| Based on the changes in heating methods under the current coal-to-electricity policy,as well as the demand for energy storage technology by shifting peaks and valleys from the power grid,the development of valley-electric heat storage heating technology can make full use of excess electricity and balance the requirements of clean heating.The grid load can produce economic benefits even under the conditions of peak and valley electricity prices.Due to the limitation of the thermal conductivity of the phase-change material itself,the current phase-change heat storage devices have problems such as low efficiency in converting electrical energy into effective heat output,which limits the popularization and application of valley-electric heat storage devices.Therefore,this paper proposes a simple and practical phase change heat storage device that can be combined with the wall to form a valley electricity heat storage wall module.The heat storage/release performance of the basic components of the device is studied through experiments and numerical simulations.And its influencing factors,as well as economic analysis of a calculation example of the actual scale of heat use.The main conclusions are as follows:1.A composite phase change material suitable for phase change thermal storage electric heating devices has been developed.Paraffin wax with a phase transition temperature of 62? was selected as the phase change material,and expanded graphite(EG),a porous material,as an additive to enhance its thermal conductivity.Different proportions of composite phase change materials(PCM)were prepared and their thermal properties were tested.The thermal conductivity of composite PCM increases with the increase of EG content.When the mass fraction of EG is 20%,the thermal conductivity of composite PCM increases to 27.3 times that of pure paraffin.The phase transition temperature of the composite PCM is almost unchanged,but the latent heat of phase transition will decrease with the increase of the EG ratio.After comprehensively considering the thermal conductivity and heat storage density,8wt%composite PCM was finally selected as the subsequent heat storage material.2.The basic parameters of the heat storage device were determined through the project estimate of the heating scene,and the heat storage unit heat storage and release characteristics experimental platform was built.The heat storage efficiency,instantaneous heat release efficiency and effective heat release efficiency were introduced to evaluate its thermal performance.The experiment found that: In the pure paraffin unit,the application of composite PCM can improve the heat storage efficiency and effective heat release efficiency.The heat storage efficiency is increased from 92.6%of pure paraffin to 97.3%,and the effective heat release efficiency is increased from 50%to 64%.3.The improvement of the effective heat release efficiency in the heat release process is the key to improving the overall thermal performance of the system.The heat release process is focused on,and the influence of the operating conditions on the heat release performance of the heat storage unit is discussed: under the same inlet temperature and heat storage capacity,the heat exchange fluid The smaller the flow rate,the lower the instantaneous heat release power of the phase change unit,but the longer the effective heat release time.Under the same inlet temperature,heat exchange fluid flow rate and the same heat storage conditions,the greater the aspect ratio of the heat storage unit's overall dimensions,The faster the heat release rate,the higher the effective heat release efficiency,and the highest effective heat release rate in the simulated working conditions is 82.3%.4.The application form of valley electricity heat storage device is proposed.The heat storage device is combined with the wall to form a valley electricity heat storage wall module,which can be assembled freely according to specific heating requirements.The wall module has multiple functions and overcomes the defect that the traditional heat storage heating device needs to occupy a certain indoor space.Taking an office building as the target heating object,the actual application of the valley electricity heat storage device designed in this paper has completed the analysis of economic and environmental benefits.Under the background of current peak and valley electricity prices in Jiangsu Province,this project has certain economic efficiency.When the operating year is 20 years,the net present value can reach 200,000 yuan.However,due to the relatively high initial investment of the project,the project has a long payback period.,More than 10 years.Assuming that the operating life of the system is 20 years,compared to the coal-fired heating system,the use of the valley electricity thermal storage heating system can reduce carbon dioxide emissions by 2370.1t during its full life cycle,which has good environmental benefits. |
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