独立双埋管太阳能辅助土壤源热泵系统模型建立与影响因素分析

太阳能辅助土壤源热泵复合系统是严寒寒冷地区实施清洁供能的重要手段之一。在该系统中,太阳能集/蓄热系统与土壤源热泵系统有不同的连接方式和运行模式,太阳能系统的运行时间直接影响土壤的热恢复程度。本文基于TRNSYS平台建立了可全年进行蓄热的太阳能辅助土壤源热泵复合系统,提出了独立双埋管土壤蓄热器模拟计算方法,并与现场测试数据进行了对比验证。基于大连市公共建筑实际工程,通过正交试验设计及TRNSYS模拟全面研究了系统运行参数,得到对系统运行能耗与土壤温度变化率有重要影响的运行参数并分析了其影响规律。结果表明：系统运行能耗与冬季热泵供水温度、负荷侧水流量、土壤侧水流量均呈正相关,与夏季热泵供水温度呈负相关;当累计供热供冷量比为1.31时,系统运行能耗与蓄热启动温度呈负相关;当累计供热供冷量比为2.32时,与蓄热启动温度为正相关;当累计供热供冷量比为1.77时且蓄热启动温度为35℃时,系统运行能耗最低。土壤温度变化率与蓄热启动温度呈负相关。应根据系统累计供热供冷量比来相应调节太阳能系统运行时间和运行参数。     

Cooling machine with integrated cold storage

The use of thermal solar energy systems in combination with thermal driven sorption chillers for climatisation gains increasing influence. For solar assisted cooling a backup system is necessary for times when no solar energy is available. Absorption chillers driven by a combination of thermal collectors and conventional furnaces, which supply the driving heat in times of no insolation, suffer from an abrupt drop of the system efficiency (COP) during the operation change. This drop in COP can be avoided by installing a combined heat buffer and storage feature. Various possibilities of heat storage features are compared. An experimental setup of a high-efficient absorption chiller which facilitates the supply of a constant load of coldness at constantly high COP in spite of periodically available driving heat is presented.     

膜蒸馏技术在溶液蓄能中的应用

本文以太阳能热利用和蓄能技术为研究背景,提出了一种基于膜蒸馏的太阳能溶液蓄能模式。采用疏水性聚偏氟乙烯中空纤维膜为膜蒸馏材料,基于膜蒸馏常温操作、小温差大传热面积的特点,利用膜材料微观上的高比表面积和单位体积的高接触面积为载体,选取50%溴化锂溶液为工质,以减压膜蒸馏的方式进行溶液浓缩和潜能存储,浓缩后的溶液可作为吸收式热力系统的工质。为此,针对50%的溴化锂溶液进行了减压膜蒸馏实验,对不同溶液温度、溶液流量在不同真空度下进行减压膜蒸馏实验,得到了3组实验数据。根据实验结果,对膜蒸馏式溶液蓄能系统进行分析,结果表明:蓄能密度可以达到245 kJ/kg,单位面积的膜组件可以产生0.27~0.40 kW的蓄能量,膜蒸馏式溶液蓄能为太阳能利用、吸收式热力系统和蓄能技术提供了一种新的应用方法和途径。     

Long-term heat storage with NaOH

To reach high solar energy fractions for building heat supply, several seasonal thermal storage techniques have been developed and tested so far. Besides ground storage techniques, thermo-chemical techniques with high heat storage capacity and virtually no heat losses in the storage state are most promising. This paper deals with closed sorption systems and focuses on the concept with sodium hydroxide (NaOH)-water as the working pair. In an experimental prototype system setup, vapor pressure and boiling temperatures of highly concentrated sodium lye, as well as heat charge and discharge processes of the storage under low-pressure conditions were analyzed or verified. The storage capacity is limited by the temperature levels of the produced heat and by the solidification of the NaOH lye. The results for the single-stage prototype show that for charging the storage, solar heat input at 150 °C is needed, and that, compared to conventional water storage, the system-volume-related heat capacity could be increased by a factor of 6 for low-temperature space heating (40 °C) and by a factor of 3 for domestic hot water supply (65-70 °C). Future systems shall be built as a double-stage system in one integral vacuum container, containing solution tanks, heat exchangers, piping, and pumps.     

