地下水源热泵采能区水热耦合模型研究

为合理安排地下水源热泵系统的抽灌井布局,利用地下水数值模拟方法,通过Visual MODFLOW软件中的SEAWATV4热运移模块,概化地下水温度场运移过程,建立了符合研究区域水文地质特征的水热耦合数值模型,采用不同的变量对合理井距离进行模拟研究,模拟得出在水温变幅不超过2 ℃的前提下,抽灌量300、800、1 500、2 500 m3/d的合理井距分别为26.5、53.0、80.0、106.0 m,可知温度场的变化范围受井距和抽灌量影响明显并呈一定规律性,应根据水源热泵系统不同的抽灌量要求确定合理的抽灌井距离。     

地下水源热泵不同布井模式下地下温度场变化模拟分析

针对地下水源热泵抽水井与回灌井布局模式对地下温度场的影响,通过建立地下水流与温度的耦合模型,从抽灌井布置间距及抽灌井数量角度模拟分析了不同布井模式下地下水温度的变化趋势和热贯通发生的基本特性。结果表明,同类井间距对热贯通影响不显著,抽灌井间距对抽水温度及热贯通时间影响较大;从热贯通发生时间来看,抽灌井数量越多热贯通发生的时间越延迟,但从温度偏离度角度分析,系统长期运行后抽灌井数量对抽水温度偏离度影响不显著。     

冷热负荷失衡条件下采能区地温场的模拟研究

以北京某地下水源热泵空调系统为例,利用地下水、热耦合数值模型技术,对冷、热负荷严重不平衡条件下地下水抽灌场地温度场的年内和年际变化进行了定量模拟预测研究,并对系统长期运行的可行性进行了论证.研究结果表明:抽水井和回灌井之间的距离相对较大,抽灌井之间的"热突破"程度较低;由于空凋系统的供暖负荷显著大于制冷负荷,抽灌区温度场将呈逐年下降趋势;抽灌场地是一个开放的系统,不断与外界发生能量交换.随着热泵空调系统的长期运行,抽灌区的温度下降速率越来越小,地温场渐趋稳定;由于热泵系统的年内冷、热负荷存在严重失衡,进而对热泵系统的运行效率将产生一定影响.     

热渗耦合的地下水源热泵抽灌井传热数值模拟

基于达西定律,分析了饱和区土壤中地下水源热泵抽灌井传热机制,构建了热渗耦合共同作用下的数学模型,研究了有无地下水渗流及渗流速度对抽灌井周围温度场变化的影响,使用COMSOL Multiphysics软件对建立的模型进行了分析模拟.实例结果表明,该模型具有较好的适用性,为系统的优化设计与参数合理匹配提供了理论支持.     

地下承压含水层水-热运移特性的模拟研究

依据地下水文地质的相关概念和渗流力学的理论基础,建立了地下含水层热量运移的数学模型.以微山地区一工程为背景,对1抽2灌井群的热量分布规律进行了求解,得出了井群的水流速度场、水头压力场以及温度场分布.经计算分析得出:①在抽灌状态下,水压的变化较温度场快,影响范围也较大.相对应的温度影响半径相对较小,变化速度较慢且不明显;②温度场的影响半径主要集中在井周围约30m范围内,其温度的变化梯度为0.17℃/m.而超出此范围的区域,影响的相应时间较长,幅度不大;③夏季抽灌温差采用:10℃大温差运行,有利于避免或减小热贯通现象,且可减少抽灌水量.     

