Research on Operation Optimization of Heating System Based on Electric Storage Coupled Solar Energy and Air Source Heat Pump

For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency.In this paper,four cities in three climatic regions in China were selected,namely Nanjing in the hot summer and cold winter region,Tianjin in the cold region,Shenyang and Harbin in the severe cold winter region.The levelized cost of heat(LCOH)was used as the economic evaluation index,and the energy consumption and emissions of different pollutants were analyzed.TRNSYS software was used to simulate and analyze the system performance.The Hooke-Jeeves optimization algorithm and GenOpt software were used to optimize the system parameters.The results showed that ECSA systemhad an excellent operation effect in cold region and hot summer and cold winter region.Compared with ECS system,the systemenergy consumption,and the emission of different pollutants of ECSA system can be reduced by a maximum of 1.37 times.In cold region,the initial investment in an air source heat pump is higher due to the lower ambient temperature,resulting in an increase in the LOCH value of ECSA system.After the LOCH value of ECSA system in each region was optimized,the heating cost of the system was reduced,but also resulted in an increase in energy consumption and the emission of different pollutant gases.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part I:A Conductive and Convective Theoretical Heat Transfer Analysis for Molten Salt Cylindrical Shells at 565℃ and 700℃

In this paper a full theoretical thermal analysis of a large molten salt container,80-foot in diameter and 46-foot high,including a four-foot elliptic shell roof,is presented for two temperatures,the standard 565℃ and a futuristic 700℃,which substantially improves the efficiency of the molten salt containers through the use of a highly stable chloride salt called SS700(SaltStream 700).The theoretical analysis includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed theoretically using conductive heat transfer,however the area surrounding the soil surface around the bottom of the molten salt storage tank had convective heat transfer analysis included.The final designs presented in this paper seek to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃,which determines the thicknesses of the fiberglass and firebrick insulation.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part II:A Conductive and Convective Numerical Finite Element Heat Transfer Analysis for Molten Salt Cylindrical Shells at 700℃,and Comparison with Theoretical Analysis

In this paper a finite element thermal analysis model-using COMSOL-of a large molten salt container,80-foot in diameter and 46-foot high that includes a four-foot elliptic shell roof,is presented for a futuristic 700℃ design,which uses a highly stable chloride salt called SS700(SaltStream 700)that improves the efficiency of the tank when compared to the traditional 565℃.The FEA(finite element analysis)includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed by finite element using conductive heat transfer,however the area surrounding the soil surface around the bottom of the MS storage tank had convective heat transfer analysis included.The finite elements analyses presented are to verify the final fiberglass and firebrick insulation designs,which seeks to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃.These results are also compared to previously calculated theoretical results.

Intelligent Agent-Based Architecture for Demand Side Management Considering Space Heating and Electric Vehicle Load

Contraction of resilience on generation side due to the introduction of inflexible renewable energy sources is demanding more elasticity on consumption side. It requires more intelligent systems to be implemented to maintain power balance in the grid and to fulfill the consumer needs. This paper is concerned about the energy balance management of the system using intelligent agent-based architecture. The idea is to limit the peak power of each individual household for different defined time regions of the day according to power production during those time regions. Monte Carlo Simulation (MCS) has been employed to study the behavior of a particular number of households for maintaining the power balance based on proposed technique to limit the peak power for each household and even individual load level. Flexibility of two major loads i.e. heating load (heat storage tank) and electric vehicle load (battery) allows us to shift the peaks on demand side proportionally with the generation in real time. Different parameters related to heating and Electric Vehicle (EV) load e.g. State of Charge (SOC), storage capacities, charging power, daily usage, peak demand hours have been studied and a technique is proposed to mitigate the imbalance of power intelligently.

