Performance analysis of deep borehole heat exchangers for decarbonization of heating systems

Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.

Experiments Using Capillary Mat as Ground Heat Exchanger for Ground Source Heat Pump Heating Application

The cooling and heating of spaces are among the largest sources for household’s energy demand. Ground Source Heat Pump (GSHP) is a promising technology to reduce the energy for cooling and heating purposes. However, the major obstacle hindering the utilization of this technology is the high initial cost, especially for the installation of ground coupled heat exchanger. The horizontal closed-loop system offers lower installation cost, as it requires no vertical borehole construction. Instead, the heat exchangers can be installed in shallow trenches that may be excavated, by small excavator or even by human labor. This paper presents the comparison of two different heat exchangers, namely, the capillary mat and the widely used slinky pipe. Both heat exchangers are connected to a heat pump, where continuous heating tests were carried out for 165 hours (~7 days) for each configuration. The purpose of this research is to show the performance of capillary mat in comparison to slinky pipe. Despite during the entire test for capillary mat required 6% higher electricity consumption, compared to slinky heat exchanger, the results still suggest the potential use of capillary mat as alternative to slinky heat exchanger. Additionally, the results also highlight the high hydraulic resistance of installed capillary mat heat exchangers may become the major disadvantage of the capillary mat.

Strong self-flushing technique for heat exchanger of sewage source heat pump system

To better remove the contamination on the surface of a heat-exchanger in urban sewage source heat pump system （USSHPS）, this paper analyzes the feasibility of strong self-flushing on the basis of experiments and presents a new on-line self-flushing technique, which alternately flushes part of heat transfer tubes. In addition, operation principles and the structure of the new heat-exchanger are introduced and the feasible economi- cal and technological cleaning plans are given by design calculation and scheme comparison. The result shows that keeping each tube washed for one minute with 5 m/s, the operating cost is lower than ￥5 and when one flushing pump ahemately flushes 10-20 heat exchangers, the saved costs of flushing 10 tubes alternately are over 4 times of the increased costs.

Research on ground heat exchanger of Ground Source Heat Pump technique

Ground Source Heat Pump technique and its operating principle are described in this paper. Ground heat exchanger is the key technique of ground source heat pump and its patterns are discussed. Software is helpful to design ground heat exchanger. A project of Chinese Ground Source Heat Pump is introduced and its market is more and more extensive.

Arrangement Strategy of Ground Heat Exchanger with Groundwater

The orientation strategy of side pipe and the heat transfer performance of six ground heat exchangers(GHEs) were optimized by numerical simulation,with soil being treated as a porous medium.An experiment on the heat transfer of four GHEs was carried out in 2010.Results indicate that the velocity field is disturbed by GHEs.The optimal orientation strategy of side pipe is that the upward pipe is located upstream and the downward pipe downstream.The space between GHEs should be appropriately adjusted,depending on the direction and flow velocity.Groups of GHEs should be installed perpendicular to the mainstream in a single row,but if the acreage does not meet the requirements,GHEs should be installed in staggered multiple rows.Fewer GHEs parallel to the mainstream strengthen the heat transfer.Moreover,numerical results agree well with the test data,with the maximum relative error being less than 7.7%.

Numerical Simulation of Heat Transfer Characteristics of Horizontal Ground Heat Exchanger in Frozen Soil Layer

A simplified numerical model of heat transfer characteristics of horizontal ground heat exchanger (GHE) in the frozen soil layer is presented and the steady-state distribution of temperature field is simulated. Numerical results show that the frozen depth mainly depends on the soil′s moisture content and ambient temperature. The heat transfer loss of horizontal GHE tends to grow with the increase of the soil′s moisture content and the decrease of ambient temperature. Backfilled materials with optimal thermal conductivity can reduce the thermal loss effectively in the frozen soil. The applicability of the Chinese national standard “Technical Code for Ground Source Heat Pump (GB 50366-2005)” is verified. For a ground source heat pump project, the feasible layout of horizontal GHE should be determined based on the integration of the soil′s structure, backfilled materials, weather data, and economic analysis.

