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.

The Effect of Water Flow Velocity on Heat Collection Performance of Active Heat Storage and Release System for Solar Greenhouses

In order to explore the influence of water velocity on the heat collection performance of the active heat storage and release system for solar greenhouses,six different flow rates were selected for treatment in this experiment.The comprehensive heat transfer coefficient of the active heat storage and release system at the heat collection stage was calculated by measuring the indoor solar radiation intensity,indoor air temperature and measured water tank temperature.The prediction model of water temperature in the heat collection stage was established,and the initial value of water temperature and the comprehensive heat transfer coefficient were input through MATLAB software.The simulated value of water temperature was compared with the measured value and the results showed that the best heat transfer effect could be achieved when the water flow speed was 1.0 m3h-1.The average relative error between the simulated water tank temperature and the measured value is 2.70-6.91%.The results indicate that the model is established correctly,and the variation trend of water temperature can be predicted according to the model in the heat collection stage.

Feasibility Analysis on the Integrated Application of Solar Energy, Biogas, Coal-fired Boiler and Radiant Floor Heating for Rural Residence

The feasibility of adopting a balanced energy mix mode (domestic solar energy, biogas, coal-fired boiler and radiant floor heating) was proposed. Taking a typical rural residence in Zhengzhou City for example, the study through theoretical analysis and calculation showed that such a balanced energy mix is an economic way and efficient in saving energy and reducing air pollution, and elaborated the theoretical feasibility of popularizing such a heat supply mode in rural areas.

Solar Desalination with Latent Heat Storage Materials and Solar Collector

Availability of clean water is going to become one of biggest demands of the country. Even though there arc various technologies available for purification of water harnessing solar energy fits the purpose for future problems. Distillation is one of many processes available for water purification, and solar energy is one of several forms of heat energy that can be used to energize this process. In this review a study is made to enhance the productivity of the solar stills by connecting solar still with latent heat storage and solar air heater in series and other factors like improving evaporation rate by maintaining Low depth, more exposure area, heat addition by solar collector and presence of latent heat storage material, which is a paraffin wax as a integral part of still. Latent heat storage is one of the most efficient ways of storing thermal energy. Unlike the sensible heat storage method, the latent heat storage method provides much higher storage density, with a smaller temperature difference between storing and releasing heat. Further augmentation of the yield by scraps, pebble, and sand are added.

Numerical Study of Thermal Performance of Phase Change Material Energy Storage Floor in Solar Water Heating System

The conventional solar heating floor system contains a big water tank to store energy in the day time for heating at night,which takes much building space and is very heavy.In order to reduce the water tank volume even to cancel the tank,a novel structure of integrated water pipe floor heating system using shape-stabilized phase change materials(SSPCM)for thermal energy storage was developed.A numerical model was developed to analyze the performance of SSPCM floor heating system under the intermittent heating condition,which was verified by our experimental data.The thermal performance of the heating system and the effects of various factors on it were analyzed numerically.The factors including phase transition temperature,heat of fusion,thermal conductivity of SSPCM and thermal conductivity of the decoration material were analyzed.The results show that tm and kd are the most import influencing factors on the thermal performance of SSPCM floor heating system,since they determine the heat source temperature and thermal resistance between SSPCM plates and indoor air,respectively.Hm should be large to store enough thermal energy in the day time for nighttimes heating.The effects of kp can be ignored in this system.The SSPCM floor heating system has potential of making use of the daytime solar energy for heating at night efficiently in various climates when its structure is properly designed.

Experimentation of a Plane Solar Integrated Collector Storage Water Heater

In order to popularize the use of the solar-water heaters, especially in the residential and tertiary sectors with the third world, it appears to be necessary to reduce their cost while improving their performances. It is the object of this integrated storage collector thus created and tested in the south of Tunisia. It is simply made up of a tank playing the double part of solar absorber and storage tank of warm water, of a glazing to profit from the greenhouse effect and of an insulating case. Its measured energy performances, by the method of input-output proves its effectiveness to produce hot water, in spite of its simplicity of manufacture, usage and maintenance. Indeed a temperature of water exceeding 70?C is reached towards the afternoon True Solar Time, and for an efficiency of 7%. Thus, this type of collector with integrated storage is entirely satisfactory and could be available to larger mass.