Conditionnements thermiques par fluide intermédiaire et accumulation d'énergie latente

As a result of direct automation of the industrial refrigerating plants the efficiency is generally reduced by: (1) not limiting the peaks of refrigeration demand; (2) not profiting by the permissible temperature variations of the stored goods; (3) allowing unstable cycles of production and distribution. From this ascertainment the authors investigate the advantages of the different forms of storing thermal energy.The conventional thermal energy storage methods are compared such as: (1) the most popular sensible heat storage by means of water or chilled water tank: (2) the storage below freezing by means of liquid solutions (salt, alcohol, glycerol, glycol…); (3) the ice accumulation systems; (4) the eutectic-plate systems. Moreover, temperature fluctuations of the stored goods in a cold store are contemplated as a posible method of storing sensible heat, if moderate (4K for frozen and 2K for fresh goods).The above-mentioned methods, using either sensible or latent heat, are compared in terms of: utilization temperature, accumulation temperature range, and storage capacity per unit mass and unit volume. Loading and unloading rates of the storage device are also significant characteristics.The development of new storage methods are then investigated mainly in respect of energy savings in the field of agro-industries requiring both refrigeration and heating. (1) The accumulation of warm water, using either electric supply during low-fare periods, or heat pumps associated to heat rejection recovery of refrigerating plants, or any combination of both sources; (2) the latent heat accumulation which allows an important space saving compared to sensible heat accumulation.The most important recent improvements are mentioned: (1) physico-chemical (supercooling, non-reversibility of the change-of-phase process, crystallizing rate and heterogeneous crystallization); (2) heat exchange problems; (3) technological constraints; (4) financial amortization.As an illustration of the advantages of heat storage, the authors present a possible application for slaughter houses aiming at energy savings by means of: (1) heat recovery from refrigerant condensation for preheating of process water, with or without thermodynamical amplification (heat pump); (2) optimization of the running cycles of the compressors and adjustment of condensing and evaporating temperature levels. The example of a 10,000 t/year slaughterhouse is presented where an eutectic accumulation device is included in the glycol-water distribution system, allowing for the transfer of a 1250 kWh refrigeration capacity from peak to low level demand periods, with a reduced volume of 25 m³.As a conclusion, the authors review the main types of application of heat storage.     

Conditionnements thermiques par fluide intermédiaire et accumulation d'énergie latenteThermal conditioning through intermediary fluid and latent power storage

As a result of direct automation of the industrial refrigerating plants the efficiency is generally reduced by: (1) not limiting the peaks of refrigeration demand; (2) not profiting by the permissible temperature variations of the stored goods; (3) allowing unstable cycles of production and distribution. From this ascertainment the authors investigate the advantages of the different forms of storing thermal energy.The conventional thermal energy storage methods are compared such as: (1) the most popular sensible heat storage by means of water or chilled water tank: (2) the storage below freezing by means of liquid solutions (salt, alcohol, glycerol, glycol…); (3) the ice accumulation systems; (4) the eutectic-plate systems. Moreover, temperature fluctuations of the stored goods in a cold store are contemplated as a posible method of storing sensible heat, if moderate (4K for frozen and 2K for fresh goods).The above-mentioned methods, using either sensible or latent heat, are compared in terms of: utilization temperature, accumulation temperature range, and storage capacity per unit mass and unit volume. Loading and unloading rates of the storage device are also significant characteristics.The development of new storage methods are then investigated mainly in respect of energy savings in the field of agro-industries requiring both refrigeration and heating. (1) The accumulation of warm water, using either electric supply during low-fare periods, or heat pumps associated to heat rejection recovery of refrigerating plants, or any combination of both sources; (2) the latent heat accumulation which allows an important space saving compared to sensible heat accumulation.The most important recent improvements are mentioned: (1) physico-chemical (supercooling, non-reversibility of the change-of-phase process, crystallizing rate and heterogeneous crystallization); (2) heat exchange problems; (3) technological constraints; (4) financial amortization.As an illustration of the advantages of heat storage, the authors present a possible application for slaughter houses aiming at energy savings by means of: (1) heat recovery from refrigerant condensation for preheating of process water, with or without thermodynamical amplification (heat pump); (2) optimization of the running cycles of the compressors and adjustment of condensing and evaporating temperature levels. The example of a 10,000 t/year slaughterhouse is presented where an eutectic accumulation device is included in the glycol-water distribution system, allowing for the transfer of a 1250 kWh refrigeration capacity from peak to low level demand periods, with a reduced volume of 25 m³.As a conclusion, the authors review the main types of application of heat storage.     