Heat transfer analysis and experimental verification of cast heat exchanger

From the viewpoints of environmental conservation and energy efficiency,seawater-source heat pump system(SWHP) to provide district cooling and heating is applied in coastal areas.Based on the system,a heat transfer model was established for cast heat exchanger(CHE) adopted by SWHP systems.The CHE consists of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of SWHP system.An experimental study was carried out to test the validity of the model.A program was developed in VB language and the effects of inlet temperature,flow rate of the secondary refrigerant and length of CHE on the results were investigated.The results of the numerical simulation are in consistence with the experiments in both winter and summer conditions.As a result,application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment.

Research on Performance of Ground-Source Heat Pump Double U Underground Pipe Heat Exchange

This paper uses FLUENT software building the three-dimensional unsteady state model of ground source heat pump single U and double U underground pipe to study on heat exchange of underground pipe system in the condition of unsteady state long-term continuous running, analyzes the change of soil temperature filed around underground pipe and performance of underground pipe heat exchange between single U and double U pipe system. The results show that double U pipe system is better than single U system, which can improve unit depth heat exchange efficiency, reduce the number of wells and reduce the initial investment.

Experimental study on heat exchange of several types of exchangers

Aiming at the ground-coupled source heat pump that possesses the shortcomings of occupying larger land,this article studies the heat exchanged of heat exchanger in piling,and compares it with common heat exchangers buried directly. The result indicates that the heat exchanger makes the best use of structure of building,saves land,reduces the construction cost,and the heat exchanged is obviously more than exchangers buried directly. In winter condition,when W-shape pipe heat exchanger in pile foundation is 50 m deep and diameter is 800 mm,it transfers 1.2-1.3 times as large as the one of single U-shape buried directly at the flow rate of 0.6 m/s,whose borehole diameter is 300 mm. And in summer condition it does about 2.0-2.3 times as that of U-shape one.

Severe acute respiratory syndrome coronavirus 2 may cause liver injury via Na^(+)/H^(+) exchanger

The liver has many significant functions,such as detoxification,the urea cycle,gluconeogenesis,and protein synthesis.Systemic diseases,hypoxia,infections,drugs,and toxins can easily affect the liver,which is extremely sensitive to injury.Systemic infection of severe acute respiratory syndrome coronavirus 2 can cause liver damage.The primary regulator of intracellular pH in the liver is the Na+/H+exchanger(NHE).Physiologically,NHE protects hepatocytes from apoptosis by making the intracellular pH alkaline.Severe acute respiratory syndrome coronavirus 2 increases local angiotensin II levels by binding to angiotensinconverting enzyme 2.In severe cases of coronavirus disease 2019,high angiotensin II levels may cause NHE overstimulation and lipid accumulation in the liver.NHE overstimulation can lead to hepatocyte death.NHE overstimulation may trigger a cytokine storm by increasing proinflammatory cytokines in the liver.Since the release of proinflammatory cytokines such as interleukin-6 increases with NHE activation,the virus may indirectly cause an increase in fibrinogen and D-dimer levels.NHE overstimulation may cause thrombotic events and systemic damage by increasing fibrinogen levels and cytokine release.Also,NHE overstimulation causes an increase in the urea cycle while inhibiting vitamin D synthesis and gluconeogenesis in the liver.Increasing NHE3 activity leads to Na+loading,which impairs the containment and fluidity of bile acid.NHE overstimulation can change the gut microbiota composition by disrupting the structure and fluidity of bile acid,thus triggering systemic damage.Unlike other tissues,tumor necrosis factor-alpha and angiotensin II decrease NHE3 activity in the intestine.Thus,increased luminal Na+leads to diarrhea and cytokine release.Severe acute respiratory syndrome coronavirus 2-induced local and systemic damage can be improved by preventing virus-induced NHE overstimulation in the liver.

