地下蓄能及其对地源热泵系统的作用

着重论述了地下蓄能（UTES）技术发展现状和所面临的问题，包括传热机理的研究，复杂地下环境中不稳定传热的特性以及UTES系统的控制策略等。通过地源热泵系统的竖直钻井中传热的实验和模拟计算，对蓄能的传热作用进行了分析和探讨。结果表明：蓄能改变地下蓄能体的能位，并表现为蓄能体温度和分布的变化随时间而改变。建议通过模型分析，结合实验研究进一步完善地下蓄能的研究工作，推动中国地下蓄能技术的发展。     

地下蓄能体多孔介质传热及其热湿迁移分析

蓄能技术是实现能源可再生和高效利用的一个有效途径。能量通过短期或长期蓄存,提高其综合利用率和实现能源的实时补充。地下蓄能过程是一个受岩土特征影响的复杂多变的传热过程。着重论述地下蓄能技术发展状况和面临的研究问题,并通过模型分析和模拟计算对多孔特征下蓄能体传热作用进行了分析和探讨,考察了几种典型工况下的温度分布。     

岩土地质结构热物性对地下蓄能影响分析

为了提升地下蓄热能力,探讨不同岩土地质结构材料对地下蓄能效果的影响。采用地下换热器群的多热源传热数值计算方法,分析了地下岩土地质结构热物性参数对地下蓄能岩土温变性和温度分布状态变化的影响,明确有关因素的影响程度和敏感度。结果表明地下岩土蓄能体的导热系数和体积比热对地下蓄能效果具有显著的敏感性,分别决定了蓄入周期内能量的扩散能力和存储能力。研究结果还表明,热物性对蓄能的能量品位具有显著的影响作用;而且,由于其明显的影响程度,导致热物性参数偏差将对地下换热器系统设计产生直接的影响。     

海水抽水蓄能技术在海岛供电中的应用探讨

电力供应的滞后制约了海岛及其周边海域的开发。海水抽水蓄能技术以海洋作为低位水库,降低工程建设成本,可解决传统抽水蓄能技术对淡水资源过度依赖和环境破坏等问题。研究表明,海水抽水蓄能与风能、太阳能、海洋能等可再生能源组成联合发电系统具有可行性,能够实现海岛可再生能源的大规模开发和利用。介绍了海岛供电系统的现状,阐述了海水抽水蓄能技术的工作原理和应用现状,分析了技术应用中存在的问题和挑战,并对海水抽水蓄能技术在海岛供电系统中的应用前景作了展望。     

压缩空气地下咸水含水层储能技术

能源危机和温室效应促进了可再生能源的利用,储能技术是解决太阳能、风能波动问题的重要手段。压缩空气储能（Compressed Air Energy Storage, CAES）技术是仅次于抽水蓄能的第二大蓄能技术。目前CAES多是通过洞穴实现,其主要缺点是对地质要求较高,合适的洞穴数量有限,为扩大其应用,可使用地下咸水含水层作为储层。本文介绍了CAES电站的工作原理、优缺点及各国的发展现状,并分析了利用地下咸水含水层进行压缩空气储能的可行性、优点及一些问题与技术方法,如储层内残余烃的影响、氧化与腐蚀作用、颗粒的影响及缓冲气的选择,表明含水层CAES将是拓宽CAES应用的重要途径。     

水风光能源互补形式的研究探讨

能源是人类社会发展的必备需要,人类发展史就是一部能源发展史.在"碳达峰"和"碳中和"战略指引下,中国的能源生产形势和发展路径将会发生一次革命性的变化.如何有序减碳,实现碳排放的既定目标,又保证我国的能源安全,不影响经济发展.现在电力产生过程不生产碳的能源就是水、风和光等主要的清洁能源.从技术可开发量上看,三种能源如果实现大规模开发,确实可以满足我国的能源需求.但是众所周知,风光能源的间隙性和随机性确实对电力系统的安全运行构成了威胁.如何实现风光能源的大规模应用,同时电网安全运行就成为了一个重大能源研究课题.本文对目前通过实现水风光蓄互补对新能源接入进行了探讨,包括常规水电和风光新能源互补,抽水蓄能和风光新能源互补,蓄能大泵和新能源互补.这三种形式均是业界正在研究推广的模式.为将来的风光新能源大规模接入提供参考.     