Numerical simulation of an advanced energy storage system using H2O–LiBr as working fluid, Part 1: System design and modeling

The advanced energy storage technology proposed and patented by authors can be applied for cooling, heating, dehumidifying, combined cooling and heating, and so on. It is also called the variable mass energy transformation and storage (VMETS) technology in which the masses in one or two storage tanks change continuously during the energy charging and discharging processes. This paper presents an advanced energy storage system using aqueous lithium bromide (H₂O–LiBr) as working fluid. As one of VMETS systems, this system is a closed system using two storage tanks. It is used to shift electrical load and store energy for cooling, heating or combined cooling and heating. It is environmental friendly because the water is used as refrigerant in the system. Its working principle and process of energy transformation and storage are totally different from those of the traditional thermal energy storage (TES) systems. The electric energy in off-peak time is mostly transformed into the chemical potential of the working fluid and stored in the system firstly. And then the potential is transformed into cold or heat energy by absorption refrigeration or heat pump mode when the consumers need the cold or heat energy. The key to the system is to regulate the chemical potential by controlling the absorbent (LiBr) mass fraction or concentration in the working fluid with respect to time. As a result, by using a solution storage tank and a water storage tank, the energy transformation and storage can be carried out at the desirable time to shift electric load efficiently. Since the concentration of the working solution in the VMETS cycle varies continuously, the working process of the VMETS system is dynamic. As the first part of our study, the working principle and flow of the VMETS system were introduced first, and then the system dynamic models were developed. To investigate the system characteristics and performances under full-storage and partial-storage strategies, the numerical simulation will be performed in the subsequent paper. The simulation results will be very helpful for guiding the actual system and device design.     

Performance evaluation of single stand and hybrid solar water heaters: a comprehensive review

In this review, flat plate and concentrate-type solar collectors, integrated collector–storage systems, and solar water heaters combined with photovoltaic–thermal modules, solar-assisted heat pump solar water heaters, and solar water heaters using phase change materials are studied based on their thermal performance, cost, energy, and exergy efficiencies. The maximum water temperature and thermal efficiencies are enlisted to evaluate the thermal performance of the different solar water heaters. It is found that the solar water heaters’ performance is considerably improved by boosting water flow rate and tilt angle, modification of the shape and number of collectors, using wavy diffuse and electrodepositioned reflector coating, application of the corrugated absorber surface and coated absorber, use of turbulent enhancers, using thermal conductive working fluid and nanofluid, the inclusion of the water storage tank, and tank insulation. These items increase the heat transfer area and coefficient, thermal conductivity, the Reynolds and Nusselt numbers, heat transfer rate, and energy and exergy efficiencies. The evacuated tube heaters have a higher temperature compared to the collectors with a plane surface. Their thermal performance increases by using all-glass active circulation and heat pipe integration. The concentrative type of solar water heaters is superior to other solar heaters, particularly in achieving higher water temperatures. Their performance improves by using a rotating mirror concentrator. The integration of the system with energy storage components, phase change materials, or a heat pump provides a satisfactory performance over conventional solar water heaters.

Graphical abstract

Modification of solar water heaters

     

太阳能空气集热耦合地板蓄热系统热特性实验研究

提出了一种适用于被动式太阳能空气供暖的混凝土地板蓄热系统,并对该蓄热系统在寒冷地区农村住宅中的应用进行了热特性及其影响因素实验研究。讨论了该蓄热系统对室内热环境的作用,不同集热器朝向、热气流湿度及供风速度作用下地板蓄热系统的蓄放热特性。实验结果表明,太阳能空气集热耦合混凝土地板蓄热系统充分利用建筑本体结构蓄热,有效提高了太阳能供暖房间的室内温度及其稳定性。     

空气源热泵耦合太阳能及余热用于升压站供暖的研究

风电场、光伏发电站等工程的升压站,一般远离集中热源,冬季多采用“电暖气+热水器”的传统方案,能源利用效率低,增加了电能消耗,降低了项目收益。提出“空气源热泵耦合太阳能及余热”的供暖方案,为升压站提供了可靠的热源,并提高了能源利用效率,降低了运行费用。升压站内电气设备间有大量的40℃左右的排风,可以作为空气源热泵的低温热源,解决了空气源热泵低温时效率低的弊病;空气源热泵生产出热水,并设置太阳能热水器进一步提高水温满足供暖要求;设置单独的蓄热水箱适应供暖负荷变化并解决一部分生活热水需求。以北京某风电场工程为例,阐述了这一系统的优缺点以及推广的必要性和可行性。分析表明,在最冷时该系统仍可以高效、稳定的运行,投资回收期短,为寒冷地区空气源热泵的应用提供了参考依据。     

