Effects of multiple ground layers on thermal response test analysis and ground-source heat pump simulation

A modified three-dimensional finite difference model for the borehole ground heat exchangers of a ground-source heat pump (GSHP) system was developed which accounted for multiple ground layers with different thermal properties in the borefield at no groundwater flow. The present model was used to investigate the impact of ignoring ground layers in the thermal response test (TRT) analysis and the subsequent system simulation. It was found that the adoption of an effective ground thermal conductivity and an effective ground volumetric heat capacity for a multi-layer ground determined from a TRT analysis led to very little error in the simulated long term system performance under various ground compositions investigated. The maximum difference occurred for a 3 × 3 borefield in a dual-layer ground which measured 0.5 °C or 3.9% in the rise of the borefield fluid leaving temperature with a cooling-dominated loading profile for 10 years. With the same borefield and ground composition, a dynamic simulation of the complete GSHP system was performed using the TRNSYS simulation software. It was found that the overall system performance based on the present and the old models differed very little. It was concluded that the assumption of a homogeneous ground in a TRT analysis and subsequent system simulation was appropriate and impact of ignoring ground layers was small. A single-ground-layer model, including the analytical models, was sufficient even for a multi-layer ground. This could reduce the computation time significantly, especially when simulating a large borefield.     

Identification of potential areas for biomass production in China: Discussion of a recent approach and future challenges

A standard methodology is needed to recognize potentially suitable areas for sustainable bioenergy crop production. This facilitates better identification of promising crops and cropping systems, logistical and economic studies, and work needed to meet regulatory criteria. A possible approach is built upon three layers of internationally available spatial data: (1) degrading and abandoned areas, (2) potentially suitable land cover classes, (3) exclusion zones such as nature reserves and areas of high biodiversity. For China, areas identified as potentially suitable range from 1.2 to 6.0% of the national territory, depending on different levels of statistical confidence in degrading area status and allowable limits of terrestrial carbon. Verification on the ground showed that about 60% of points tested conformed to the remote suitability assessment in the scenario, which represents the results for the combination of all degrading areas and a terrestrial carbon stock limit of 200 t ha⁻¹. A top-down approach is useful in framing potentially suitable locations, but a complementary bottom-up analysis is still required to ultimately identify areas for sustainable bio-fuel production.     

非均匀环境中的分布目标自适应检测

该文研究了非均匀环境中的分布目标和多点目标的检测。其中,假设辅数据协方差矩阵服从以主数据协方差矩阵为条件的逆Wishart分布,且均值与之成比例。首先给出主数据协方差矩阵、比例因子和目标幅度的最大似然估计(MLE),然后基于贝叶斯理论和广义似然比(GLRT)判决准则提出了一种检测器。当目标只存在单个距离门时,检测器和自适应相干估计器(ACE)一致;当目标跨越多个距离门时,检测器和广义自适应子空间检测器(GASD)一致。但不同在于ACE和GASD都是基于未知的确定干扰协方差矩阵的。另外,该检测器具有恒虚警率(CFAR)特性,并且有很好的检测性能。     

基于贝叶斯理论的一种接力跟踪方法

为了能够利用目标运动信息的先验知识以提高系统的检测和跟踪性能,该文将基于贝叶斯理论的检测跟踪联合处理方法应用于接力跟踪系统中。该方法在贝叶斯理论框架下能够利用系统已经获得的目标运动信息的先验知识,从而提高系统的性能。另外,考虑到计算复杂度,该文给出了一种简化的实现方法多点贝叶斯检测跟踪联合处理方法。该简化方法能够利用基于贝叶斯理论的检测跟踪联合处理方法的优点,同时可以按照系统的计算能力确定并行搜索的点数,以控制系统的计算复杂度。计算机仿真实验表明,在接力跟踪系统中应用基于贝叶斯理论的检测跟踪联合处理方法能够改善系统的检测和跟踪性能。     

非均匀环境中的参量多通道目标检测

该文研究了非均匀环境中的参量多通道目标检测,其中,干扰信号用向量自回归(VAR)模型表示,且模型的空域协方差矩阵服从自由度为,均值为Q的复逆Wishart分布。当Q未知时,文章根据纽曼皮尔逊(NP)准则提出了NP参量自适应匹配滤波器(NP-PAMF),贝叶斯PAMF(B-PAMF)和归一化形式B-NPAMF;当Q已知时,文章根据最大后验概率(MAP)准则提出了MAP-PAMF和归一化形式MAP-NPAMF。结果表明:NP-PAMF和B-PAMF均和有关,当时,B-PAMF趋于经典的PAMF;B-NPAMF与无关,和经典的NPAMF一致。在MAP-PAMF中,空域协方差矩阵的MAP估计由经典估计和先验知识构成,控制后者的权重。最后,文中分析了检测器的复杂度和检测性能。实验表明:贝叶斯的参量检测器具有很好的检测性能,且比归一化检测器的性能优越。     