应用于道路融雪中太阳能集热蓄能和地下换热器影响作用研究

针对新型道路融雪化冰技术的太阳能路面集热和地下蓄能过程进行模型分析,研究逐年长期地能利用和热泵循环过程的基本性能。研究表明:运行5a后,有、无蓄能过程的热泵系统间COP相差达10%。其中,非蓄能条件下,地下均衡温度降低,热泵耗能增加,COP降低;采用集热蓄能,补偿地下热量缺失,可以达到地温恢复或增高,提升运行效能。此外,比较四孔和七孔地下换热器设置规模,两者间的流体最低温度相差2倍以上,孔数规模对地下温度、吸热量和热泵效能影响较大。因此,在地下换热器系统设计中,即要考虑孔数规模的经济性,又要保证热力性能。     

降低前滩能源大蓄能罐热转冷的运行成本

分布式能源中心配有蓄能罐,其作用是利用电网峰谷用电差,夜间进行蓄能,白天进行供能,实现削峰填谷,提高能源利用率,对缓解电力紧张和能源事业的健康发展具有重要意义。蓄能罐使用中蓄热转换蓄冷,需要耗费大量电量,导致大多数分布式能源利用大蓄能罐蓄冷。锅炉或溴化锂机组直接供热,放弃利用大蓄能罐同时蓄热蓄冷功能。讨论蓄能罐蓄热转蓄冷的使用成本,利用合理方法降低蓄热蓄冷互相转换的成本。     

物理储能技术的市场现状及发展前景

作为可再生能源并网的关键技术,可再生能源的高速发展也带动了储能产业的发展和成熟。物理储能技术,发展历史长,技术较为成熟,部分已实现商业化运作;以抽水蓄能为代表,是电网调峰的主力,也在储能市场容量中占据着绝对份额。但无论是传统抽水蓄能,还是压缩空气储能都对环境、地理地质条件有较高的要求,极大地制约了这些技术的普遍推广和应用。因此物理储能也经历着应用模式的变革、传统技术向新兴技术转化的过程。虽然抽水蓄能、压缩空气储能和飞轮储能三种物理储能技术在原理、应用领域、安装容量以及未来发展趋势上各不相同,但作为战略新兴技术,都需要技术的突破、政策和资金的支持以及更多的市场应用机会。     

Current application situation and development prospect of physical energy storage technologies

作为可再生能源并网的关键技术,可再生能源的高速发展也带动了储能产业的发展和成熟。物理储能技术,发展历史长,技术较为成熟,部分已实现商业化运作;以抽水蓄能为代表,是电网调峰的主力,也在储能市场容量中占据着绝对份额。但无论是传统抽水蓄能,还是压缩空气储能都对环境、地理地质条件有较高的要求,极大地制约了这些技术的普遍推广和应用。因此物理储能也经历着应用模式的变革、传统技术向新兴技术转化的过程。虽然抽水蓄能、压缩空气储能和飞轮储能三种物理储能技术在原理、应用领域、安装容量以及未来发展趋势上各不相同, 但作为战略新兴技术,都需要技术的突破、政策和资金的支持以及更多的市场应用机会。     

Review of development from GSHP to UTES in China and other countries

Energy storage technologies (EST) facilitate the efficient utilization of renewable energy sources and energy conservation, and they are expected to be more prevalent in the future. There is a great potential to substitute the use of EST for burning of fossil fuels by using stored heat that would otherwise be wasted and using renewable generation resources. These energy sources can be used more effectively through the addition of short- or long-term energy storage, even to the seasonal thermal energy storage. Underground thermal energy storage (UTES) is one form of EST, and perhaps the most frequently used storage technology in North America and Europe. Gradually it is growing as the application of ground source heat pump (GSHP) with UTES in China. But UTES systems involve complicated unsteady processes that include energy rejection, accumulation, preservation and extraction. This paper reviewed the progress of UTES companioning with GSHP worldwide, and surveyed the development of GSHP and the origination of UTES, especially as to soil/rock UTES. Meanwhile, the basic proposal for development in the future to supply a gap in the field of UTES in China was presented. A coming work should aim to more researching basic problems during the demonstration application, such as investigation of mechanisms, characteristics and performance of the unsteady and transient heat transfer in a complex underground environment, and control strategies of the UTES system. These problems will strengthen theoretical and practical understanding and facilitate more extensive application of UTES in China.     