硝酸熔盐储热材料在太阳能利用中的研究进展

随着全球经济的快速发展,能源危机日渐凸显,太阳能作为可再生能源的一种,越来越受到人们的重视.因此,如何高效利用太阳能资源值得深究.熔盐具有良好的蓄热特性,在石化、电池及冶金行业中发挥着很大的作用,尤其可以作为传热蓄热介质应用于太阳能热发电和太阳能制氢中.其中硝酸盐的特性较为适合用于熔盐储热材料.主要针对硝酸熔融盐体系,一是介绍了硝酸熔融盐体系在太阳能方面的应用,二是介绍了国内外学者对此体系的物化性质研究,如工作温度范围、热力学性质及热稳定性等.通过对比,总结了不同混合熔融盐各项性能的异同.指出了硝酸熔融盐性能深入研究的方向,为硝酸熔盐在能源开发利用和环境保护等方面发挥更重要的作用提供了重要参考.     

Comparison of mechanical cryocoolers versus stored cryogens for balloon-borne observations

This study examines the relative mass required in the use of stored cryogens and mechanical cryocoolers, for cooling of detectors and optics in stratospheric-balloon—borne observatories. Lofted mass per unit heat removed from a cryogenic instrument is calculated, as a function of temperature, for three cooling approaches: (a) the use of stored cryogens; (b) use of an acoustic-Stirling (“pulse tube”) mechanical cryocooler powered by electric storage batteries; and (c) the same cryocooler with solar-electric energy collection partially or fully replacing storage batteries. For the latter case, the mission duration at which the systems masses are equal is also found. Principal conclusions are (1) stored cryogens can provide cooling for lower mass than storage-battery—operated cryocoolers over most of the temperature range considered, but the difference is not large; (2) solar-conversion systems can be the lower-mass option at higher temperature, but the mission duration for equal mass increases rapidly below ∼30 K.     

Hybrid Energy Harvesters: Toward Sustainable Energy Harvesting

Recently, sustainable green energy harvesting systems have been receiving great attention for their potential use in self‐powered smart wireless sensor network (WSN) systems. In particular, though the developed WSN systems are able to advance public good, very high and long‐term budgets will be required in order to use them to supply electrical energy through temporary batteries or connecting power cables. This report summarizes recent significant progress in the development of hybrid nanogenerators for a sustainable energy harvesting system that use natural and artificial energies such as solar, wind, wave, heat, machine vibration, and automobile noise. It starts with a brief introduction of energy harvesting systems, and then summarizes the different hybrid energy harvesting systems: integration of mechanical and photovoltaic energy harvesters, integration of mechanical and thermal energy harvesters, integration of thermal and photovoltaic energy harvesters, and others. In terms of the reported hybrid nanogenerators, a systematic summary of their structures, working mechanisms, and output performances is provided. Specifically, electromagnetic induction, triboelectric, piezoelectric, photovoltaic, thermoelectric, and pyroelectric effects are reviewed on the basis of the individual and hybrid power performances of hybrid nanogenerators and their practical applications with various device designs. Finally, the perspectives on and challenges in developing high performance and sustainable hybrid nanogenerator systems are presented.     

Decoupled Solar Energy Storage and Dark Photocatalysis in a 3D Metal–Organic Framework

Materials enabling solar energy conversion and long-term storage for readily available electrical and chemical energy are key for off-grid energy distribution. Herein, the specific confinement of a rhenium coordination complex in a metal–organic framework (MOF) unlocks a unique electron accumulating property under visible-light irradiation. About 15 C g_MOF⁻¹ of electric charges can be concentrated and stored for over four weeks without loss. Decoupled, on-demand discharge for electrochemical reactions and H₂ evolution catalysis is shown and light-driven recharging can be conducted for >10 cycles with ≈90% of the initial charging capacity retained. Experimental investigations and theoretical calculations link electron trapping to MOF-induced geometry constraints as well as the coordination environment of the Re-center, highlighting the key role of MOF confinement on molecular guests. This study serves as the seminal report on 3D porous colloids achieving photoaccumulation of long-lived electrons, unlocking dark photocatalysis, and a path toward solar capacitor and solar battery systems.     

