Distribution Characteristics Of Indoor Oxygen Concentration And Oxygen Supply Strategies Under Natural Ventilation In Oxygen-enriched Buildings At High Altitudes

The atmospheric oxygen content of the Qinghai-Tibet Plateau is only about 60%of that of the plain area.To create a suitable indoor oxygen environment is the basic premise to ensure the life and health,efficient work and stable residence of the immigrant population who build Tibet and help Tibet.Dispersion oxygen supply is an important means to improve the indoor oxygen environment of buildings,and is gradually widely used in high-altitude hotels,Tibet cadres’turnover rooms,staff dormitories,office buildings and other civil buildings.However,in the practical application of building oxygen supply strategy in high altitude area,it is mainly based on simple calculation under ideal conditions such as confined space or complete mechanical ventilation,and rarely considers the spatial distribution characteristics of indoor oxygen concentration and oxygen enrichment effect under the actual situation of building natural ventilation,which brings severe challenges to the development and popularization of diffuse oxygen supply technology.In this study,aiming at the non-uniformity of oxygen concentration distribution in the room with natural ventilation in high altitude area,the ratio of oxygen concentration in different indoor positions to the average of indoor oxygen concentration was taken as the characteristic parameter to characterize the non-uniformity of oxygen enrichment in the room.Through CFD numerical simulation and experimental test verification,the characteristics of oxygen diffusion and oxygen distribution in the room with natural ventilation were studied.Firstly,the reasonable natural ventilation level was set according to the meteorological conditions of high altitude area,and the factors affecting the spatial distribution of oxygen concentration under the condition of natural ventilation were determined according to the principle of oxygen balance between indoor and outdoor oxygen enrichment;Secondly,the quantitative effect of natural ventilation on oxygen diffusion and concentration distribution in oxygen enriched rooms was analyzed by response surface methodology,revealing the law of oxygen diffusion and distribution in buildings at high altitude,and the accuracy of the simulation model was verified by experiments.Then,according to the quantitative results of oxygen concentration distribution,combined with the comprehensive factors such as enclosure tightness,indoor oxygen supply demand and indoor personnel distribution,the scientific and reasonable oxygen supply and ventilation regulation mode,the calculation method of oxygen load considering oxygen distribution and the diffusion oxygen supply strategy in high altitude areas were proposed to guide the indoor oxygen supply in plateau areas.The main results of this study are as follows:（1）No matter heat pressure or wind pressure is dominant,when the room shape index F^1/2/H is 1.65,the oxygen diffusion in the center of the room is the slowest;Natural ventilation dominated by wind pressure is more likely to cause uneven indoor oxygen diffusion rate and oxygen concentration distribution space than natural ventilation dominated by hot pressure.The smaller the effective depth and the farther the distance from the ventilation outlet,the slower the oxygen diffusion rate will be.（2）the oxygen distribution under wind-driven natural ventilation was more nonuniform than that under buoyancy-driven natural ventilation,with the ratio of local oxygen concentration to overall-mean oxygen concentration,the k value,between 0.8and 1.3 under wind-driven natural ventilation and between 0.9 and 1.1 under buoyancy-driven natural ventilation.The influence of natural ventilation on oxygen concentration was not significant in the jet direction from the oxygen outlet under wind-driven natural ventilation.The non-uniformity of oxygen distribution was prominent in depth and width directions under TCO mode,and in height direction under both LCO and OCO modes.（3）Under wind-driven natural ventilation,TCO mode was recommended for occupants in sitting or standing posture and centralized location with x/L and y/Y both between 0.4–0.6 when the incoming wind speed kept low by`C_ibetween 0.250–0.270;and LCO mode was recommended for occupant in lying posture or wind speed kept high by （?）₁ lower than 0.230.Under buoyancy-driven natural ventilation,OCO mode was recommended when the indoor and outdoor temperature difference was large by （?）₁ between 0.210–0.225;LCO mode was recommended when （?）₁ higher than 0.240.（4）An oxygen load calculation method was proposed based on oxygen balance equation with consideration of the non-uniformity of oxygen concentration distribution in this study,so as to supply oxygen to personnel occupied zone more accurately.This study defined the reasonable natural ventilation level or natural ventilation intensity in the actual situation of the building according to the meteorological conditions;Combined with outdoor meteorological factors and building factors,the oxygen migration path of buildings in high altitude area was analyzed,and the formation mechanism of building oxygen load was revealed;The quantitative distribution results of oxygen concentration under different outdoor conditions,different oxygen supply modes,different oxygen source locations and different room shapes were formed to provide the basis for the calculation of oxygen load in building environment;Finally,combined with the actual meteorological conditions,room types and other factors,according to the typical indoor personnel distribution situation,this paper put forward the indoor oxygen environment regulation strategy of plateau buildings,which provided more scientific,reasonable,efficient and energy-saving technology and strategy for building oxygen supply under natural ventilation conditions,and provided guidance for improving the oxygen supply efficiency of buildings in high altitude areas and reducing the energy consumption of oxygen supply system.