Optimization for operating modes based on simulation of seasonal underground thermal energy storage

A simulation was performed, which concerned the feasibility of seasonal underground thermal energy storage (UTES) in Tianjin, China. The investigated system consisted of 8 boreholes. In summer, residual solar thermal energy was emitted into the soil surrounding the borehole heat exchangers through which the stored energy was extracted in winter with a ground coupled heat pump (GCHP) to provide a proper heating temperature. A simulation study was performed to study the influence of system operation modes on thermal recovery based on the experimental data of a GCHP system, local meteorological conditions and soil properties in Tianjin. The results indicate a thermal recovery ratio of less than 67% and different temperature distributions under three modes. Finally, an operation mode was suggested based on both lower loss and better thermal recovery in the UTES.     

Combination of ground source heat pumps with chemical dehumidification of air

In the present paper the possible synergies provided by the combination of an underground thermal energy storage (UTES) system with a desiccant based air handling unit (AHU) are analysed. Differently from the conventional solutions, the summer humidity control is obtained here by chemical dehumidification of the ventilation airstream performed by liquid desiccants in a packed column. Being the water temperature of the boreholes heat exchangers generally suitable to meet the sensible load without any integration with the chillers, the plant can operate in a complete free-cooling mode. In winter, the main benefits are due to the higher temperature level at which the UTES works and to the AHU configuration allowing sensible and latent heat recovery. For the same reasons, the required UTES size is sensibly smaller, reducing in this way not only the operation but above all the investment costs. The UTES system competitiveness is then increased. The described solution is investigated by a computer simulation referring to a modern office building in the climate of northern Italy and its performance has been compared to a traditional HVAC plant and to a traditional ground source heat pump (GSHP) system. Finally, some economic evaluations are reported, showing the competitiveness of the proposed configuration.     

Experiment and simulation of temperature characteristics of intermittently-controlled ground heat exchanges

Because of poor heat transfer coefficients of soil/rock, ground source heat pumps (GSHP) or underground thermal energy storage (UTES) systems always occupy a large area and need many ground heat exchangers. This initial energy investment is so heavy that it cannot be used on a large-scale. Intermittent operation can reduce the extreme temperatures around the ground heat exchangers (GHEs) and keep the temperature in reasonable range. The aim of this study is to implement an experiment and develop a dynamic model of hydronic heating systems of GSHP in order to get a more fair comparison of energy efficiency between continuously controlled and intermittently controlled systems. Factors such as thermal inertia, temperature levels and lag time are also considered to see how they affect the efficiency. It is shown that temperature variation is related to the intermittent period and that intermittence prolongs the heat transfer without reaching at an utmost temperature (operation limitation). An effectively controlled intermittent process can optimize the capacity of heat exchange units so as to achieve better application of the ground energy. Additionally, the intermittent control can decrease the number of GHEs of GSHP and UTES systems and keep better working conditions.     

Energy analysis and modeling of a solar assisted house heating system with a heat pump and an underground energy storage tank

An analytical model is presented and analyzed to predict the long term performance of a solar assisted house heating system with a heat pump and an underground spherical thermal energy storage tank. The system under investigation consists of a house, a heat pump, solar collectors and a storage tank. The present analytical model is based on a proper coupling of the individual energy models for the house, the heat pump, useful solar energy gain, and the transient heat transfer problem for the thermal energy storage tank. The transient heat transfer problem outside the energy storage tank is solved using a similarity transformation and Duhamel’s superposition principle. A computer code based on the present model is used to compute the performance parameters for the system under investigation. Results from the present study indicate that an operational time span of 5–7 years will be necessary before the system under investigation can attain an annually periodic operating condition. Results also indicate a decrease in the annually minimum value of the storage tank temperature with a decrease in the energy storage tank size and/or solar collector area.     