地下水源热泵运行期间水热变化模拟分析

为探究地下水源热泵运行期间水热变化特征,以三门峡市地下水源热泵工程为例,通过HST3D软件中的FlowHeat模块,采用现场验证的概念模型与数学模型模拟了抽灌井制冷期(92d)运行工况。结果表明,在目前工况条件下,地下水水热变化对水源热泵利用工程影响不明显,发生热贯通可能性较小。     

常温注水井对含水层热贯通的影响机理分析

为探究常温注水井对水源热泵热贯通现象的影响,利用FlowHeat1.0软件模拟了3组情景下含水层渗流场、温度场时空分布特征,并分析了常温注水井对含水层热贯通的影响机理和抽水井水温变化规律。结果表明,常温注水井通过减小回灌井、常温注水井之间的水力坡度和延长地下水渗透途径的方式达到缓解热贯通的效果;回灌井、常温注水井流量比相同时,常温注水井在抽灌井连线的位置对含水层热贯通的影响小;抽灌量不变时,常温注水井与回灌井的流量比越大,常温注水井缓解热贯通的效果越明显;在有利地下水回灌的水源热泵系统中,布设常温注水井能有效地降低含水层热贯通程度。     

热泵耦合含水层储能技术研究

结合实际工程项目,对对井抽灌热泵耦合地下含水层储能效果进行了研究与评价.结果表明热泵耦合含水层储能系统能够充分利用浅层地能资源,实现冬灌夏用和夏灌冬用的储能作用,节能效果显著.但是,在冷热负荷不平衡的情况下,若系统长期运行会造成采井或灌井周围温度的降低或升高.因此,为了保护地下生态平衡,系统应尽量在冷热负荷均衡的工况下运行.     

水源热泵系统应用研究——以礼士宾馆水源热泵系统为例

礼士宾馆于2002年进行锅炉改造，采用水源热泵系统代替燃煤锅炉进行冬季供暖，同时夏季进行制冷。水源热泵系统的设计和安装工作是由专业队伍承担的，通过详细的水文地质调查，在宾馆四周布置了4眼抽灌井，施工过程中严把质量关，使各井满足了供水和回灌要求。2003年底，系统开始运行，采用一抽两灌方式，目前已经正常运行3个供暖季和2个制冷季，通过对该系统进行的长期动态监测，获得了大量真实可靠的数据，为研究水源热泵的应用条件提供了依据。     

井对间距与含水层采能区温度场的演化关系

抽、灌井对之间的距离是地下水源热泵采能工程设计中的重要参数之一。该文应用数值模拟的方法对不同井对间距条件下地下含水层采能区温度场的演化进行了定量模拟,并对地温场的演化规律与井对距离之间的关系进行了理论分析。研究结果表明,抽、灌井对距离越大,抽水井温度变化速度越迟缓,且温度变幅越小。其原因是:井对距离越大,渗流区水动力影响范围越大,抽、灌区等效渗流速度越小,回灌水向抽水井运动过程中散热(吸热)越充分。     

Open-loop groundwater heat pumps development for large buildings: A case study

A study of the feasibility of providing the heating and cooling needs of the new, large commercial building near Turin, Italy, by means of an open-loop indirect groundwater heat pump (GWHP) system is described. A finite element subsurface flow and transport simulator (FEFLOW) was used to investigate possible configurations of extraction and injection wells for five different scenarios. Modelling results confirmed the hydrogeological capacity of the site to provide the necessary amount of groundwater and associated energy with limited environmental impact. Injection of warmer (or cooler) water in the aquifer creates a thermal plume whose dimensions and geometry depend on the properties of the subsurface formations, particularly their thermal dispersivity values. The study suggests that there are several possible well configurations that could support the GWHP system without adversely affecting the aquifer.     

Optimization model analysis of centralized groundwater source heat pump system in heating season

The ground-water heat-pump system (GWHP) provides a high efficient way for heating and cooling while consuming a little electrical energy. Due to the lack of scientific guidance for operating control strategy, the coefficient of performance (COP) of the system and units are still very low. In this paper, the running strategy of GWHP was studied. First, the groundwater thermal transfer calculation under slow heat transfixion and transient heat transfixion was established by calculating the heat transfer simulation software Flow Heat and using correction factor. Next, heating parameters were calculated based on the building heat load and the terminal equipment characteristic equation. Then, the energy consumption calculation model for units and pumps were established, based on which the optimization method and constraints were established. Finally, a field test on a GWHP system in Beijing was conducted and the model was applied. The new system operation optimization idea for taking every part of the GWHP into account that put forward in this paper has an important guiding significance to the actual operation of underground water source heat pump.     