Research on Performance Optimization of Phase Change Thermal Storage Electric Heating Device

At present, the main heating method for reducing crude oil viscosity is electric heating, and the all-day electric heating method has the problems of high energy consumption and high cost. In order to meet the needs of environmental protection and industrial production, a new type of phase change thermal storage electric heating device was designed by combining the crude oil viscosity reduction heating method with valley price and phase change materials. The results indicate that as the inlet flow rate of the working fluid increases, the outlet temperature continuously decreases. And when the outlet temperature rises to 10?C, the inlet flow rate of the device can meet the flow range of 1.413 - 2.120 m3/h. At the same time, the addition of foam nickel makes the internal temperature of PCM more uniform, and the internal temperature of PCM decreases with the decrease of porosity of foam metal. By increasing the number of electric heating rods and reducing the power of individual electric heating rods, the structure of the device was optimized to significantly improve local high-temperature phenomena. The use of this device can maintain high heat exchange efficiency and reduce production costs.

Influence of the Fin Design on the Melting and Solidification Process of NANO3 in a Thermal Energy Storage System

The melting and solidification process of sodium nitrate, which is used as energy storage material, is studied in a vertical arranged energy storage device with two different bimetal finned tube designs （with and without additional lateral fins） for enhancing the heat transfer. The finned tube design consists of a plain steel tube while the material for the longitudinal （axial） fins is aluminum. The investigation analyses the influence of the lateral fins on the charging and discharging process. Three-dimensional transient numerical simulations are performed using the ANSYS Fluent 14.5 software. The results show that, every obstruction given by lateral fins reduces the melting and solidification velocity in direction to the outer shell.

Heat and power load dispatching considering energy storage of district heating system and electric boilers

As one of promising clean and low-emission energy, wind power is being rapidly developed in China.However, it faces serious problem of wind curtailment,particularly in northeast China, where combined heat and power(CHP) units cover a large proportion of the district heat supply. Due to the inherent strong coupling between the power and the heat load, the operational flexibility of CHP units is severely restricted in winter to meet the heat supply demand, which imparts considerable stress on the wind power connection to the grid. To promote the integration of wind power and enhance the flexibility of CHP units, this paper presented a method of heat and power load dispatching by exploring the energy storage ability of electric heating boilers and district heating systems. The optimization results indicate that the proposed method can integrate additional wind power into the grid and reduce the coal consumption of CHP units over the optimized period. Furthermore, the thermal inertia of a district heating system is found to contribute more to the reduction of coal consumption, whereas the electric heating boilers contribute to lower wind curtailment.

Heating Characteristics and Economic Analysis of a Controllable On-Demand Heating System Based on Off-Peak Electricity Energy Storage

The working principle of a controllable on-demand heating system based on off-peak electricity energy storage(COHSBOEES) is as follows: the cheap off-peak electricity energy is converted into heat energy for storage in the evening, and the heat energy can be extracted on demand for heating during daytime peak or flat electricity periods. This technology can promote the smooth operation of the power grid, solve the problem of peak regulation for the electrical network, and promote renewable energy consumption. Based on the controllable on-demand heating strategy, a COHSBOEES for a heating area of 1000 m^2 was designed and built. Variations in the energy consumption and operating cost of the COHSBOEES in different heating situations were analyzed. The results showed that, off-peak electricity energy storage for heating was energy saving in comparison with central heating when the heating intensity of the COHSBOEES was 70 W/m^2 and the on-demand heating rate was less than 73.0%, and the off-peak electricity energy storage for heating was energy saving at any on-demand heating rate when the COHSBOEES had a heating intensity of 50 W/m^2. After the COHSBOEES has been running for three complete heating seasons, when the off-peak electricity price was 0.25 yuan/kW·h, the energy consumption cost of the COHSBOEES can be saved by 77.6% in comparison with central heating.

Designing the cooling system of a hybrid electric vehicle with multi-heat source

In order to reduce the power consumption and meet the cooling demand of every heat source component, three kinds of multi-heat source cooling system schemes were designed base on the characteristic of power split hybrid electric vehicle （HEV）. Using the numerical simulation meth- od, the power system heat transfer model was built. By comparing the performance of three differ- ent schemes through the Simulink simulation, the best cooling system scheme was found. Base on characteristics of these cooling system structures, the reasonableness of the simulation results were analyzed and verified. The results showed that the cooling system designation based on the numerical simulation could describe the cooling system performance accurately. This method could simplify the design process, improve design efficiency and provide a new way for designing a multi-heat source vehicle cooling system.

