Comparative Analysis Of Double Layers Phase Change Material Wallboard And External Insulation Wallboard In Hot-summer And Cold-winter Zone

The shape-stabilized phase change material wallboard,which is consisted of paraffin wax,high density polyethylene and expanded graphite,can not only exert the advantage of the PCM?phase change material?that can absorb or release large amount of heat in a constant temperature during the process of phase transition,but can keep the PCM stable during the melting process.It has tremendous potential in improving the building thermal comfort and reducing the energy consumption of air conditioning?AC?.However,limited by the single phase transition temperature of one PCM,The single layer PCM wallboard can only be used in one seas on,for example,The PCM which is suitable for Summer can not be made full use of in Winter.Therefore,the double layers phase change material wallboard,which can be used for the whole year,is studied during these years.It has two layers of PCM wallboards which contain PCM with different phase transition temperatures that can be fully used both in Summer and Winter.However,the insulation wallboard,which is widely used in the traditional energy-saving building,can also be used during the whole year by reducing the room's heat gain in daytime during summer and enhance its heat preservation during winter.What is relatively lacking is the comparative analysis of these two wallboards.So comparative analysis of these two wallboards are made by comparing their abilities of improving the building thermal comfort without AC and reducing the energy consumption of AC with AC open.The influence of parameters of the double layers wallboard on the room temperature,the average melting rate of PCM,the energy provided by AC and PCM for space cooling in summer and space heating in winter,the number of starts of AC,along with the time lag to switch on AC have also been studied.The main work of this paper is as follows:Firstly,a dynamic building environment simulation model is developed based on fundamental heat balance principles.The present predicted indoor temperature and the results from the building simulation tool DeST-c are in good accordant with each other,with the maximum and mean relative errors of 3.8%and 1.3%.It ca n be used to simulate the room with insulation wallboard.Secondly,a one dimensional phase change heat transfer model id developed based on the heat capacity method.The present predicted of some chosen spots by the model and the data from the related experimental data are in good accordant with each other,with the maximum and mean relative errors is less than 2.5%and 1%respectively.It can be used to simulate the room with double layers PCM wallboard by adding this one dimensional phase change heat transfe r model to the dynamic building environment simulation model developed previously.In addition,The indoor thermal comfort of rooms with insulation wallboard and double layers PCM wallboard are compared by numerical analysis and the relationship between the indoor temperature,the average melting rate of PCM,the uncomfortableness I_sum in summer and uncooling uncomfortableness I_win in winter and the parameters of the double layers wallboard such as the thickness of the wallboard and the phase transition temperature of the PCM are also analyzed.The result shows that it performs best to reduce the uncomfortableness I_sum in summer when the thickness of the outer layer wallboard is 30 mm and the phase transition temperature of the PCM of the outer layer is 29?for it can reduce the I_sumum for 4958.8?·h,6.94%less than the I_sumum of the room with insulation wallboard.in the same way,It performs best when the thickness of the inter layer wallboard is 50 mm and the phase transition temperature of the PCM is 14?for it can reduce the I_win for4518.7?·h,4.73%less than the I_win of the room with insulation wallboard.It confirms that the double layers PCM wallboard performs better for improving the indoor thermal comfort throughout the whole year.Finally,The energy saving property of these two kind of wallboards with AC open is compared.The influence of the parameters of the double layers PCM wallboard such as the thickness of the wallboard and the phase transition temperature of the PCM on the performance of the air conditioning are considered too,such as the energy provided by AC and PCM for space cooling in summer and space heating in winter,the number of starts of AC,along with the time lag to switch on AC.The result shows that it performs best in summer when the thickness of the outer layer is 40 mm and the phase transition temperature of the PCM of the outer layer is 29?for it only spend 1033.5 kWh of the energy provided by AC and PCM for space cooling,1.34%less than the room with insulation wallboard,as well as achieve the minimum number of starts of AC in summer for 5806 times,2.65%less than the room with insulation wallboard.During the winter,it performs best when the thickness of the inter layer is50 mm and the phase transition of the PCM of the inter la yer is 15?for it only spend420.5 kWh of the energy provided by AC and PCMs for space heating,2.8%less than the room with insulation wallboard,as well as achieve the minimum number of starts of AC in winter for 2770 times,3.89%less than the room with insulation wallboard.In addition,it can reach the longest time lag to switch on AC for 21.6 min in summer,51%longer than the room with insulation wallboard,when the thickness of the outer layer is 50 mm and the phase transition temperature of the PCM of the outer layer is 29?.It can also reach the longest time lag to switch on AC for 9.94 min in winter,16.9%longer than the room with insulation wallboard,when the thickness of the inter layer is 50 mm and the phase transition temperature of the PCM of t he inter layer is 15?.It confirms that the double layers PCM wallboard performs better too for reducing the energy provided by AC throughout the whole year.From the summary of the full full thesis,it came to the conclusions that the double layers of PCM wallboard performs better for improving the indoor thermal comfort and increasing the energy saving quantity of the AC than the insulation wallboard throughout the year.However,the open times of the night ventilation,the orientations of the building,as well as the economy should be considered too for the further popularization and application of the double layers PCM wallboard in hot summer and cold winter zone.