Research On Thermal Performance Of New Type Building Envelope Structure Coordinated By Heat Reflective Coating And Phase Change Material

With the continuous improvement of people's living standards and the requirements for the comfort of living environment,the proportion of building energy consumption in total social energy consumption has increased in recent years.The thermal insulation effect of a building directly affects the magnitude of heat loss.In the hot summer,due to strong solar radiation,roofs and walls are the main bridges for heat transfer,which results in great heat gain and increases the cost of air conditioning.Cold roof technology and latent thermal energy storage technology?LTES?are two potential passive cooling technologies.Combining the two technologies can simultaneously improve insulation and thermal storage capacity of the buildings,thereby improving indoor comfort and reducing air conditioning energy consumption,and then realize building energy conservation.This paper is devoted to the combination of shape stable and low-cost composite phase change materials with heat reflective coating and cold roof technology to build a new building envelope structure.Besides,the thermal performance of the building is also studied and optimized.First,cool roof technology and LTES were combined together to apply to the wall.In the experiment,SUPER THERM coating with high reflectivity and high emissivity was employed as heat reflective coatings?HRCs?,and RT31/EG composite was exploited as experimental phase change materials?PCMs?.15 kinds of combination modes of HRCs and PCMs were constructed to test the temperature rise of the wall under 90 minutes'illumination.After then,the effect of thermal conductivity of PCMs,thickness of PCM layers as well as insulation air gap on the thermal performance of the wall were investigated.The results show that applying HRC and PCM these two cooling function materials to the wall can narrow indoor temperature fluctuation,but there must be a thermal insulation layer between heat reflection and heat storage to weaken the heat transfer of the PCM and enhance its thermal storage,thus maximizing the effect of the two materials.Among them,the structure that coats the HRC on the exterior wall and fills the PCM in the inner cavity reduces the indoor temperature of the reference room by 4.7?,and it is the optimal case.In addition,replacing RT31/EG composite with RT31/Si O₂composite with low thermal conductivity can decline the room temperature by 3.6-5.6?.Moreover,increasing the thickness of the air layer and PCM reduces the indoor temperature to 1.9-9.6?,but the amplitude will not obvious while exceeding 8 mm.Next,these two technologies were used in the roof,and the energy-saving effect of the cool PCM roof under whole day solar radiation condition was explored.In the experiment,Ca Cl₂·6H₂O/EP composite with low thermal conductivity was prepared for the experiment.Four types of roofs were constructed-a traditional roof,cool roof,PCM roof,and cool PCM roof to simulate their cooling performance and energy saving effect under the Ningxia summer climate.Furthermore,cool PCM roof has been optimized to obtain the most suitable position of the PCM and optimal thickness of heat insulation and heat storage.The results show that compared with traditional roof,the other three types of roofs can effectively reduce indoor temperature fluctuation.Among them,cool PCM roof have the best effect,which can reduce the indoor peak temperature of 6.6? and save energy consumption up to 52.9%.Comapring with middle and top layer,the case when PCM locates in internal layer cuts down the peak indoor temperature by 1.2? and 0.7? respectively.There is no doubt that the thicker the PCM and the insulation layer are,the stronger the heat insulation.However,considering the building cost and energy consumption,the 5 mm PCM and 20 mm insulation are sufficient to ensure that the building maintains within a comfortable range of 22-28? throughout the day.In summary,the new type energy-saving cool PCM roof has excellent thermal storage and insulation capabilities,which provides a broad application prospect for the effective combination of cold roof technology and LTES.