LESSONS LEARNED: GREEN BUILDING DESIGN TECHNIQUES FOR OFF-GRID LOCATIONS

Over 25 percent of the world’s population lives without access to electricity from a utility-supplied grid[1].In under­developed and developing countries,the reason is primarily a lack of government-sponsored utility infrastructure due to the high cost of power line extension.In developed countries,power line extension costs are again the primary fac­tor in lack of a grid connection,as in most cases the end user must foot the bill for such improvements.In the United States,power line extension can cost over$50,000 per kilometer[2],so the cost of an off-grid electrical system that uses renewable sources to charge a large battery bank for energy storage can compare favorably to that of grid exten­sion-but not always.However,both the design and implementation of such off-grid renewable energy systems differ greatly from more common grid-tied applications,where the utility grid is used as“battery”with which the system can buy and sell electrical energy from and to the utility as needed.Energy efficiency and conservation are paramount in all off-grid renewable energy system designs,as these measures extend at low cost the hours or days of autonomous operation time before a backup power source(usually an internal-combustion generator)must be used for battery charging during periods of no input from renewable solar,wind,or hydroelectric sources.The techniques used in designing and operating an off-grid building can seem extreme compared to the norm,and provide a whole set of new challenges if the retrofitting of an existing structure is required.But the lessons learned from these experiences are quite relevant to modern buildings in urban and suburban areas,as the goal is the same-first reduce energy consumption through efficiency and conservation,rather than simply increasing energy production.With off-grid systems,the payback from these measures simply has a more immediate effect.And at the end of the day,non-electrical energy efficiency measures prove to be at least as effective as electrical ones.

Coordinated control strategy for wind power accommodation based on electric heat storage and pumped storage

To solve the severe problem of wind power curtailment in the winter heating period caused by ＂power determined by heat＂ operation constraint of cogeneration units, this paper analyzes thermoelectric load, wind power output distribution and fluctuation characteristics at different time scales, and finally proposes a two level coordinated control strategy based on electric heat storage and pumped storage. The optimization target of the first level coordinated control is the lowest operation cost and the largest wind power utilization rate. Based on prediction of thermoelectric load and wind power, the operation economy of the system and wind power accommodation level are improved with the cooperation of electric heat storage and pumped storage in regulation capacity. The second level coordinated control stabilizes wind power real time fluctuations by cooperating electric heat storage and pumped storage in control speed. The example results of actual wind farms in Jiuquan, Gansu verifies the feasibility and effectiveness of the proposed coordinated control strategy.

Electricity Storage With High Roundtrip Efficiency in a Reversible Solid Oxide Cell Stack

We theoretically investigate the electricity storage/generation in a reversible solid oxide cell stack. The system heat is for the first time tentatively stored in a phase-change metal when the stack is operated to generate electricity in a fuel cell mode and then reused to store electricity in an electrolysis mode. The state of charge （H2 frication in cathode） effectively enhances the open circuit voltages （OCVs） while the system gas pressure in electrodes also increases the OCVs. On the other hand, a higher system pressure facilitates the species diffusion in electrodes that therefore accordingly improve electrode polarizations. With the aid of recycled system heat, the roundtrip efficiency reaches as high as 92% for the repeated electricity storage and generation.

Thermo-physical properties of rubber seed useful in the design of storage structure

This study was carried out to determine the thermo-physical properties of rubber seed in the moisture range of 9.1%to 14.8%(w.b.).The length,width,thickness,measured surface area,bulk density and true density increased with increasing moisture content with high coefficients of determination(significant at p<0.05).Their optimum values at 14.8%moisture content were 17.00 mm,11.94 mm,8.26 mm,285.20 mm^(2),295.00 kg/m^(3) and 470.67 kg/m^(3),respectively.The angle of repose increased as moisture content increased with low coefficient of determination and has optimum value of 28.81°at 14.8%moisture content.The specific heat capacity and thermal conductivity decreased linearly while thermal diffusivity increased exponentially with an increase in moisture content(significant at p<0.05).The optimum values of specific heat capacity,thermal conductivity and diffusivity at 14.8%moisture content were 55.84 kJ/(kg.K),0.032 W/(m.K)and 1.93×10^(-9) m^(2)/s,respectively.The results are essential in the design of storage structure for rubber seed.

