| The air environment of large space is mainly created by ventilation and air conditioning system,and the airflow organization form is an important and direct factor affecting the effect of ventilation and air conditioning.At present,there are many problems such as low ventilation efficiency and low air supply speed when the traditional air distribution is applied under the heating mode of large space buildings.As an alternative,column attached ventilation?CAV?is suitable for local conditions and combines with the ubiquitous columns in large spaces.The hot air flow overcomes the upward buoyancy effect under the action of"traction support"of the column,and is efficiently sent to the lower working area to achieve better heating effect with less energy consumption.In this paper,the characteristics and effects of airflow distribution in column attached ventilation under heating mode are studied.In this paper,the theory of column attached ventilation under heating mode is studied.Based on the scale model,the visualization experiments were carried out to verify the feasibility of column attached ventilation,and the three-dimensional velocity field test was performed to verify the numerical simulation model.Through numerical simulation,the air flow characteristics under cooling and heating modes are compared,and the position of the air return is optimized.Evaluate the effect from four aspects:flow field distribution,thermal comfort,air supply effectiveness,and pollutant removal effectiveness.The research on air distribution characteristics shows that the air flow pattern in heating mode is obviously different from that in cooling mode.It is necessary to consider the effect of buoyancy on airflow diffusion and introduce the dimensionless criterion number Ar,which comprehensively reflects the inertial force and buoyancy force.When Ar?2.241×10-3,the thermal jet can flow to the lower part of the space and hit the ground to realize Extended Coanda Effect,forming an effective secondary attachment phenomenon.In the process of decreasing Ar,the effect of inertial force is obviously improved.The heat removal efficiency is basically increasing,and the maximum value is approximately 1.158.When 0.6×10-3?Ar?5.6×10-3,the contaminant removal efficiency of CAV basically fluctuates around 1.In terms of the effect of ventilation,the study found that when mixed ventilation?MV?is used for heating,there will be obvious thermal stratification in the direction of space height,resulting in high temperature in the upper part and low temperature in the lower part of the space.In CAV mode,the thermal stratification phenomenon in the space height direction is not obvious,and the heat removal efficiency is 1.037,which saves 14.18%of energy compared with MV.In CAV mode,the air age of the working area is 298.9s,which is much smaller than that of mixed ventilation.At the same time,the CAV air jet can be attached to the ground to diffuse the flow around,and the distribution of"air lake"formed by the diffuse flow is similar to the displacement ventilation mode.The CO2 concentration at a height of 1.7m in the human breathing zone is only 458.67ppm,which can effectively improve the thermal comfort.When the position of the outlet is lowered,the enhanced suction effect aggravates the air disturbance in the lower area of the large space,and the guidance of the air flow makes the air flow more regular.Both heat removal efficiency and contaminant removal efficiency are slightly improved.When the position where the cylinder is attached to the ventilation return port is at 0.25H,the heat removal efficiency is increased by 5.6%and the contaminant removal efficiency is increased by 8.9%.The position of the return air inlet has little effect on the age of the air,ADPI,PMV,DR,and CO2 distribution,and is at a relatively high level.This paper gives the flow characteristics and effects of the air flow of CAV under heating mode,and further perfects the theoretical system from cooling to heating.It lays a theoretical foundation for the engineering design of column attached ventilation. |
PDF Full Text Request