太阳能-土壤耦合热泵长年蓄热土壤热平衡分析

以严寒地区季节性蓄热太阳能-土壤耦合热泵系统为研究对象,通过数值模拟的方法,对该系统在长年蓄、取热情况下土壤的热平衡状况进行分析并对系统模型进行实验验证。研究结果表明:系统在相同控制条件下运行,蓄热量大于取热量,土壤温度得到有效提升,但由于连续多年蓄热土壤中出现热堆积现象,蓄热量逐年下降并趋于平稳;土壤温度的逐年升高使热泵COP保持在较高水平,但每年提升的幅度不大,可在土壤平均温度趋于稳定时减少蓄热量,使土壤热量达到平衡。     

跨季节蓄热地源热泵地下蓄热特性的理论研究

研究了跨季节蓄热地源热泵系统(GCHPSS)土壤蓄热体温度场的变化规律,编写VB程序对地下埋管土壤蓄热进行了模拟计算.结果表明:当单U型竖直埋管蓄热时,土壤日蓄热量、热作用半径和平均蓄热率在初始阶段急剧变化,然后缓慢减小并最后趋于稳定,蓄热量也趋于平衡.当管群蓄热时,蓄热系统运行1个循环周期(1a)后,土壤的温度场基本上可以恢复平衡,恢复后较蓄热开始时升高0.5～1.0℃.通过对不同地区3种典型土壤的蓄热进行比较,得出粘土是一种性能良好的长期储能介质.同时,地下埋管土壤蓄热特性的实验研究为GCHPSS系统的推广应用提供设计依据.     

地下水渗流条件下土壤蓄热性能的数值研究

为了研究地下水渗流条件下土壤的蓄热性能及其影响因素,建立了地埋管换热器与土壤的准三维热渗耦合传热模型,通过方程离散和编程求解,研究了地下水渗流条件下渗流速度、U型管管内水流量等因素对土壤蓄热性能的影响规律,对比分析了连续蓄热模式和间歇蓄热模式对土壤蓄热性能的影响,研究结果可为土壤源热泵系统的蓄热运行方式提供参考。     

能源塔—地埋管复合源热泵系统跨季节蓄热实验研究

文章利用能源塔替代太阳能集热系统,在夏季通过地埋管换热器为土壤跨季节蓄热,解决了寒冷地区土壤源热泵冷热负荷不平衡造成的土壤温度过低的问题。分析结果表明,能源塔的蓄热功率会受到土壤温度和环境温度的影响,土壤温度越低,能源塔对土壤的蓄热效果越好,并且能源塔的蓄热功率与环境温度呈正相关。分析结果验证了能源塔—地埋管复合源热泵系统跨季节蓄热在寒冷地区应用具有是可行性。     

严寒地区土壤源热泵地下水平埋管换热性能影响研究

针对严寒地区地源热泵水平埋管换热器的传热规律及其制约因素,建立加土壤保温层水平埋管换热器周围土壤不稳定温度场的物理和数学模型,并对所建立的模型进行模拟计算及实验验证。研究加保温层前后埋管周围土壤的温度变化以及不同运行方式下埋管周围土壤的温度场。结果显示:加土壤保温层后,单埋管换热器周围土壤温度提高1.30℃,双埋管换热器周围土壤温度提高约1.20℃。间歇运行比连续运行更有利于土壤温度的恢复,埋管换热量也得到提高。     

运行模式对土壤源太阳能热泵垂直埋管换热影响的研究

文章设定了土壤源太阳能热泵系统的3种运行模式(连续取热模式、间歇取热模式及间歇取热+蓄热模式),并分别用定热流和等壁温两种方法,对3种运行模式下的垂直U型埋管进行温度场模拟。结果表明:间歇取热+蓄热模式最有利于土壤温度场的恢复,其定热流和等壁温模拟结果一致;等壁温模拟条件下,采用间歇取热+蓄热模式运行24 h后,地埋管取热热流量较间歇取热模式高19.6%,较连续取热模式高36.5%。     