Optimization of DC Resistance Divider Up to 1200 kV Using Thermal and Electric Field Analysis

Self-heating and electric field distribution are the primary factors affecting the accuracy of the Ultra High Voltage Direct Current(UHVDC)resistive divider.Reducing the internal temperature rise of the voltage divider caused by self-heating,reducing the maximum electric field strength of the voltage divider,and uniform electric field distribution can effectively improve the UHVDC resistive divider’s accuracy.In this paper,thermal analysis and electric field distribution optimization design of 1200 kV UHVDC resistive divider are carried out:(1)Using the proposed iterative algorithm,the heat dissipation and temperature distribution of the high voltage DC resistive divider are studied,and the influence of the ambient temperature and the power of the divider on the temperature of the insulating medium of the divider is analyzed;(2)Established the finite element models of 1200 kV and 2×600 kV DC resistive dividers,analyzed the influence of the size of the grading ring and the installation position on the maximum electric field strength of the voltage divider,and calculated the impact of the shielding resistor layer on the vicinity of the measuring resistor layer.The research indicates that:(1)The temperature of the insulating medium is linearly related to the horsepower of the voltage divider and the ambient temperature;(2)After the optimized design of the electric field,the maximum electric field strength of the 1200 kV DC resistive divider is reduced to 1471 V/mm,which is about 24% lower than that of the unoptimized design;(3)Installing the shielding resistor layer can significantly improve the electric field near the measuring resistor layer.This paper has an important reference function for improving the accuracy of the UHVDC resistive divider.

储液式CCS耦合P2G的综合能源系统低碳经济调度

为应对电转气P2G(power-to-gas)和碳捕集系统CCS(carbon capture system)在可再生能源出力不足时耦合失效的问题,考虑对常规CCS引入CO_(2)储液罐以加强P2G和CCS的耦合。首先,构建储液式CCS和P2G的耦合模型,利用储液罐将CCS捕集的CO_(2)时移至可再生能源富足时段,供P2G再利用;其次,构建储液式CCS与P2G耦合的电热气综合能源系统日前优化调度模型;最后,以北方某工业园区为例进行仿真。结果证明所提模型可以充分利用CCS捕集的CO_(2),从而获得更好的经济和环境效益。

氢储能系统容量双层鲁棒随机优化配置方法

氢能作为一种清洁无污染、能量密度大的二次能源,是大规模消纳新能源的理想储能载体,耦合氢储能系统和可再生能源的电热氢综合能源系统为消纳新能源提供新的思路和方案。围绕电热氢综合能源系统中如何以经济合理的方式投入氢储能设备展开研究,解决氢储能设备容量的合理配置问题以及考虑源荷不确定性对电热氢综合能源系统运行的影响,提出了一种考虑季节性存储和源荷不确定性的电热氢综合能源系统中氢储能容量优化配置方法。首先针对风电功率预测误差较大,电热气负荷预测精度较高的特点,分别采用不确定集和抽样场景描述源和荷两侧的不确定性。然后建立了考虑源荷不确定性和季节性存储的氢储能容量配置双层鲁棒随机优化模型,其上层问题以年化投资成本和运行成本的总成本最小化为目标确定氢储能系统装置容量,下层问题采用两阶段鲁棒随机优化模型模拟电热氢综合能源系统典型日在风电出力最恶劣场景下的最优运行方案。由于该模型难以直接求解,提出基于粒子群优化算法和列与约束生成算法对该类复杂模型进行求解。最后,通过对某个电热氢综合能源系统算例进行分析,算例分析结果验证了所提方法的有效性,获得的氢储能系统容量优化配置方案能够促进风电消纳和提高系统运行的经济性。

