| Phase change energy storage floor radiant cooling system is a new type of radiant cooling system constructed by adding phase change materials to the floor structure.The system can use phase change materials to store energy by using off-peak electricity which is cheaper at night,and then release the cold energy stored during the day through the phase change process for people's production and life.The system is economical and energy-saving,which can effectively transfer the load from daytime to nighttime.In addition,due to the addition of phase change materials,the indoor temperature is more stable and the thermal comfort of human is better.At present,the application of this system in practical projects at home and abroad is very few.The reason lies in the complexity of the system itself,which involves phase change energy storage technology and radiation cooling technology.The heat storage and release process of phase change materials increases the complexity of heat transfer process at the radiant terminal,which brings some difficulties to the optimization and operation control of the system.In view of this,this paper took TRNSYS software as simulation platform,a three-storey office building in Xi'an area was constructed.A composite system of phase change storage floor radiant cooling system and independent fresh air was laid in the office building.Taking indoor air temperature,average radiation temperature,floor surface heat flux density and floor surface temperature as evaluation indexes,indoor thermal environment under intermittent operation conditions was evaluated and analyzed.In addition,the system was optimized from two aspects: the design optimization of phase change materials and the optimization design of radiant terminal.The main conclusions are as follows:(1)Intermittent operation at night for 6 hours,the indoor air temperature of the office building during the second day does not exceed 26?,the floor surface does not condensate,the intermittent operation of phase change energy storage floor cooling system is feasible,which can satisfy the thermal comfort of human and standard requirements.(2)The optimization of the thickness of phase change material layer is related to the intermittent operation time.The longer the intermittent operation time is,the thickness of the phase change material layer which can stabilize the room temperature also increases.(3)When the phase change material layer is above the water supply pipes,the room temperature is more stable,the fluctuation is smaller and the energy storage ratio is larger in the daytime.Its performance is superior to the installation method of phase change material layer under the water supply pipes.(4)The larger the latent heat is,the lower the room temperature is,the greater the floor heat flux density during the day and energy storage ratio are,but the change range is less and less obvious.The study on optimization of latent heat shows that phase change materials with large latent heat should not be considered only in design,but the latent heat can be selected according to specific conditions.(5)The higher the thermal conductivity of the floor covering is,the lower the room temperature will be and the fluctuation of the room temperature will be smaller during the day.And the higher the heat flux of the floor surface will be,but the energy storage ratio will be slightly reduced.The optimization of thermal conductivity of floor coverings is not the pursuit of high thermal conductivity of floor covering materials,but to consider comprehensively according to actual conditions.(6)The larger the distance between buried pipes is,the higher the indoor temperature will be and the smaller the heat flux density on the floor surface will be.But the smaller the distance between pipes is,the smaller energy storage ratio is.Therefore,the appropriate distance between pipes should be selected according to the actual conditions. |
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