太阳能-土壤源耦合蓄热特性及潜力分析

在分析太阳能与土壤蓄热特点的基础上,提出了利用非采暖季蓄热的节能系统。由于太阳能照射强度具有随季节性变化的特点,非采暖季太阳能辐射强度一般较高,可借助地埋管系统向土壤中蓄热。通过对不同时段太阳辐射强度的监测,在进行数据分析的基础上,建立了太阳集热器数学模型。分析多孔介质蓄热过程的传热传质特性及土壤蓄热特性、非均质性以及地下水径流对热传播半径的影响等特点,提出了在非采暖季进行土壤蓄热的理论和可行性。     

热渗耦合作用下U型埋管换热器的数值模拟

针对土壤耦合热泵地下U型换热埋管,建立了管内流体以及换热器周围土壤热渗耦合物理数学模型。所建模型考虑了U型管的实际形状,土壤考虑为饱和多孔介质,管内湍流流动采用R ea lizab le k-ε模型。采用F luen t软件对模型进行模拟计算,得到了管内流体以及周围土壤温度分布。分析了土壤中水的渗流对传热过程的影响,并对考虑渗流作用时不同土壤物性对单根U型垂直埋管换热器周围土壤温度场进行了模拟计算与分析。     

地下长期蓄热太阳能蔬菜温室

地下长期蓄热太阳能蔬菜温室党建国，凌栋宝０引言土壤中的温度分布是作物生长的环境要素之一。土壤温度可影响根系的生长发育和土壤中微生物的活动。在高寒地区作物越冬，除了要有适宜的空气温度外，还要有适宜的土壤温度。适宜的空气温度可通过构筑温室来实现，而适宜的...     

土壤蓄热与土壤源热泵集成系统的数值模拟

结合土壤源热泵技术推广中存在的问题和地下蓄能技术的优点,提出了土壤蓄热与土壤源热泵集成系统及其地下管群换热器的布置方式。并在能量平衡的基础上建立了地下管群换热器蓄热、释热和停止运行的数学模型。通过数值模拟,分析了埋管间距对蓄热与释热的运行特性的影响。     

蓄热与释热过程中地层温度分布规律的研究

通过对跨季节地源热泵系统的分析,在能量平衡和传热方程的基础上,建立了地层蓄热与释热的非稳态计算模型。分析了地层在蓄热与释热过程中,地下温度场的变化规律;比较了距离埋管不同位置处,沿深度方向的温度分布。研究表明,实际运行中,地层蓄热比地层释热的影响区域大;蓄热时,深部地层的温度低于靠近地表处地层的温度;地层释热时,深部地层的温度高于接近地表处地层的温度。     

Advances in thermal energy storage development at the German Aerospace Center(DLR)

Thermal energy storage(TES)is a key technology for renewable energy utilization and the improvement of the energy efficiency of heat processes.Sectors include industrial process heat and conventional and renewable power generation.TES systems correct the mismatch between supply and demand of thermal energy.In the medium to high temperature range(100~1000℃),only limited storage technology is commercially available and a strong effort is needed to develop a range of storage technologies which are efficient and economical for the very specific requirements of the different application sectors.At the DLR's Institute of Technical Thermodynamics,the complete spectrum of high temperature storage technologies,from various types of sensible over latent heat to thermochemical heat storages are being developed.Different concepts are proposed depending on the heat transfer fluid(synthetic oil,water/steam,molten salt,air)and the required temperature range.The aim is the development of cost effective,efficient and reliable thermal storage systems.Research focuses on characterization of storage materials,enhancement of internal heat transfer,design of innovative storage concepts and modelling of storage components and systems.Demonstration of the storage technology takes place from laboratory scale to field testing(5 kW^1 MW).The paper gives an overview on DLR's current developments.     

岩土含湿特性对传热影响的理论研究

地层储能技术是实现能源可再生和清洁高效利用的有效途径之一,在考虑岩土含湿的基础上,建立了湿岩土体的传热模型,着重分析了在瞬时热源作用下,地下温岩土温度场的演化规律,旨在研究岩土含湿率对其传热特性的影响.分析和计算结果表明,在岩土体临界含湿范围内,岩土含湿率越大,其热传导能力越强,岩土热响应时间越短,越有利于地层中热量的...     

