Construction And Energy Conservation Effect Of The Combined Phase Change Thermal Storage Building Envelop

Phase change materials?PCMs?can absorb or release heat by phase transition to solve the conflict between energy supply and demand in time and space.Relying on the big phase change latent heat,PCMs can be applied in buildings to adjust the indoor temperature and improve the living comfort,which has become one of the primary means for building energy conservation.In this paper,two phase change paraffins and their binary eutectics used as phase change media and polymer methyl methacrylate?PMMA?as support material are compounded to prepare the paraffin/PMMA form-stable PCM by bulk polymerization method.The structural composition,mechanical and thermodynamic properties of the form-stable PCM are examined and analyzed,and the paraffin/PMMA board is prepared for constructing the combined phase change buliding envelope.The binary fatty acid eutectic/diatomite form-stable PCM consisting of diatomite as the carrier and fatty acid eutectic as phase change core is prepared through vacuum impregnation method.Then the form-stable PCM is directly mixed into the mortar at room temperature to obtain the phase change mortar.The combined phase change thermal storage envelope is sequentially constructed by using the phase change mortar and phase change board for thermal insulation,and its energy conservation effect in building is analyzed by both the experimental and software simulation respectively.Phase change paraffin 1 and phase change paraffin 2 is selected as the basic materials.The freezing points of these two phase change paraffin are measured by the step cooling curve method based on the lowest eutectic theory.The lowest eutectic mass ratio of the two paraffins is phase change paraffin 1 to phase change paraffin 2 equal to 78/22,and the binary phase change paraffin is prepared by melt blending method.DSC results show that the phase change temperature of binary paraffin eutectic is 18.7?and the latent heat is 119.2J/g.The result is in accordance with the result of the step-cooling curve.FT-IR analysis shows that the infrared absorption spectra of the phase change paraffin eutectic is extremely as same as those of the two single phase change paraffin.They are physically blended without any chemical reactions.The temperature damping ratios of phase change paraffin 1,phase change paraffin 2,and their eutectic mixture obtained from the heat storage/release temperature variation curve are?_p1=350%,?_p2=400%and?_p1,p2=300%,respectively.Thus,the phase change paraffin can regulate the fluctuation of indoor temperature and provide a good medium for the subsequent preparation of form-stable phase change material.Phase change paraffin/PMMA form-stable PCM was prepared by bulk polymerization using PMMA as support material,phase change paraffin and its eutectic mixture as phase change core.DSC,TG,SEM,FT-IR,density and volume expansion rate testing,mechanical properties testing,heat storage/release experiment are conducted on the form-stable PCM to analyze the thermodynamic properties,structure,phase change behavior and service performance.The results show that the phase change temperature of the form-stable PCM ranges from 14?to 25?and the latent heat 99.94 J/g to 184.7 J/g,which is comparable to the thermodynamic properties of the phase change paraffin.Due to the strong immobilization effect of PMMA on the phase change paraffin,there are no obvious thermal decomposition weight loss of paraffin below 100?,and the weight loss region of paraffin increases 25?.The SEM and FT-IR analysis results verifies the above point.Phase change paraffin and PMMA has been completely integrated with each other in the manner of physical blending and the form-stable PCM has a compact structure.The density of the form-stable PCM is mainly distributed between 0.86 and 1.06g/cm³ at room temperature and between 0.71 and1.01 g/cm³ at 80?.The volume expansion rate of the form-stable PCM at 0⁸0?is1.85%³.0%and the volume expansion coefficient is 2.48E-04⁴.21E-04,which is lower than the pure phase change paraffin.The mechanical properties test results show that the mechanical properties of the form-stable PCM are excellent at room temperature.The results of SEM and FT-IR show that the surface of the form-stable PCM is not damaged and no chemical changes are observed after 500 times accelerated thermal cycles.The phase change temperature and latent heat of the form-stable PCM has little change,which proves that the form-stable PCM has good durability.Phase change paraffin/PMMA thermal storage board was prepared by the bulk polymerization method using a self-made mold.The thermal conductivity of the phase change board is determined to be 0.12W/?m·K?using a quasi-steady state method,providing important data parameter for the subsequent simulation.The fatty acid eutectic/diatomite form-stable PCM is prepared by vacuum impregnation and added to common mortar to make the phase change mortar.In the phase change mortar,the mixing mass rario of the fatty acid eutectic/diatomite form-stable PCM is 8%?calculated by the mass fraction of cement?,and the water reducer is 0.4%.Phase change temperature and latent heat of phase change moatar is 22.2?a nd 0.84J/g,respectively.The compressive strength and flexural strength is tested to be 6.01MPa and 1.54MPa respectively,which meet the construction requirements.The combined phase change thermal storage envelope is constructed by using phase change mortar and phase change paraffin/PMMA thermal storage board and the effect of temperature control is tested.The experimental results show that the combined phase change thermal storage envelope can effectively control the indoor temperature fluctuation and enhance living comfort.DesignBuilder software is used to simulate the energy conservation effect of the combined phase change thermal storage envelope in buildings and the results show that the indoor temperature can be effectively controlled in both summer and winter.Depending on the phase change thermal storage envelope,1551kW·h of electricity would be saved in annual winter heating period which is benificial for saving energy consumption.Economic analysis indicate that the investment recovery period for adding the total cost of the combined phase change thermal storage envelope structure to residential buildings is about 32 years.Although the payback period is relatively longer,the building energy conservation effect using PCMs is better than that of the traditional insulation material and cost-efficient in the whole life cycle of buildings.It can be interpreted as one-time investment and full life cycle benefit.At the same time,it is a powerful response to the national energy conservation and emission reduction,which has positive meanings for the sustainable development of construction industry.