【作者】 贾捷；

【导师】 张欢；

【作者基本信息】 天津大学 ， 供热、供燃气、通风及空调工程， 2012， 硕士

【摘要】 地源热泵系统是一种利用地下岩土作为热源和热汇的空调系统,由于其具有低碳、节能的优势,已经在我国得到了广泛的应用。在实际应用中,地源热泵系统的性能及经济性很大程度上取决于当地土壤的导热系数。《地源热泵系统工程技术规范》(GB50366-2005)推荐采用现场热响应试验的方法来确定这一热物性参数,其原理是通过传热介质在地埋管换热器中循环,在给定的放热量或取热量下,连续记录流体的进出口温度,并根据温度随时间变化的规律推知土壤导热系数。传热流体在地埋管换热器中流动的平均温度是计算土壤导热系数的基础数据,一般认为流体平均温度等于地埋管进出口流体的算术平均温度,这一方法虽简单但缺少理论依据,本文利用CFD软件FLUENT模拟了典型热响应试验中流体的三维非稳态温度场,发现算术平均温度与流体的积分平均温度相差并不大,在工程实际中完全可以用来代表流体的平均温度。传统的热响应试验仪只能测量土壤热响应,而忽略了土壤的冷响应。针对这一局限性,本文构造了一种新型土壤热响应试验仪,与传统试验仪相比,本试验仪可以同时测量土壤的热响应和冷响应,且具有运行稳定、测试结果精确、所需测试时间较短的特点。本文还提出了一种基于二维有限长线热源模型的测试数据处理方法。运用新型热响应试验仪在天津某地进行了热响应试验,并用上述数据处理方法得到了当地的土壤导热系数,通过对比不同工况下所得的土壤导热系数发现该方法比传统方法更为可靠,所得结果可以反映地埋管换热器的全年运行条件。最后,为了便于工程应用,本文还利用MATLAB编制了对应于该测试数据处理方法的计算界面,用户可在此界面中输入相应数据,并得到设计中所需的土壤导热系数。此外,由于基于二维有限长线热源模型的测试数据处理方法有其自身的局限性,本文还提出了一种基于数值模型的参数估计法用来在热响应试验中计算土壤及回填材料的导热系数,将此方法用于前述热响应试验,并对比了分别运用二维有限长线热源模型和数值方法所得的土壤导热系数,发现两种方法所得土壤导热系数之间有一定偏差,最后分析了产生这一偏差的原因。更多还原

【Abstract】 Utilizing the ground as heat source and sink, ground source heat pump (GSHP) system has the advantage of lower carbon dioxide emissions and higher energy efficiency compared with conventional system. As a result, it is widely used at present in China.In practice, the thermal performance and economical efficiency of GSHP system is largely dependent on the local ground thermal conductivity.“Technical Code for Ground Source Heat Pump System”(GB50366-2005) recommends using the in-situ thermal response test (TRT) to determine this thermal property which is based on injecting or extracting a constant heating power to or from the ground and measuring the inlet and outlet fluid temperatures continuously during the test, and then the ground thermal conductivity can be calcalated from the measured temperature history.The average temperature of circulating fluid in BHE is the basic test data for computing the ground thermal conductivity. Conventionally, the arithmetic mean value of inlet and outlet temperatures is taken as the average fluid temperature, this method is simple but lack of theoretical foundation. This paper used the CFD software FLUENT to simulate the three-dimensional transient temperature field of circulating fluid in a typical TRT and found that the arithmetic mean temperature has little difference with the volume integration temperature. So, in practice, it can be used to represent the average temperature of circulating fluid.Conventional test equipment can only conduct the heat injection test. Focus on the situation, this paper constructed a new kind of test equipment for TRT. Compared with the conventional test equipments, this test equipment can conduct the heat injection and extraction tests simultaneously, in addition, it is more stable while running and requires much less test duration.Moreover, this paper proposed a new data analysis method based on the two-dimensional finite line source model. With the new test equipment a TRT was conducted in Tianjin, and the ground thermal conductivity was determined by the data analysis method. By comparison, it was found that this method is more accurate than conventional methods, and the resulting ground thermal conductivity can reflect the annual operation condition for BHE. Besides, for the convenience of engineering application, the paper developed a computing interface corresponding to the data analysis method based on MATLAB. The users can input relative information and get the ground thermal conductivity in this interface.Finally, it should be noted that the data analysis method based on the two-dimensional finite line model has some limitations, so this paper also proposed a parameter estimated method based on the one-dimensional numerical model to evaluate the thermal conductivity of ground and grout. Applying this method to the TRT mentioned above, the resulting ground thermal conductivity was compared with that resulted from the analytical method, and it was found that there was a bit difference between the results. The reasons for this difference were also analyzed.更多还原