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Analysis On The Heat Storage/Release Effects Of Solar Energy Water-cycling System In Sliding- Cover Energy-saving Solar Greenhouses

Posted on:2019-03-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:X J TongFull Text:PDF
GTID:1363330593451907Subject:Facilities for horticulture
Abstract/Summary:PDF Full Text Request
Solar greenhouse is the main horticulture facility in north of China,with solar energy as the main energy source,wall and soil as the main heat storage body.It is characterized by high efficiency,energy-saving and low cost.It has solved the problem of vegetable production during winter and spring in the north of China,and has become one of the pillar industries to solve the problem of“Agriculture,Rural areas and Farmers”in China,which has produced huge economic,social and ecological benefits.But there are many disadvantages in the traditional solar greenhouses:limited heat storage capacity of the wall and soil,badly shaded by the east and west gables,the uneven distribution of the light and air temperature between the north-south direction,as well as the poor ability of the heat preservation materials to prevent wind,rain,snow and fire,and the utilization of the land is not well either.In view of the existence issues of the traditional solar greenhouses,a new kind of half circular arc Sliding-cover Energy-saving Solar Greenhouse assembled with heat preservation color steel plate has been developed.The automatic control of thermal insulation cover of solar greenhouse is realized,which lays a foundation for the modernization development of solar greenhouses.At the same time,an active Solar energy Water-cycling System has been developed with water as the heat storage medium to solve the problem of heat storage/release of Sliding-cover Energy-saving Solar Greenhouse,which has lay the foundation for the improvement of the wall structure and transformation of fabricated construction for solar greenhouses and provided theoretical and technical guidance for automate environmental control in solar greenhouses.Therefore,at the same time,a preliminary study on the active heat storage/release effect of Solar energy Water-cycling System relying on the Sliding-coving Energy-saving Solar Greenhouse with solar energy as heat source and water as heat storage medium has been carried out,on the basis of the research group.At first,the temporal and spatial variation of solar radiation,light intensity,spectral radiance and air temperature and relative humidity indoor has been analyzed to clarify the light and temperature characteristics of Sliding-coving Energy-saving Solar Greenhouse.Secondly,the application effects experimentally and heat storage performance of Solar energy Water-cycling System have been analyzed.Finally,analysis on the heat/release process for heat collector/releaser and storage tank of Solar energy Water-cycling System in detail has been carried out,and a heat storage and release model based on diurnal variation of water temperature in the storage tank of three stages in a diurnal cycle has been set up to simulate water temperature in every stage.Then the heat collector/releaser area and storage tank volume under different set-point air temperature indoor has been calculated based on this model and energy balance in Sliding-coving Energy-saving Solar Greenhouse at nighttime.This system has solved the problems of heat storage and release for Sliding-cover Energy-saving Solar Greenhouse.The main research results are as follows:1.The variation rules of solar radiation,light intensity and spectral radiance on temporal and spatial in the Sliding-cover Energy-saving Solar Greenhouse on the typical sunny days of different seasons,and the air temperature and relative humidity day and night in winter had been analyzed,with the Liaoshen Type energy-saving Solar Greenhouse as control.Later,the simulation of solar radiation indoor and outdoor was carried out to set the basis for study of Solar energy Water-cycling System.The results showed that the angle and shape of roof surface had significant influence on the distribution of sunlight and solar energy capture.The the solar radiation transmittance and daily solar energy intercepted of in Sliding-cover Energy-saving Solar Greenhouse in winter were 15.4%and 11.6%higher than control,and the total solar radiation in indoor within 300400 W·m-2 for more than 30 minutes,and the light distribution was uniform in the north-south direction.Solar radiation near the north slope of sliding greenhouse exists in the form of diffuse radiation in summer,and the average solar radiation was significantly lower than control,the solar radiation transmittance decreased by 20.9%on average,and the solar intercepted decreased by 21.9%.And the difference between the two greenhouses in spring and autumn was not significant.Before Solar energy Water-cycling System at night,air temperature dropped slower,and 0.61.5?higher than control.It reflected better heat preservation performance of thermal insulation covers.And the air temperature indoor was higher 23?in Sliding-cover Energy-saving Solar Greenhouse than control at night in sunny winter,and the air temperature distribution was relatively uniform in north-south west-east and vertical direction,the relative humidity was significantly lower than control at night.In general,the structure of Sliding-cover Energy-saving Solar Greenhouse