Effect of Periodic Variation of Sol-air Temperature on the Performance of Integrated Solar Collector Storage System

Parametric study is carried out in the present article to investigate the unsteady performance of solar energy gain and heat retention of two different integrated-collector-storage systems. The systems are the conventional rectangular-shaped storage tank and the modified tank shaped as rectangular cuboid with one semi -circular top. The two systems have the same absorber surface area and volume for water. The heat and fluid flow is assumed to be unsteady, two-dimensional, laminar and incompressible. The performances of the two systems are evaluated based on the maximum temperature in the system during daytime heating period and nighttime cooling period. For comprehensive study, 24 hours simulations for 3 cases with different wall boundary condition impose on the absorber plate are investigated. The simulation results show that the modified system has better heat retain than the conventional system. Periodic variations of both systems are investigated, and it is found that both systems show consistent results on different days. The modified system is able to store most of the thermal energy in the semi-circular top region with higher temperature than that of the conventional system.

Technical and Economic Aspects of Solar Space Heating in Palestine

A computer analysis of solar heating has been performed for Palestine. Results are presented for a prototype building using either fuel oil or gas under different heating loads in three climatic regions （Jordan valley, coastal, and hilly）. Cumulative cost flows are compared for the life-cycle present value technique. Optimum design magnitudes are determined for maximum life-cycle savings. The payback period for capital invested in a solar system, and total savings are found for the optimum conditions. Variations of system performance are estimated. The effects of collector slope, proportionate storage tank volume, heat-exchanger parameters, and the design load on system performance are studied. Finally the economics of solar heating in Palestine are discussed and recommendations are made for increased utilization of solar energy.

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.

Energy and Buildings

In this paper,the thermal performance of a rectangular latent heat storage unit(LHSU)coupled with a flat-plate solar collector was investigated numerically.The storage unit consists of a number of vertically oriented slabs of phase change material(PCM)exchanging heat with water acting as heat transfer fluid(HTF).During the day(charging mode),the water heated by the solar collector goes into the LHSU and transfers heat to the solid PCM which melts and hence stores latent thermal energy.The stored thermal energy is later transferred to the cold water during the night(discharging process)to produce useful hot water.The heat transfer process was modeled by developing a numerical model based on the finite volume approach and the conservation equations of mass,momentum,and energy.The developed numerical model was validated by comparing the simulation results,obtained by a self-developed code,with the experimental,numerical and theoretical results published in the literature.The numerical calculations were conducted for three commercial phase change materials having different melting points to find the optimum design of the LHSU for the meteorological conditions of a representative day of the month of July in Marrakesh city,Morocco.The design optimization study aims to determine the number of PCM slabs,water mass flow rate circulating in the solar collector and total mass of PCM that maximize the latent storage efficiency.The thermal performance of the LHSU and the flow characteristics were investigated during both charging and discharging processes.The results show that the amount of latent heat stored in the optimum design of the storage unit during the charging process is about 19.3 MJ,16.54 MJ,and 12.79 MJ for RT42,RT50,and RT60,respectively.The results also indicate that depending on the mass flow rate of HTF,the water outlet temperature during the discharging process varies within the temperature ranges 43.6℃-24℃,51.7℃-24℃,and 62.86℃-24℃for RT42,RT50,and RT60,respectively.