Energy saving analysis of a hybrid ground-coupled heat pump project

A hybrid ground-coupled heat pump（HGCHP）project in Nanjing,China is chosen to analyze the building energy-consumption properties in terms of different control strategies,building envelope and the terminal air-conditioning system.The HGCHP uses a supplemental heat rejecter to dissipate extra thermal energy to guarantee underground soil heat balance.The software EnergyPlus is employed to simulate the project and design the heat flow of the cooling tower and the borehole heat exchanger（BHE）.Then two feasible control strategies for the cooling tower and the borehole heat exchanger are proposed.The energy-saving potential of the building envelope is analyzed in terms of the surface color of the wall/roof.With the same terminal system,it is found that in the cooling season the heat flow of the insulated building with black wall/roof is 1.2 times more than that with white wall/roof.With the same insulated building and gray wall/roof,it is concluded that the heat pump units for a primary air fan-coil system show an annual energy consumption increase of 44.7 GJ compared with a radiant floor system.

Experimental Investigation on System with Combination of Ground-Source Heat Pump and Solar Collector

This paper presents the heating performance and energy distribution of a system with the combination of ground-source heat pump and solar collector or a solar-assisted ground-source heat pump system (SAGSHPS) by calculation and experiment.The results show that the average absolute error is less than 0.6 ℃ and the relative error is less than 5% under the pulse load when the analytical solution to the 2-D solid cylindrical source model is used for the SAGSHPS.The coefficient of performance (COP) of the SAGSHPS is 2.95-4.70.The average fluid temperature in the borehole heat exchanger can increase by 3 ℃ with the assistance of solar collector,which will improve the COP of the heat pump by approximately 10% from the experimental data.The energy contributions to the total heating load of soil,electricity and solar are 56.30%,36.87% and 6.83%,respectively.

Field evaluation of a ground-coupled heat pump in hot-summer and cold-winter regions

The experimental performance of small-sized ground-coupled heat pump (GCHP) is researched intensively. However, there are little data documenting the operation performance of existing large-sized GCHP system. We presented the actual performance measurement of a GCHP installed for apartment buildings in Wuhan, Hubei province, P. R. China. The system was constructed with a closed vertical typed ground heat exchanger with a total pipe length of 32 000 m. During one year, various operating parameters were monitored, including the outdoor temperature, the flow rate, the electrical consumption, and the water temperature. The seasonal coefficients of performances of the heat pumps and the system based on the measured data were found to be 4.01 and 2.96 in the cooling season, and 3.54 and 2.86 in the heating season, respectively. The GCHP system was more economical than the air-source room air conditioner in the energy efficiency which was increased by 29% in cooling mode and 50% in heating mode. There was an obvious heat imbalance of soil between the injection rate and the extraction rate in the residential GCHP system operation.

Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography

A miniature quad-channel optically pumped atomic magnetometer(OPM) has been developed based on the spinexchange relaxation-free(SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography(MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^(1/2), which is also good enough for MEG measurement. The vapor cell is heated to 160℃ by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.

The Quantum-Mechanical Sensitive Na/K Pump Is a Key Mechanism for the Metabolic Control of Neuronal Membrane Function

At present, there are relevant scientific materials on the cellular and molecular mechanisms of electrogenic Na/K pump function and structure, as well as on the potential- and ligand-activated ionic channels in the membrane. However, the role of electrogenic Na/K pump in regulation of semipermeable properties of cell membrane has not been elucidated yet, which is due to the fact that our knowledge about the biophysical properties of cell membrane is based on the conductive membrane theory of Hodgkin-Huxley-Katz, which is developed on internally perfused squid axon and lacks intracellular metabolism. Thus, the accumulated abundance of data on the role of G-proteins-dependent intracellular signaling system in regulation of Na/K pump activity and biophysical properties of cell membrane presumes fundamental revision of some statements of membrane theory. The aim of the present review is to briefly demonstrate our and literature data on cell hydration-induced auto-regulation of Na/K pump as well as on its role in metabolic control of semipermeable properties and excitability of neuronal membrane, which are omitted in the study of internally perfused squid axon.