土壤高温储热热湿迁移过程的初步研究

初步建立了土壤高温储热热湿迁移过程的数学模型,并进行了数值求解.结果表明,土壤热湿迁移过程中的湿度场稳定时间明显滞后于温度场,且与土壤类型和水力传导特性等有关.对于水力传导性较差的土壤,在高温储热初期,靠近热源的地方容易产生湿份聚集,使得湿度曲线出现一个短期峰值.与低温储热相比,土壤高温储热时湿度迁移对温度场的影响较大,温度场呈整体降低趋势,降低幅度顺序为:砂土>壤土>粘土.在该文模拟条件下,粘土的热湿迁移过程对于初始湿度的变化不敏感,而砂土的热湿迁移过程则依赖于初始湿度,且影响程度随着初始湿度的增加而增大.     

太阳能跨季节储热供热系统试验分析

介绍了一种太阳能-土壤源热泵联合供热系统,对其运行试验数据进行了分析,并对其运行能效比与两种单独由土壤源热泵供热的模式进行了比较。土壤温度的变化不仅与取热速率有关,还与地温的自动恢复能力相关。该试验建筑所在的土壤条件下地温的恢复能力为30～40MJ/d。采用太阳能-土壤源热泵联合系统能效比最高,土壤源热泵单机组双供系统次之,而土壤源热泵单机组单供系统能效比最低。太阳能跨季节储热及土壤源热泵联合供热系统适用于热负荷远大于冷负荷的建筑。     

Review on solar thermal energy storage technologies and their geometrical configurations

Because of the unstable and intermittent nature of solar energy availability, a thermal energy storage system is required to integrate with the collectors to store thermal energy and retrieve it whenever it is required. Thermal energy storage not only eliminates the discrepancy between energy supply and demand but also increases the performance and reliability of energy systems and plays a crucial role in energy conservation. Under this paper, different thermal energy storage methods, heat transfer enhancement techniques, storage materials, heat transfer fluids, and geometrical configurations are discussed. A comparative assessment of various thermal energy storage methods is also presented. Sensible heat storage involves storing thermal energy within the storage medium by increasing temperature without undergoing any phase transformation, whereas latent heat storage involves storing thermal energy within the material during the transition phase. Combined thermal energy storage is the novel approach to store thermal energy by combining both sensible and latent storage. Based on the literature review, it was found that most of the researchers carried out their work on sensible and latent storage systems with the different storage media and heat transfer fluids. Limited work on a combined sensible-latent heat thermal energy storage system with different storage materials and heat transfer fluids was carried out so far. Further, combined sensible and latent heat storage systems are reported to have a promising approach, as it reduces the cost and increases the energy storage with a stabilized outflow of temperature from the system. The studies discussed and presented in this paper may be helpful to carry out further research in this area.     

Computer analysis,design and simulation of horizontal ground heat exchangers

This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77.     

A new integrated system with cooling storage in soil and ground-coupled heat pump

For the purpose of decreasing the peak electricity, balancing the on and off-peak electric load and utilizing the renewable geothermal energy, a new integrated system with cooling storage in soil and a ground-coupled heat pump is presented. In the integrated system, the moist soil acts as the material for cooling storage, and pipes serve as the cooling storage devices and geothermal heat exchangers simultaneously. In the cooling season, the cooling energy is stored in soil during the off-peak period and is extracted for space cooling during the on-peak period. While in other seasons, the system works as a ground-coupled heat pump for heating or cooling. A mathematical model which describes the charging and discharging processes of the integrated system has been developed and validated, and a computer code has been implemented to simulate the operational performance of cooling charging and discharging in soil. A parametric study indicates that the charging inlet temperature, tube diameter, moisture content of soil and pipe distance are important factors in determining the cyclic performance of the integrated system.