International legal status of the use of shallow geothermal energy

Shallow geothermal energy (<400 m depth) is used in many countries worldwide, with a rising number of installations over the last decades. The use of ground source heat pump (GSHP) and groundwater heat pump (GWHP) systems results in local temperature anomalies (cold or heat plumes). Since groundwater is used in many countries as source for drinking water a balance between its use and protection has to be found. Therefore, to avoid detrimental environmental impacts it is necessary to define groundwater temperature limits for heating and cooling and minimum distances between such geothermal systems. The aim of the present study is to provide a comprehensive overview of the current international legal status for the use of shallow geothermal energy. Therefore, an international survey was performed using a questionnaire, which was sent to more than 60 countries worldwide. The questionnaire requested information on the corresponding national legislation, temperature limits and minimum distances for GSHP and GWHP systems. The answers to the inquiry showed an extremely heterogeneous outcome. Until now national and legally binding regulations only exist in few countries such as Denmark or Sweden. However, all existing regulations show a wide range for minimum distances (5–300 m) and temperature limits for groundwater. The highest inconsistency was observed for the acceptable temperature change with 3 K in Switzerland to 11 K in France. However, most countries have no legally binding regulations or even guidelines, which highlight the urgent need for further research on the environmental impact and legal management of shallow geothermal installations.     

Low-enthalpy geothermal energy: An opportunity to meet increasing energy needs and reduce CO2 and atmospheric pollutant emissions in Piemonte,Italy

The scope for diffusion of very low-enthalpy geothermal plants in the Piemonte region of Italy, using groundwater heat pumps (GWHP), was analyzed to check environmental sustainability and the benefits in terms of reducing greenhouse gas emissions from fossil fuels. GWHP implementation seemed particularly suitable to the specific characteristics of the Piemonte plain. An important thick and productive shallow aquifer is present across the entire plain beneath the major energy users and is therefore appropriate for geothermal energy development purposes. The building stock could be adapted to heat pumps in different ways, but objective-oriented policies will be required to reach the best results in terms of environmental benefits.     

Dimensionless temperatures at the wall of an infinitely long,variable-rate,cylindrical heat source

In geothermal applications the thermal conductivity of rocks is needed, for example, to determine terrestrial heat flow, to evaluate heat losses to the surrounding formations in wells and to design borehole heat exchangers. Cylindrical probes (heaters) with a constant heat flow rate are used in boreholes or in the laboratory to obtain the thermal conductivity of formations and of cementing systems in geothermal wells. A new technique to calculate the temperature at the wall of an infinitely long, cylindrical, time-dependent heat source is presented.     

Evaluation of the performance of a centralized ground-water heat pump system in cold climate region

The aim of this study is to evaluate the performance of a centralized open-loop ground-water heat pump (GWHP) system for climate conditioning in Beijing with a cold climate in China. Thus, a long-time test was conducted on a running GWHP system for the heating season from December 2011 to March 2012. The analysis of the testing data indicates that the average heat-pump coefficient of performance (COP) and the COP of the system (COPs) are 4.27 and 2.59. The low value and large fluctuation in the range of COP are found to be caused by the heat transfixion in the aquifer and the bypass in the circulation loop. Therefore, some suggestions are proposed to improve the performance for GWHPs in the cold climate region in China.     

抽-灌井水量对耦合式地埋管井群传热性能的影响

基于多孔介质传热、传质理论以及有限长线热源模型,建立耦合式地埋管换热器井群热-渗数学模型,以原位热响应试验与现场抽水试验为验证依据。针对渤海盆地含水层,通过数值模拟探究不同抽-灌水量对地埋管井群传热性能的影响。研究表明:随着抽-灌水量的增大,地埋管井群换热能效系数增大,井群下游区域热影响范围扩大。在制冷与供热工况下,井孔E7所在细砂层佩克莱特数(Pe)与单位埋深换热变换量Δq关系曲线均呈高斯函数分布。基于所建耦合式地埋管井群物理模型,抽-灌水量推荐范围为400~600 m3/d。