| In recent years,Chinese construction industry has developed rapidly,and the energy consumption of building construction and operation has accounted for more than one third of the total social energy consumption,so it is urgent to save energy and reduce emissions in the construction field.There are many kinds of energy-saving measures in buildings,and night ventilation technology is a typical energy-saving measure that uses renewable resources to reduce energy consumption.Night ventilation uses the outdoor cold air at night in summer as a natural cold source to cool the indoor air,and precools the enclosure structure.During the day,the cold energy stored in the heat storage unit is used to relieve the indoor temperature rise and reduce the maximum indoor air temperature.Relevant research shows that the application of night ventilation technology can greatly reduce the indoor air temperature and save the energy consumption of refrigeration system during the next day in areas with suitable climate.However,in Chengdu,the climate is sultry and the temperature difference between day and night is small.Traditional night ventilation methods such as mixed ventilation and displacement ventilation often have poor cooling effect,and are not enough to eliminate the heat stored in the enclosure structure.Efficient and night ventilation methods need to be further studied.In order to improve the climate suitability of night ventilation,this paper based on the previous group research,explores the use of wall-mounted attached night ventilation(WANV)to improve the cooling effect of night ventilation,aiming at the climate characteristics of Chengdu.In this ventilation mode,jet flow is used to scour the west wall with high temperature at night,so as to enhance the convective heat transfer of the west wall surface,quickly take away the heat stored in the wall,improve the indoor thermal environment effectively and reduce the energy consumption of air conditioning.At present,the research on wall-mounted attached jet is mostly based on the air-conditioning condition of sending cold air in summer.When night ventilation is applied,its supply air parameters change and the regulation target of night ventilation is different from the air-conditioning condition.The existing research results are not enough to accurately explain the variation law of jet characteristic parameters under the WANV mode.This paper mainly carries out the following work:A three-dimensional numerical simulation model of non-isothermal WANV is established based on the climate characteristics of Chengdu,and the accuracy of the calculation model is verified based on previous experiments.Firstly,the relationship between the jet centerline velocity distribution under non-isothermal WANV mode and the existing formula of attached jet is discussed under the condition that the position of the slot inlet is s/b=2.It is obtained that the jet attach wall approximately the whole way at the position of s/b=2.Under this working condition,the laws of jet centerline velocity attenuation,jet spread rate and jet centerline temperature attenuation are compared and analyzed with the existing fitting formulas of wallattached jet mode,and the formula for calculating jet axis characteristic parameters under the non-isothermal WANV is revised.Discusses the comprehensive evaluation of ventilation effect by changing the supply air velocity from 2 m/s to 5 m/s,changing the opening time of ventilation from 22:00 to 03:00 at the position of s/b=2.The results show that the overall ventilation cooling effect is better when the velocity is 4 m/s and the opening time of ventilation at night is 23:00in Chengdu.Due to the limitations of the installation process or the construction of the building,there may be a situation where the the supply pipe is far away from the wall.Then,as also taking the WANV system in Chengdu in summer as an example,keep the supply air velocity at 4 m/s and the opening time of night ventilation at 23:00,and analyze the flow and heat transfer characteristics of non-isothermal WANV at different slot inlet positions s/b and different supply air angles α,and get the variation rules of jet main characteristic parameters at different s/b andα.In the two positions of s/b=2 and s/b=4,the effect of attaching the jet to the wall is better,and the jet centerline velocity decays more slowly,and the jet can remove more heat in the wall,and the vertical centieline residual temperature decays faster.When the slot inlet width is 0.04 m,the limit distance of s/b is 10 ～ 12.For the case of s/b≥6,after changing the supply air angle,the attachment effect between the jet and the wall will be enhanced.When s/b=6 and s/b=8 and the supply air angle is 30,the vertical jet centerline velocity decays more slowly,the residual temperature of the vertical jet centerline decays faster,and the cooling efficiency is higher.However,when s/b=10 and s/b=12,the cooling effect of supply air angle of 45 is better.Finally,based on the inlet slot position s/b=2,supply air velocity is 4 m/s,analyze the distribution characteristics of indoor velocity field and temperature field under different room scales while taking the WANV system in Chengdu in summer.When the room height h=2.7 m(l/h=1.1)is unchanged and the horizontal length of the room is changed to l/h=1.5 and l/h=2.0,the cooling effect after night ventilation is basically the same.When the room height is increased from 2.7 m to 3.2 m and 4.0 m,the indoor velocity distribution is more uniform,the attachment length between jet and attached wall is also increased,and the cooling effect is better. |