基于固有模态能量熵的微弱目标检测算法

该文分析了海杂波能量在各固有模态函数(IMF)间的分布特点,研究了目标对海杂波能量在各IMF间分布的影响。研究发现,无目标时,海杂波的能量主要集中于先分解出的3个IMF中,而当目标出现时,海杂波的能量将向后分解出的6个IMF扩散,且固有模态能量熵恰能描述目标出现引起的海杂波能量分布的这种变化,因此该文提出了采用固有模态能量熵检测微弱目标的算法。仿真结果表明,与基于盒维数的微弱目标检测算法、频域CFAR检测方法和多脉冲CA-CFAR(100个脉冲)检测算法相比,该算法的检测性能较好,有效增强了雷达对海杂波中微弱目标的检测能力。     

The use of ground heat storages and evacuated tube solar collectors for meeting the annual heating demand of family-sized houses

The use of storages for sensible heat is limited because parts of the input thermal energy end up as unavoidable heat losses. In order to minimize this loss, it is necessary to keep the surface area to volume ratio (S/V) as low as possible. This occurs when the volume of a body with a certain shape increases. In addition to a large volume it is important to use materials with a high volumetric thermal capacity, as long as sensible heat is being used for storage. This condition is best met by water or a combination of substances with water. In the field of interseasonal storages, for solar heat to cover the heating demands of small residential buildings, the general belief is that the relative small volume needed, results in too much heat loss and therefore individual seasonal storages seem to be of no useful solution.However, the theoretical considerations and simulations in this paper show that this is a prejudice. It is possible to supply a great deal of the thermal energy needed for small residential homes with interseasonal ground storage for solar heat. The loss of heat is acceptable if the storage is designed in the correct way.The ground heat storage should be of cuboidal shape, using the local soil as storage material, if possible. The storage containment must be heat-insulated and damp-proof. The placement of the storage could be within the heated building, adjacent to it or nearby. As such systems may be useful as retrofit for existing houses this study assumes that the storage system has no contact with the heated house. The heat is supplied by evacuated tube solar collectors and their feature to produce effective heat with high temperature (above 100 °C) is used.     

Potential of autonomous ground-coupled heat pump system installations in Greece

The HVAC systems utilizing renewable energy sources are one of the main contributors towards the fossil fuel dependency reduction. Among these, the ground source heat pump systems, especially those based on vertical ground heat exchanger, are very attractive, due to their high efficiency.     

Borehole temperature evolution during thermal response tests

The measurement of temperature inside a borehole at specified depths during a thermal response test, used to infer the subsurface and the borehole thermal properties for the design of a ground-coupled heat pump system, allows the correlation of the subsurface thermal conductivity with stratigraphy. The temperature signal measured in the borehole during heat injection in a ground heat exchanger made with a single U-pipe, however, depends on the location of the temperature sensor in the borehole, which is difficult to determine in practice. Two-dimensional numerical simulations of the borehole temperature evolution during thermal response tests show that the temperature inside the borehole homogenizes rapidly after heat injection is stopped. Monitoring temperature recovery consequently helps to analyze measurements conducted at depth inside the borehole, since recovery measurements are not significantly influenced by the position of the sensor in the borehole. Numerical simulations also indicate that the borehole thermal resistance is best determined using a combination of recovery and heat injection data.     

地基SAR形变监测误差分析与实验

地基SAR(Ground Based Synthetic Aperture Radar,GB-SAR)是进行区域性、全天时、全天候、定点连续形变监测的重要手段。该文对中国科学院电子学研究所研制的地基SAR系统 ASTRO (Advanced Scannable Two-dimensional Rail Observation system)的形变监测性能进行分析,结合ASTRO系统成像几何给出了其形变监测模型和精度分析模型,着重分析了影响形变监测精度的主要误差源。最后以ASTRO系统为实验平台开展了形变监测实验与分析,验证了ASTRO系统用于形变监测的能力。