Study On The Characteristics Of Solar Air Collector-hollow Interior Wall Heating System

Solar energy heating has a broad application prospect in the cold region of the Qinghai-Tibet Plateau with high altitude,low temperature,and rich solar energy resource.Its energy-saving,ecological and environmental benefits are very significant.The heating load of ordinary residential building is small during the daytime and large during the nighttime.And there is a clear contradiction between the solar energy heating and indoor heating load.Therefore,solar energy heating is often used in combination with a thermal storage system.At present,solar energy heating is mostly combined with external walls,and passive technology is the main one.However,as the heat storage structure,the external walls have large heat losses and low indoor effective heat utilization.A new heating system combining the ventilated hollow interior wall with a solar air collector(SAC-HIW heating system)is presented in this paper.The interior wall in the system can store the heat collected by the solar air collector during the daytime and release it to the room during the nighttime,which increases the indoor air temperature at night and reduce the heating load.For the complex three-dimensional unsteady heat transfer process of the SAC-HIW heating system,this paper divides the air passage into several areas according to the discrete mathematical thought.The heat transfer process is simulated by using the multi-area ZoneMixing ventilation model in the software-EnergyPlus.The accuracy of the method is verified by the 3D numerical simulation results of Fluent and experimental data.The ordinary residential building equipped with the SAC-HIW heating system in the cold region is taken as the object,and the adaptability of the system is analyzed in this paper.Compared with the room without this system and the traditional application of the solar air collector,this system can increase the nighttime minimum indoor air temperature by 6.5?and 3.2?respectively in a typical day.The SAC-HIW heating system effectively improves the indoor thermal comfort.When combined with auxiliary heating equipment to ensure the indoor minimum temperature at 12?,the nighttime heating load is reduced by71.4%and 68.5%during the heating period,respectively and ensure the indoor minimum temperature at 15?,the reduction is 56.8%and 51.6%,respectively.The SAC-HIW heating system has more energy saving potential.On this basis,this paper further studies the influence factors of the system performance,including the ventilated hollow interior wall material and thickness,window-wall ratio,circulating air volume,solar radiation intensity,outdoor air temperature and the performance of the external protective structure,etc.For the common internal wall material in the project,when the thickness of the material is less than 120mm,the thickness of the internal wall is larger,and the indoor minimum temperature is higher.The heat storage of the internal wall is not the decisive factor of indoor minimum temperature,and the material with a longer time constant and a large thermal inertia should be selected as the ventilated hollow interior wall material.The increase of the southward window-wall ratio can significantly improve the indoor minimum temperature,but it also reduces the area of the collector and its heat collection.The best southward window-wall ratio should be between 0.3 and 0.4.The circulating air volume also affects the convection heat transfer coefficient on the inner surface of the ventilated hollow interior wall and the collector outlet air temperature.The optimal circulating air volume of the collector is 300~500m~3/h.The greater the solar radiation intensity,the better the effect of the SAC-HIW heating system,but the outdoor air temperature has little effect on the effect of the system.The effect of the SAC-HIW heating system can be improved by increasing the performance of the external protective structure.In order to realize the application of the SAC-HIW heating system,this paper applies the system to the passive student dormitory-Sweet Nest NO.1.Compared with the original design scheme,the system can increase the nighttime minimum indoor air temperature by2.6°C.The indoor air temperature higher than 12?at night time can reach 77.8%,higher than 15?can reach 47.6%during the heating period.The indoor air temperature and thermal comfort are obviously improved.So this system has a good promotional value for ordinary residential buildings in the cold region of the Qinghai-Tibet Plateau which is rich in solar energy.