Research On Optimization Design Of Shaped Phase Change Ventilation Roof Structure And Ventilation Strategy In Hot Summer And Cold Winter Area

With the development of all walks of life,energy pressure is becoming more and more obvious,and the energy consumption of HVAC is relatively large.In order to solve the problem of excessive energy consumption of building air conditioners,this paper takes a new type of energy-saving roof structure-shaped phase change ventilation roof-as a research object,the roof can achieve energy saving by enhancing the thermal insulation performance of the roof and reducing the energy consumption of air conditioning in summer.In this paper,three kinds of shaped phase change ventilation roof models are established by CFD numerical simulation software:outer layer shaped phase change ventilation roof,middle layer shaped phase change ventilation roof and inner layer shaped phase change ventilation roof.Under the typical outdoor climatic conditions in summer in Wuhan,the effects of phase transition temperature,phase change material thickness,cavity ventilation strategy and cavity size on the thermal performance of three roofing and the latent heat utilization rate of phase change materials were simulated by a single variable control method.The optimal working condition is determinedto realize the optimal design of the phase change layer and the ventilation layer of the phase change ventilation roof structure.The simulation results show that for the outer layer shaped phase change ventilation roof,when the thickness of the phase change material is 35mm,the phase transition temperature is 35~37°C,the ventilation speed is 2.5m/s,and the cavity radius is 40mm,the thermal insulation performance of the roof is best,the inner surface temperature of the roof is lower,and the latent heat utilization rate of the phase change material is higher;for the middle layer shaped phase change ventilated roof,the phase change material has a thickness of 25 mm,a phase transition temperature of 33 to 35°C,and a ventilation speed of 2.5 m/s,the cavity radius is40mm,which is the most optimized roof structure;for the inner layer shaped phase change ventilation roof,when the phase change material thickness is 15mm,the phase transition temperature is 29~31°C,the ventilation speed is 2.6m/s,and the cavity radius is 40mm,the roof structure is the best,the heat insulation effect is the best,and the economy is good.The energy-saving effects of three optimized phase-change ventilation roof optimization structures were analyzed under different outdoor climate conditions.The critical outdoor air temperature at which the phase change material of the outer layer,the middle layer and the inner layer shaped phase change ventilated roof begin to melt is 43°C,48°C and 49°C,respectively,and the effective action time is 372 hours,252hours and 230 hours,respectively.Comprehensive comparison of the thermal insulation performance of the three optimized structures and non-phase-change and unventilated roof,the insulation performance of the three shaped phase change ventilated roofs is superior to that of the non-phase-change and unventilated roof,and the outer layer of the shaped phase-change ventilation roof optimized structure has the best heat insulation effect,and the longest effective time in summer.Compared with non-phase-change and unventilated roof,the maximum temperature of the inner surface of the roof is reduced by up to 3.65°C,the average temperature of the inner surface of the roof is reduced by up to 1.77°C,the heat transfer per day is reduced by up to 370.49W/m~2,the attenuation coefficient is decreased by 0.053~0.172,and the delay time is increased by 1 to 5 hours.