Optimization for operating modes based on simulation of seasonal underground thermal energy storage

A simulation was performed, which concerned the feasibility of seasonal underground thermal energy storage (UTES) in Tianjin, China. The investigated system consisted of 8 boreholes. In summer, residual solar thermal energy was emitted into the soil surrounding the borehole heat exchangers through which the stored energy was extracted in winter with a ground coupled heat pump (GCHP) to provide a proper heating temperature. A simulation study was performed to study the influence of system operation modes on thermal recovery based on the experimental data of a GCHP system, local meteorological conditions and soil properties in Tianjin. The results indicate a thermal recovery ratio of less than 67% and different temperature distributions under three modes. Finally, an operation mode was suggested based on both lower loss and better thermal recovery in the UTES. __________ Translated from Journal of North China Electric Power University, 2007, 34(2): 74–77 [译自: 华北电力大学学报]     

Experimental research on thermal characteristics of PCM thermal energy storage units

To explore thermal management integration in electric vehicles (EVs), a phase change materials (PCMs) thermal energy storage unit using flat tubes and corrugated fins is designed. The investigation focuses on the thermal characteristics of the PCM unit, such as the temperature variation, heat capacity, and heat transfer time, etc. Meanwhile, the heat storage and release process will be influenced by different inlet temperature, liquid flow rate, melting point of the PCM, and the combination order of the units. Under the same inlet temperature and flow rate condition, the PCM unit with higher melting point enters the latent heat storage stage slowly and enters the phase change melting release stage quickly. Furthermore, the heat storage and release rates increase with increasing liquid flow rates, but the effects are diminishing in the middle and later periods. The multiple PCM units with different melting temperatures are cascaded to help recycle low-grade heat energy with different temperature classes and exhibit well heat storage and release rates.     

Solar water heaters with phase change material thermal energy storage medium: A review

Latent heat thermal energy storage is one of the most efficient ways to store thermal energy for heating water by energy received from sun. This paper summarizes the investigation and analysis of thermal energy storage incorporating with and without PCM for use in solar water heaters. The relative studies are classified on the basis of type of collector and the type of storage used i.e. sensible or latent. A thorough literature investigation into the use of phase change material (PCM) in solar water heating has been considered. It has been demonstrated that for a better thermal performance of solar water heater a phase change material with high latent heat and with large surface area for heat transfer is required.     

Review of thermal energy storage for air conditioning systems

Thermal energy storage is very important to eradicate the discrepancy between energy supply and energy demand and to improve the energy efficiency of solar energy systems. Latent heat thermal energy storage (LHTES) is more useful than sensible energy storage due to the high storage capacity per unit volume/mass at nearly constant temperatures. This review presents the previous works on thermal energy storage used for air conditioning systems and the application of phase change materials (PCMs) in different parts of the air conditioning networks, air distribution network, chilled water network, microencapsulated slurries, thermal power and heat rejection of the absorption cooling. Recently, researchers studied the heat transfer enhancement of the thermal energy storage with PCMs because most phase change materials have low thermal conductivity, which causes a long time for charging and discharging process. It is expected that the design of latent heat thermal energy storage will reduce the cost and the volume of air conditioning systems and networks.     

Heat pipe based cold energy storage systems for datacenter energy conservation

In the present paper, design and economics of the novel type of thermal control system for datacenter using heat pipe based cold energy storage has been proposed and discussed. Two types of cold energy storage system namely: ice storage system and cold water storage system are explained and sized for datacenter with heat output capacity of 8800 kW. Basically, the cold energy storage will help to reduce the chiller running time that will save electricity related cost and decrease greenhouse gas emissions resulting from the electricity generation from non-renewable sources. The proposed cold energy storage system can be retrofit or connected in the existing datacenter facilities without major design changes. Out of the two proposed systems, ice based cold energy storage system is mainly recommended for datacenters which are located in very cold locations and therefore can offer long term seasonal storage of cold energy within reasonable cost. One of the potential application domains for ice based cold energy storage system using heat pipes is the emergency backup system for datacenter. Water based cold energy storage system provides more compact size with short term storage (hours to days) and is potential for datacenters located in areas with yearly average temperature below the permissible cooling water temperature (∼25 °C). The aforesaid cold energy storage systems were sized on the basis of metrological conditions in Poughkeepsie, New York. As an outcome of the thermal and cost analysis, water based cold energy storage system with cooling capability to handle 60% of datacenter yearly heat load will provide an optimum system size with minimum payback period of 3.5 years. Water based cold energy storage system using heat pipes can be essentially used as precooler for chiller. Preliminary results obtained from the experimental system to test the capability of heat pipe based cold energy storage system have provided satisfactory outcomes and validated the proposed system concept.