Solar Thermal Systems Performances versus Flat Plate Solar Collectors Connected in Series

This paper shows the modeling of a solar collective heating system in order to predict the system performances. Two systems are proposed: 1) the first, Solar Direct Hot Water, which is composed of flat plate collectors and thermal storage tank, 2) the second, a Solar Indirect Hot Water in which we added an external heat exchanger of constant effectiveness to the first system. The mass flow rate by a collector is fixed to 0.04 Kg·s–1 and the total number of collectors is adjusted to 60. For the first system, the maximum average water temperature within the tank in a typical day in summer and annual performances are calculated by varying the number of collectors connected in series. For the second, this paper shows the detailed analysis of water temperature within the storage and annual performances by varying the mass flow rate on the cold side of the heat exchanger and the number of collectors in series on the hot side. It is shown that the stratification within the storage is strongly influenced by mass flow rate and the connections between collectors. It is also demonstrated that the number of collectors that can be connected in series is limited. The optimization of the mass flow rate on cold side of the heat exchanger is seen to be an important factor for the energy saving.

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.

Steel-Tinplate as a Solar Wall Panel and Its Effectiveness

The aim of the research was to investigate black colored steel-tinplate use for absorber and covering material of the collector and compare the efficiency of three types of air heating collectors. This heated air can be exploited for drying of agricultural products, room ventilation and room heating etc. 0.1 × 0.5 × 1.0 meter long FPC （fiat-plate collector） with a sun following platform was built. Air velocity at the experiments was v = 0.9 m/s. Collectors of insulated and un-insulated surfaces with steel-tinplate absorber as a covering material warmed the ambient air up to 10-12 and 5-6 degrees correspondingly （at irradiance 800 W/m^2）. This difference indicates the great importance of insulating the collector body. It can be explained with intense heat exchange between the absorber and ambient air which reduces the efficiency of the collector. There was good correlation with irradiance and the air heating degree. The investigations showed that more effective FPC had the collector with absorber tinplate in the middle of the collector body. At favorable weather conditions the heating degree of the ambient air at the outlet reaches 6-8 degrees more that at the outlet of the insulated collector covered by steel-tinplate.

New Hybrid CHP System Integrating Solar Energy and Exhaust Heat Thermochemical Synergistic Conversion with Dual-Source Energy Storage

For the efficient use of solar and fuels and to improve the supply-demand matching performance in combined heat and power(CHP)systems,this paper proposes a hybrid solar/methanol energy system integrating solar/exhaust thermochemical and thermal energy storage.The proposed system includes parabolic trough solar collectors(PTSC),a thermochemical reactor,an internal combustion engine(ICE),and hybrid storage of thermal and chemical energy,which uses solar energy and methanol fuel as input and outputs power and heat.With methanol thermochemical decomposition reaction,mid-and-low temperature solar heat and exhaust heat are upgraded to chemical energy for efficient power generation.The thermal energy storage(TES)stores surplus thermal energy,acting as a backup source to produce heat without emitting CO_(2).Due to the energy storage,time-varying solar energy can be used steadily and efficiently;considerable supply-demand mismatches can be avoided,and the operational flexibility is improved.Under the design condition,the overall energy efficiency,exergy efficiency,and net solar-to-electric efficiency achieve 72.09%,37.65%,and 24.63%,respectively.The fuel saving rate(FSR)and the CO_(2) emission reduction(ER_(CO_(2)))achieve 32.97%and 25.33%,respectively.The research findings provide a promising approach for the efficient and flexible use of solar energy and fuels for combined heat and power.

A numerical and experimental study of a dual-function solar collector integrated with building in passive space heating mode

A newly designed solar collector named dual-function solar collector is proposed.The dual-function solar collector integrated with building can perform in two different modes:working as a passive space heating collector in cold sunny days such as in winter,or working as a facade water heating collector in hot days such as in summer.An experimental study has been carried out to investigate the performance of the novel system in space heating mode,whilst,the dynamic numerical model has been established and validated.The experimental and numerical results show that during the period of the measurement from 9:00 to 17:00,the mean indoor temperature was up to 24.7°C while the mean ambient temperature was only 4.8°C,and a temperature stratification was present in the room.Moreover,a numerical study on the effect of optical property of coatings has been carried out.

