Study Of The Theory,Preparation And Performance Of Composite Phase Change Humidity Control Materials

With the rapid development of society,the demand for energy is increasing.Energy consumption has brought about a series of environmental problems.In the whole life cycle of constructions,the energy consumed by the building is about 50%of the total energy consumption,and the energy consumption of HVAC system can account for more than 50%of the total energy consumption of buildings.The load of the HVAC system has latent heat load and sensible heat load,and the latent heat load is mainly to control the relative humidity of the indoor environment.This work attempts to achieve the purpose of energy conservation by using energy saving technology to adjust the relative humidity in the room.This work mainly includes three parts.The first is the theoretical analysis on the moisture adsorption/release phenomenon of porous material,and the moisture buffer value is analyzed.Then,the phase change humidity control materials are prepared,and the properties of the composites are tested.Finally,the performance of the materials is simulated by EnergyPlus.The adsorption process of physical adsorption and chemical adsorption is analyzed.Based on the theory of capillary condensation,the hysteresis process of the physical adsorption is analyzed,and the relationship between the hysteresis phenomenon and pore structure is analyzed respectively.A qualitative explanation about the hysteresis phenomenon of single face structure and multi curved face structure is given.The slope of the hysteresis curve caused by uniform cylindrical structure is calculated.Based on the analysis of hysteresis phenomenon,the concept of precise humidity control material is put forward,and the characteristics of the ideal fixed point humidity control material are analyzed.Using the AAO template,the theory is verified.At the same time,based on the theory of BET multi molecular layer adsorption,the formula of the moisture absorption and desorption path in the hysteresis loop is given.The moisture transfer process is analyzed when the moisture transfer coefficient and moisture capacity are not constant.The moisture buffer value is given when the surface moisture transfer coefficient is taken account.Then,considering the external relative humidity fluctuation is approximate harmonic vibration,the moisture uptake is by moisture buffer value,and the correction coefficient equation is given too.According to simulations,the moisture uptake of the gypsum board,concrete,aerated concrete and spruce are calculated,and the result is compared to that calculated by moisture buffer value.The results show that the correction coefficient is good to calculate the moisture uptake when the variation of relative humidity is harmonic vibration.Then,silica was prepared by tetraethyl orthosilicate,and the phase change material was encapsulated by blending method,and then the encapsulated phase change material and diatomite were mixed to prepare the phase change humidity control material.The microencapsulated phase change materials were prepared by sol-gel method,and phase change humidity control material were prepared by the combination of microcapsules and diatomite.Using methyl triethoxysilane,through sol-gel method,microencapsulated phase change materials were prepared,and phase change humidity control material were prepared by the combination of microcapsules and vesuvianite,zeolite and sepiolite.Through the test,the results show that the thermal properties of phase change humidity control materials are improved.The super-cooling degree decreases,and the ignition point increases.At the same time,moisture adsorption performance of each kind of composites is improved.The moisture transfer coefficient is larger,and moisture buffer value is larger than that of the porous materials.The moisture properties are better than gypsum board.The moisture buffer value of VCPCM(vesuvianite with microcapsules)reaches "good class" level.Finally,EnergyPlus is used to calculate the indoor temperature,relative humidity and energy consumption of buildings in Nanjing and Lanzhou under different climatic conditions.The calculation results show that,after using the phase change humidity control material,the fluctuation of indoor environment temperature and relative humidity is less than the control group.And the average energy conservation of the Nanjing building within five months is about 11.6%.The average energy conservation of the Lanzhou building within five months is about 28.8%.