Thermal Characteristics And Parameter Optimization Of Composite Phase Change Ventialation Roof

With the increase of building energy consumption,energy shortages and environmental pollution problems become more and more serious.Improving energy efficiency in building has become an important strategic measure of social development,building energy conservation is imminent.The application of phase change energy storage technology in buildings makes the envelope structure have good thermal insulation and thermal storage performance,which greatly reduces the energy consumption of building heating and air conditioning system.In this paper,composite phase change material(CPCM)was fabricated firstly,then combined with ventilation roof,the cooling storage experiment and parameter optimization of composite phase change ventilation roof(CPCVR)are carried out.The aim is to study the potential of CPCVR in building energy saving and maximize the efficacy of CPCVR.A binary eutectic mixture of Myristic acid(MA)and Tetradecanol(TD)was used as a phase change material(PCM1),expanded perlite and expanded vermiculite were used as porous adsorption building materials,then,phase change particles(PCP)were prepared by vacuum adsorption method,and DSC,SEM,FTIR and thermal cycling test were performed.Then the PCP were pressed into composite phase change plates(CPCP),and their thermal conductivity and heat storage performance were tested.The results show that the heat storage performance of expanded vermiculite composite phase change plate(CPCP2)is better than that of expanded perlite composite phase change plate(CPCP1).Combine CPCP2 with ventilation roof to construct a CPCVR experimental room.And the cold storage performance test was conducted under the natural cold storage,regularly open ventilation layer at certain time,timing cooling while regularly open ventilation layer at certain time.The results show that the use of CPCP2 effectively reduces the temperature of the outer surface of the roof;under the premise of not actively cooling,the ventilation layer is turned on at night,which can effectively reduce the indoor air peak temperature;just increasing the roof thermal inertia does not significantly increase the delay time;under the active cooling condition,the indoor phase change material(PCM2)can absorb the heat of the indoor air well,reduce the indoor air temperature and the indoor air temperature fluctuation range.Based on the fluent software,taking the Tianjin area as an example,equivalent heat capacity method was used to establish a three-dimensional unsteady CPCVR model.The internal surface temperature,the amount of heat gained and phase transition process are used as evaluation indexes to optimize and analysis the CPCVR.The results shows that under the passive strategy,the ventilation layer is opened at night,which is beneficial to the roof heat dissipation and lower inner surface temperature,reducing indoor heat gain and utilizing the latent heat;under the active strategy,the ventilation layer should not be opened all the time,which can fully utilize the cooling capacity in the active cooling.it is proper when the phase transition temperature of the CPCP2 is 32℃;for PCM2,under the premise of active cooling situation,the proper optimum phase transition temperature is 24℃,and high latent heat should coexist with high thermal conductivity;20cm is the optimal thickness of the ventilation layer;the water pipe should locate at the middle of PCM2,the closer the distance is,the lower the internal surface temperature is,and the latent heat of PCM2 is efficiently utilized.It is found that the phase change energy storage technology combined with the ventilated roof shows great potential of energy saving,and the optimization research of CPCVR provides an important basis for its application and promotion.