Dual-Roof Solar Greenhouse—A Novel Design for Improving the Heat Preserving Capacity in Northern China

Dual-roof solar greenhouse, a new style of solar greenhouse, was designed in this study intending to reduce heat loss in cold time and improve land use efficiency in Beijing, the Capital city of China. Designing and applying the dual-roof greenhouse in metropolitan area had dual effects of saving energy and enhancing land use efficiency. According to the monitoring study and analysis conducted in winter of 2012, the averaged night temperature of south room was about 12.1°C in December, which was satisfying for growing average leaf vegetables. Total energy saved by dual-roof in whole winter was quantified as 1.1 × 107 MJ&#46yr-1 (winter), potentially about 37.4 t coal was saved in Beijing area during whole winter-growing period. Considering the application of north room, the land use efficiency was improved by 62.5% in dual-roof solar greenhouse.

Performance analysis of a novel tobacco-curing system with a solar-assisted heat pump

A novel tobacco-curing system with a solar-assisted heat pump was proposed.The proposed system has various advantages,such as reducing energy consumption and pollutant emissions and enhancing the stability of system operation.The thermal characteristics of the system under different climate conditions were analyzed,and the economic and environmental benefits of different tobacco-curing technologies were compared.Results indicated that the dehydration rate,the mass flux of exhaust air,and the heat load of the novel tobacco-curing system in different months had similar changes with the baking time,and all reached the maximum in the later stage of color fixing.Compared with the power saving rate of a heat pump tobacco-curing system,that of the novel system reached 25.9%-35.1%.The dry leaf curing cost of the novel system was only 0.86-1.06 yuan/kg,which can reduce the cost by more than 60%compared with traditional coal-burning tobacco-curing systems in China.Compared with other parts of the tobacco leaf,the top leaf had the lowest dry leaf curing cost due to its highest mass of dry leaf.The payback period and the annual CO_(2) emission reduction of the novel system were 3.0-3.7 a and 15586 kg,respectively.

Thermal Performance Study of Three Models of Solar Air Heater Made of Concrete

An experimental study was conducted on three models of solar collectors having an absorber made of concrete designed and built in the TPL （Thermal Process Laboratory）. A sequence of tests was performed on these models for the two air circulation models （forced and natural） in order to compare their thermal performance. The results are presented in terms of useful energy, stored energy and thermal efficiency of each model.

计及AA-CAES与PTC集成的综合能源系统运行优化与性能分析

为进一步发挥综合能源系统的多能互补优势,提出一种计及先进绝热压缩空气储能(AA-CAES)与槽式太阳能集热器(PTC)集成的综合能源系统(IES-PTC-CAES)优化运行策略。首先,对AA-CAES、PTC以及系统中其他设备进行分析并建立相应模型;进而以经济性、环保性和能效性为优化目标,以设备运行的关键参数为优化变量,基于分时电价建立了协同优化策略,并通过K-means算法将模拟出的典型年负荷聚类为典型日负荷;最终,使用并行式的遗传算法对系统进行寻优,得到不同目标下IES-PTC-CAES的最优运行策略。结果表明:与参考系统相比,IES-PTC-CAES系统经济目标下总成本降低了14.61万元,环保目标下二氧化碳排放量减少了6194.38 kg。

多源分布式换能系统构建理论方法研究与应用

“双碳”背景下分布式换能系统以其在低碳环保方面的显著优势逐渐在集中供热领域得到应用。本文针对分布式换能系统中热泵、太阳能集热器、板式换热器和燃料电池等关键单元提出了单元能耗评价方法,并通过EES软件对各单元进行了热力学建模以定量评价不同单元在不同工况下的经济性,进而提出分布式换能系统的构建方法以获得流程经济性最优化。以此为依据搭建了最优化流程,并以北京地区某小区为例分析了该系统的供暖季性能,最后进行了经济性和碳减排分析。结果表明:室外温度在-10~5℃范围内变化时,该新型分布式换能系统的COP为2.69~4.43,太阳能集热器效率为45.19%~61.87%,燃料电池日发电量为8047.4~32228.0 kW·h;与常规热力站相比,该新型分布式换能系统的运行成本节省率为32.66%~53.92%,碳减排率为69.07%~73.29%。