, GSHP has been widely used in a variety ofresidential and commercial buildings. The study of geothermal heat exchangers is thecore of research into the GSHP. This paper focuses on the analysis and comparison ofheat transfer model of drilling outer, detailedly analyzed and compared variousmethods of calculated time. Fast calculated software for heat transfer analysis ofunderground pipe was developed to analyze heat transfer efficiency in different pipeform.Firstly,For the study of heat transfer model outside the borehole wall ofunderground pipe, based on the finite line source model, the author uses fast Fouriertransform to deal with the form of convolution processing in analytical solution. Byimproving it from the old g-function to the new one, the computing speed is greatlyaccelerated. Through series of comparisons of the calculation time of several analyticsolutions with g-function or δ-function, we found that the calculation time of averagetemperature of underground pipe is longer than the midpoint temperature.Besides theimprovement of the calculation speed is not obvious for the previous δ-function afterthe using of fast Fourier transform, nevertheless, the calculation speed of newδ-function increases greatly, which made it more easily to be applied to engineeringpractice.Secondly, optimize the ground heat transfer analysis software mentioned in theliterature[37]continuously. By adding the possible forms of buried pipe in actualprojects, the forms of tube group layout are expanded from one to six in the software.Heat transfer model and calculation method of each module is detailed along with thepossible problems and ways to deal with them.Thirdly, through a specific experimental setup of GSHP, the heat transferanalysis software was validated, and the error of their produce was detailed analyzed.The error mainly comes from the simplified analytic solution model and dramaticchange of the heat flow of the fluid within the pipe. It was revealed that the COP ofGSHP can be improved in the case of intermittent operation and regular switch of hot and cold mode. Based on the correctness of heat transfer analysis software forunderground pipe, heat transfer efficiency of different types of buried pipes areanalyzed and a higher heat transfer efficiency form was obtained by comparing of thefluid temperature through the tube.These studies of research make the use of ground heat transfer analysis softwarepossible in practical engineering applications, which provides a powerful andconvenient tool for fast computation and analysis of the heat transfer performance forreal a project in the future.