基于太阳能热化学的分布式供能系统热力学性能及碳排放分析

分布式供能系统临近用户,具有灵活消纳可再生能源的优势。集成太阳能与清洁燃料互补的分布式供能系统,旨在实现太阳能与燃料的高效互补利用。提出了基于太阳能热化学的分布式供能系统,该系统集成了太阳能热化学转化与分布式冷热电联供系统,将太阳能与甲醇以热化学的形式进行源头互补,把太阳能转化为合成气燃料化学能,进而通过内燃机发电机组和余热回收单元输出冷、热、电产品,以满足用户的负荷需求。通过数值计算的方法,对所集成的系统开展了热力学性能及CO₂排放性能分析,研究了设计工况及变工况下运行性能,结果表明所集成的太阳能与燃料热化学互补供能系统具有显著的节能减排优势。     

化学吸附储热技术的研究现状及进展

化学吸附储热技术具有储热密度高、长时间储热几乎无热损失且可以实现冷热的复合储存等优点,在太阳能等可再生能源的有效利用和中低温余热/废热的回收利用中具有良好的应用前景,已成为国内外的研究热点。本文针对无机盐与水蒸气的水合反应和金属氯化物等与氨气的络合反应两类化学吸附储热方式进行了系统综述,归纳和总结了化学吸附储热技术的研究现状以及最新进展。对化学吸附储热材料进行了概括,并且对典型的化学反应器以及吸附储热装置进行了回顾。基于研究现状的分析,阐述了化学吸附储热当前研究中存在的问题,并进一步指出了该技术未来需要克服的问题和研究方向。     

纳米材料改善硝酸熔盐传蓄热性能的研究进展EI北大核心CSCD

聚光式太阳能热发电是解决能源和环境矛盾的理想途径,传热蓄热技术是光热发电的重要环节,在此需要解决的关键问题是传热蓄热介质。熔盐作为储蓄热介质具有明显优势。国内外运行的光热电站中大多使用二元硝酸熔盐(Solar salt)与三元硝酸熔盐(Hitec),但二者传蓄热性能均欠佳,影响了太阳能的利用效率。纳米材料的独特空间结构,使其具有优异的导热性能、良好的稳定性等,将其作为添加剂引入到硝酸熔盐体系中,有望改善材料的传热蓄热等热物性能,进而提高太阳能光热利用的效率,降低发电成本。本文综述了纳米金属粒子、纳米金属氧化物、纳米碳材料和其他无机纳米材料作为添加剂掺杂到硝酸熔盐体系中的相关研究,论述了改性后熔盐热物性的变化并探讨了作用机理,以期为制备优异热性能的储能熔盐提供参考。未来的研究可重点关注热物性测试、传热机理、构效关系和工业化中试,将具有优异的传蓄热性能的硝酸熔盐应用在太阳能光热发电领域,在清洁能源开发利用方面发挥更重要的作用。     

天然气在空调供热中的应用分析

天然气是清洁的一次能源.在空调供热中推广应用天然气可减少因空调供热引起的电网峰谷差,符合我国的能源和环境保护政策.本文介绍了几种以天然气为一次能源的空调供热系统,包括燃气溴化锂吸收式热泵、燃气机制冷空调样机及其测试性能和冷热电联供系统(CCHP).     

新型布雷登塔式太阳能热发电系统

太阳能热发电通常以水工质吸热作为第1代,以熔盐吸热作为第2代,以空气、超临界二氧化碳或固体粒子作为介质的布雷登循环系统称为第3代太阳能热发电系统。通过采用空气或陶瓷粒子作为吸热介质,采用干热存储介质（如耐火砖和陶瓷材料等）进行规模化储热,能提高系统效率和降低成本,系统的储热能力可保证电站在任何时候都按照电网调度要求发电。采用标准化模块设计,通过工厂化制作,使电站设计、设备生产、安装、调试和运行都大为简便,储存的热量可用于食品加工、干燥、农业应用等。根据美国能源部的研究,具有储热功能的模块配备小型燃气型透平可实现快速启停,改善电网电压和频率质量。