地源热泵岩土热物性测试简介与分析

地源热泵系统作为利用可再生能源的暖通空调技术,具有节能、环保等优点,在世界范围内被广泛使用。土壤作为地源热泵系统的冷热源,对整个系统有着至关重要的影响。不同建筑负荷特性要求系统对土壤的取放热量不同,二者的不平衡会使土壤的温度发生变化,影响整个系统的运行。对特定建筑地源热泵系统土壤的热物性测试是设计地埋管系统的重要依据。本文对热物性测试的理论依据进行了简单介绍,并对具体事例进行了分析计算,得出岩土体的导热系数等具体热物性参数,为地源热泵系统的精确设计提供了依据。     

一种现场测定土壤源热泵岩土热物性的新方法

利用现有土壤源热泵实验台测定了岩土热物性参数,采用传热学反问题的方法对实验数据进行分析。测试过程中从岩土取热,U型地埋管换热器形成一个线热汇,使其在测试过程中与热泵实际运行时的工作状态相接近,测试更准确,节省测量过程的耗电量。以每个采样时刻作为计算节点,取平均值作为计算结果。测定结果显示岩土导热系数为3.2W/(m·K),回填材料导热系数为2.0W/(m·K),岩土热扩散率为0.85×10~(-6)m~2/s。可靠性分析表明:其标准误差分别为0.08W/(m·K),0.04W/(m·K)和0.039×10~(-6) m~2/s。     

不同气候区岩土热物性测试分析

获得准确的岩土热物性是进行地源热泵系统设计的前提,不同的建筑热工气候区岩土热物性不尽相同。依据多年来进行的全国各地区岩土热物性测试,选取严寒地区、寒冷地区、夏热冬冷地区典型城市的测试数据进行对比,阐述测试原理和各地岩土热物性的特点,分析测试结果,得出相关结论,对地源热泵的发展具有一定的指导意义。     

陕西渭南地区岩土热响应测试与分析

地层热物性参数的确定对浅层地热能地源热泵系统的设计至关重要。依托陕西渭南某地源热泵项目,应用恒流法进行了岩土热响应测试,测试共进行了58 h,根据线热源理论对测试数据进行分析计算,求得准确的地层热物性参数,得到工区地层导热系数为2.16 W/(m∙K),比热容为2.39 MJ/(m³∙K),单U地埋管每延米换热量45 W。该研究结果可为项目后期设计与施工提供了相关参考和依据。     

热响应测试在土壤热交换器设计中的应用

分析了土壤热交换器系统的影响因素以及设计与施工中存在的问题,介绍了自主研制的移动式地源热响应测试装置原理与构成。针对天津市某地源热泵项目,阐述了热响应测试的方法与步骤,得到了项目所在地的无干扰地温以及地埋管系统的供回水温度响应曲线。利用线源理论,得到了地埋管换热器钻孔的导热系数及热阻,分析了测试装置与环境的热损失和热增益、测试时间、供电稳定性、无干扰地温、不同深度土壤热导率的变化以及地下水流动对热响应测试造成的影响。测试结论对于指导土壤热交换器设计与施工具有一定的参考价值。     

地源热泵岩土热响应测试方法及数据分析

土壤导热系数的大小直接对土壤源热泵系统中埋地换热器的面积和初投资有显著影响.现场测试法是研究土壤热物性参数最有效的方法之一,结合邢台市沙河收费站地源热泵测试工程实例,介绍了地源热泵热响应测试的测试步骤、测试方法和数据分析.实测结果与传统查手册的结果相比更为准确可靠,为当地地源热泵系统的准确设计提供了依据.     

岩土热响应测试系统的研究与开发

现场热响应测试是实施地源热泵工程的关键环节。本文自主研发了岩土热响应测试系统,既能进行放热试验又能进行吸热试验。用VB语言开发了基于EXCEL的热响应分析软件。该系统及软件在绵阳烟厂得到成功应用,获得了现场土壤原始温度、导热系数以及体积比热、单U管和双u管每延米孔深的吸放热量参考值。测试数据为工程设计提供了依据。     

基于AHP探针法的土壤源热泵现场热响应试验研究

由于探针法和现场热响应试验法为测试岩土热物性参数的常用方法,因此文章基于邢台地区某土壤源热泵工程,将室内探针法和现场热响应试验法确定的热物性参数进行对比分析。首先,根据探针法和现场热响应试验法测试结果的差异,选取地层厚度、含水率、密度及渗透率作为影响土壤样品热物性参数的主要因素,并利用层次分析法来确定各影响因素的权重值;接着,利用各因素的权重值来修正探针法的测试结果;然后,将探针法和现场热响应试验所确定的岩土热物性参数进行比较,得出两个测量结果的相对误差小于10%;最后,对于土壤源热泵项目,文章利用修正后的探针法对现场热响应试验结果进行验证。     