感潮河段江滩湿地水体交换模拟与调控措施研究

保障湿地水体交换能力对完善湿地功能,维持湿地生态系统的健康至关重要。南京绿水湾湿地是长江江滩湿地,具备多种湿地特点,动力条件复杂。以绿水湾湿地为研究对象,通过构建二维水动力―水龄耦合数学模型,模拟了现状和不同闸、泵调控措施下各区域的水动力特征及水体交换能力。结果表明:现状工况湿地内部水面覆盖率低,水体交换能力差,大部分区域水体交换时间在7 d以上,甚至是14 d以上;建闸后虽然增加了枯季的水面覆盖率,但明显减弱了湿地内水动力,延长了各区域换水周期,换水周期大于14 d的区域明显增多;补水泵站的运用整体上缩短了大部分区域的换水周期,使得水域流速大于0.010 m/s的区域面积明显增加,换水周期大于14 d的区域面积减少。建闸蓄水后,为预防藻类暴发,需控制湿地内水体的换水周期在14 d内,结合各区域水动力和水体交换特点,提出了闸门生态调度、布置净水能力较强的挺水或沉水植物、增设补水点等调度策略。

换热站并联水泵分布式优化控制

针对现有换热站并联水泵优化算法在集中式架构下控制适应性不足的问题,本文提出了一种改进的分布式并联水泵优化算法.首先,建立了并联水泵的分布式控制系统,并对该优化问题的数学模型进行描述,在目标函数中引入自适应非线性因子;然后,设计了改进的分布式果蝇优化算法,在该算法中每台水泵的控制器仅通过与邻居控制器交互信息即可完成并联水泵的优化;并且,在嗅觉搜索阶段,使用正弦余弦策略替代赋予个体距离与方向的随机策略;最后,以两个实际换热站中不同并联水泵系统为例对算法进行仿真验证,并基于仿真结果进行性能分析.结果表明,相较于传统算法,改进的分布式果蝇优化算法能得到更优的控制策略,有着收敛速度快、稳定性好和鲁棒性强的特点;并且该算法适用于不同系统的并联水泵优化问题,具有可扩展性.在实际工程验证中相较于集中式算法,该算法在总功率和计算时间上分别平均降低了5.47%和29.90%,因此,能够满足实际换热站中对并联水泵热负荷优化分配的需求.

水-冰相变凝固换热与热泵耦合供热系统实验研究

针对河北山区农村水源不足、地源钻井成本高、太阳能不稳定、造价高、没有合适的热泵低温热源等问题,研发了水-冰相变换热器;利用水的相变潜热作为热泵的低温热源,设计了水-冰相变凝固换热与热泵耦合供热系统,搭建了实验平台,经测试平台运行稳定可靠。通过对实验数据进行分析计算,得到系统性能系数在2.87~3.42之间。研究结果可为解决河北山区农村供暖问题提供参考。

竖直单U型地埋管换热器埋管间负热阻现象的参数化研究与分析

基于Mutipole方法对竖直单U型地埋管换热器钻孔内外的耦合传热过程进行求解,在钻孔内三热阻和四热阻简化传热模型基础上,详细地分析钻孔内的复杂稳态传热过程,参数化研究埋管布置结构、回填料与岩土热物性等因素对钻孔内埋管间直接传热热阻的影响规律,揭示导致钻孔内埋管间负热阻现象的本质原因,对钻孔内热阻传热模型的工程实践应用给出参考意见。

地埋管换热系统改造项目关键技术节点施工工艺研究

天津某管业公司建筑原采用常压燃气热水锅炉供热和分体式空调供冷,现拟以浅层地热能为基础能源对原供热制冷系统进行改造,施工前首先通过现场岩土热响应试验、地下管线探测等查明施工场地岩土体结构和换热能力,掌握地下综合管线的分布,并对建筑单位冷热负荷指标校正。重点阐述地埋管换热系统施工过程的关键技术节点,即竖直换热孔钻进、下管、回填及水平管线连接等,为类似改造项目提供参考。