is superior to the traditional solar greenhouse in terms of meeting the requirements of crops for lighting and solar energy intercepted.2.The affecting factors on heat storage/release performance of Solar energy water-circling System in solar greenhouse had been studied.The results showed that different heat collecting materials and the frame of heat collector/releaser open or closed had significant influence on the heat storage,and the thickness of the closed space had no significant effect on the daily heat storage and release.The daily heat storage capacity of the system with PE pipe and brown PC board as heat collector was significantly more than that of transparent PC board,which was increased by 80.4%and 70.6%,respectively.Flat plate solar collectors had higher heat collecting efficiency and more heat storage than others,but they cannot be used as heat releaser.Compared with the open type,water temperature in storage tank of the closed one was increased by 2.7°C on average,and the daily heat storage was increased by 22.03%.The difference between different thickness the closed cavity of was not significant.And the final water temperature and heat storage in storage tank were both linearly related to water storage capacity,initial water temperature,solar radiation and air temperature indoor.3.The effects on heat storage of Solar energy Water-cycling System in Sliding-cover Energy-saving Solar Greenhouse in different regions were analyzed and compared.The results showed that Solar energy Water-cycling System had remarkable effects on heat storage and temperature increase during the winter.And the effects on heat storage of the system with dual-line was obviously improved in Lingyuan where the region with better lighting conditions.The water temperature in storage tank of the two kinds of heat collecting units increased by 34°C respectively on winter sunny days during the testing period in Shenyang.The total daily heat storage of the two heat collecting units was 533.96 MJ,and average was 443.75 MJ,and the air temperature was increased by 2.53°C at night than control.The average heat collecting efficiency was 28%,the heat releasing efficiency was 44%.In cloudy days,the water temperature increased by about 2°C,the daily heat storage was 203.48 MJ,the air temperature was about 2°C higher than control.The average heat collecting efficiency was 19%,and the heat releasing efficiency was about 92%.The system heated the greenhouse during the operational period at nighttime,so that the air temperature in the north side was higher,and the temperature difference between north and south was about 0.5°C.And water temperature in storage tank increased by 6.7?during the system running period in Lingyuan,and the daily heat storage was 902.57 MJ at most,the average was 693.76 MJ.The average heat collecting efficiency was 42%,the accumulated heat storage per unit area of heat collector releaser was2.51 MJ·m-2.The average heat release was 465.6 MJ during the nighttime,the average heat releasing efficiency was 65%,the heat release per unit area was 1.29 MJ·m-2,and the heat release rate was 59.7 W·m-2.4.The heat storage/release process of two kinds of heat collecting units with PE pipe and PC board as heat collecting materials was analyzed based on heat transfer theory respectively.The heat transfer process of heat collector/releaser and storage tank was analyzed according to heat transfer theory.There were three parts of heat exchange,like the absorption of solar radiation by heat collector/releaser,heat exchange between air indoor and surface of heat collector/releaser and thermal energy variation in storage tank.The theoretical analysis and calculation of each part of the heat transfer process of the Solar energy Water-cycling System were carried out,and the energy balance calculation formulas of the two kinds of different heat collecting units?PE pipe and PC board?of three stages in a diurnal cycle were obtained.The heat storage and release model based on the water temperature in storage tank was established,and the area of heat collector/releaser and the volume of storage tank were determined with PC board according to the model and energy balance in Sliding-cover Energy-saving Solar Greenhouse at nighttime.The results showed that the required heat collector/releaser area and storage tank volume increased gradually with the set-point air temperature indoor,heat collector/releaser area and storage tank volume of the system showed a trend of gradual increasing with the growth of air temperature.And required for heat collector/releaser area of per storage tank volume?A/V?was still gradually increased,that is,the increase rate of required heat collector/releaser area was higher than storage tank volume,indicated that the effect on the improvement of heat storage/release performance with increasing heat collector/releaser area was more significant than that of storage tank volume.When the air temperature was above-27?outdoor at night,to maintain air temperature not less than 12?,Sliding-cover Energy-saving Solar Greenhouse with 660 m2 need 12 pieces of 0.006 m transparent PC board?2 m×5 m?,that is 113.5 m2 heat collector/releaser matched with 14.4 m3 storage tank.
Keywords/Search Tags:Sliding-cover Energy-saving Solar Greenhouse, light and temperature characteristic, solar energy, water-cycling system, heat/release storage effects
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