考虑阶梯式碳交易与电热需求响应的综合能源系统经济调度

在能源安全新战略背景下,推动可再生能源发展、降低碳排放将是未来发展趋势。为了消纳大规模风电的弃风功率以提升电网的调峰能力,首先考虑阶梯式碳交易机制,采用碳交易市场,利用碳交易价格达到控制碳排放的目的;其次基于分时电价形成用户用电舒适度与用热舒适度,构建电热负荷需求响应模型,在掌握电锅炉、储热装置和热需求可时移特性的基础上,通过风电供给价格弹性系数描述风电出力与电锅炉协议电价之间的变化;最后通过综合满意度指标评估负荷响应能力,构建了考虑需求响应和阶梯式碳交易机制的含蓄热式电锅炉综合能源系统优化调度模型,实现系统经济运行,并采用CPLEX求解器对所构建模型进行求解。结果表明所提方法能够有效促进风电消纳,减少碳排放量且有效降低系统运行成本。

电阻式熔盐加热器内部传热特性研究

高温熔盐电加热器是储热系统中实现电热转换的核心设备,掌握内部温度分布特性是推动其结构优化的关键。文章建立了传统电阻式熔盐加热器计算模型,采用CFD软件,通过求解三维N-S方程和能量方程,研究了加热器内部温度分布特点,得到了电加热器内部温度分布在不同工况下的变化规律。结果表明:沿流动方向上熔盐和管壁温差逐渐增加,而多组串联布置能够有效降低传热温差,在加热器连接处二者温差可从27℃降低至2℃;同时,由于内部加热管密集程度不一致,横截面内中心位置熔盐、电阻丝、填充材料温度明显高于边缘位置,且伴随着负荷的增加温度梯度也逐渐增加,当平均热流密度从5.71 W/cm^(2)增加至28.57 W/cm^(2)时,截面熔盐温差从49℃升高至68℃,可以看出,合理分配电加热管排布是降低截面温差、减小热应力的关键。

考虑氢储能和需求响应的综合能源系统双层优化配置

在双碳目标下,为改善综合能源系统功率不平衡,提高能源运营商收益,降低用户购能成本,首先,结合氢储能可作为源-荷-储的优点以及电制热的能源转换特性,设计了考虑氢储能的综合能源系统双层框架。其次,根据两种不同时间尺度,提出了一种考虑负荷侧需求响应和含电制热设备用户群的综合能源系统氢储能双层优化配置模型,上层模型结合氢储能特性进行长时间尺度优化配置;下层模型利用需求响应和电制热设备对用户群负荷进行优化,以求解短时间尺度含氢储能综合能源系统优化运行问题。再次,采用KKT条件和Big-M法将模型转为单层线性问题。最后,结果显示,通过配置氢储能以及采用电制热设备和需求响应,可提高运营商收入和新能源消纳,降低用户群成本,减少功率失衡风险。

考虑变掺氧富氧燃烧与利用LNG冷能的LAES的综合能源系统低碳经济调度

为促进风电消纳,减少火电机组的碳排放,解决综合能源系统(Integrated Energy System,IES)低碳经济运行问题,文中引入变掺氧富氧燃烧技术对燃气机组进行改造,并结合利用液化天然气(Liquefied Natural Gas,LNG)冷能的液化空气储能(Liquid Air Energy Storage,LAES),提出了一种电热气冷IES低碳经济优化策略。首先,构建含变掺氧富氧燃烧燃气机组、利用LNG冷能的LAES、电转气(Power To Gas,P2G)设备、中央空调和溴化锂制冷机的IES架构,并建立各设备的数学模型;其次,引入阶梯式碳交易机制,建立了以系统运行成本最小为目标的电热气冷IES低碳经济调度模型;最后,采用MATLAB调用GUROBI求解器对多个场景进行求解,验证了文中提出的低碳经济优化调度策略可以提高系统的风电消纳、有效降低系统运行成本,实现碳减排。