两种深层岩土热物性测试方法的比较

通过对现场热物性测试和现场冷热量测试两种测试方法的对比,说明了各自在深层岩土热物性测试的优缺点。结合实际工程,对两种方法在测试中出现的问题进行分析,指出了现场热物性测试是一种适用范围更广的测试方法。     

基于线热源理论的岩土热响应测试研究现状

地源热泵是可再生能源在建筑物空调中的重要利用形式。岩土热物性是地源热泵地埋管换热器长度设计的主要因素,对于大型埋管系统需要进行热响应测试。回顾了热响应测试的基本原理,介绍了常用的线热源模型及相应的数据处理方法,总结了热响应测试存在的主要问题,并对热响应测试的未来进行了展望。     

基于圆柱热源模型的现场测量地下岩土热物性方法

在埋地换热器圆柱热源模型的基础上采用参数估计法建立了一套可用于现场确定土壤热物性的方法。结合地源热泵系统单井热响应测试实验,计算了地下岩土热物性参数,模拟了管内流体平均温度随时间变化规律,与实验值比较,发现该方法较线热源法更加接近实际。     

Underground energy storage utilizing concrete building foundation: Experimental and numerical approach

Space heating and cooling represent 63% of total building energy demand. In the present study, the concept of concrete foundation piles was used as an underground storage medium. This system requires no additional drilling costs or space, unlike conventional boreholes. A laboratory-scaled experiment facility was designed to experimentally investigate the thermal response of a concrete pile during the charging and discharging processes. The amount of energy stored and released during each process was evaluated. A flow rate parametric study was also conducted to explore the effect of the laminar and turbulent flow behavior. In order to complement the experimental study, an extensive CFD model was developed and compared with the experimental data. There was good agreement between the numerical and experimental results for each process at different flow rates. The results revealed that increasing the flow rate increases not only the heat rejection and extraction but also the storage efficiency.     

Experimental performance of borehole heat exchangers and grouting materials for ground source heat pumps

The system performance of a ground source heat pump (HP) system is determined by the HP characteristics itself and by the thermal interaction between the ground and its borehole heat exchanger (BHE). BHE performance is strongly influenced by the thermal properties of the ground formation, grouting material, and BHE type. Experimental investigations on different BHE types and grouting materials were carried out in Belgium. Its performances were investigated with in situ thermal response tests to determine the thermal conductivity (λ) and borehole resistance (R_b). The line‐source method was used to analyze the results, and the tests showed the viability of the method. The main goal was to determine the thermal borehole resistance of BHEs, including the effect of the grouting material. The ground thermal conductivity was measured as 2.21 W m^?1 K^?1, a high value for the low fraction of water‐saturated sand and the high clay content at the test field. The borehole resistance for a standard coaxial tube with cement–bentonite grouting varied from 0.344 to 0.162 K W^?1 m for the double U‐tube with cement–bentonite mixture (52% reduction). Grouting material based on purely a cement–bentonite mixture results in a high thermal borehole resistance. Addition of sand to the mixture leads to a better performance. The use of thermally enhanced grouts did not improve the performance significantly in comparison with only a low‐cost grouting material as sand. Potential future applications are possible in our country using a mobile testing device, such as characteristics, standardization, quality control, and certification for drilling companies and ground source HP applications, and in situ research for larger systems. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermal resistance and capacity models for borehole heat exchangers

The detailed design and energy analysis of ground source heat pump systems requires the ability to predict the short‐term behavior of borehole heat exchangers (BHE). The application of fully discretized models leads to extensive computation times and a substantial effort in terms of pre‐processing work. On the contrary, analytical models offer simple, parameter input‐based modeling and short computation times, but they usually disregard the transient effects of heat and mass transport in the borehole and hence are not suitable for the prediction of the short‐time behavior. In order to combine the advantages of both types of models, the authors developed two‐dimensional thermal resistance and capacity models for different types of BHE. These models take the capacity of the grouting material with one capacity per tube into account and, therefore, the range of validity is extended to shorter times. The correct consideration of all thermal resistances between the fluid in the pipes, the grout capacities and the borehole wall is important because of the significant influence on the validity of the models. With the developed models, the modeling work and the computation time can be significantly reduced compared with fully discretized computations while precise results are still achieved. The validation of the suggested models against fully discretized FEM models shows a very good agreement. Copyright © 2010 John Wiley & Sons, Ltd.