| The air distribution,the terminal of indoor ventilation and air-conditioning system,affects the thermal comfort of occupies directly.Reasonable and efficient air distribution not only consumes less energy,but also achieves a comfortable thermal environment.Nowadays,mixing ventilation and displacement ventilation are widely used,but they also have problems such as low ventilation efficiency and occupying effective space respectively.The attached ventilation can take the strengths and avoid the weaknesses of them,which is a more reasonable and efficient air distribution.However,there are few studies focused on the comparison between three ventilation methods,such as the evaluation of air distribution,and the determination of air supply velocity in winter when the attached ventilation is used.This paper analyzed a typical building space(L × W × H = 5.2 m × 3.7 m × 3.0 m)to study the effectiveness of vertical wall attached ventilation,displacement and mixing ventilation.The numerical simulation models of vertical wall attached ventilation,displacement ventilation and mixing ventilation were established respectively.Under the same building spaceand heat source conditions,a comparative analysis of the indoor air velocity,air temperature,vertical temperature gradient,and draft,ventilation efficiency,velocity and temperature unevenness coefficient,PMV-PPD index for different air distribution were made.The results of the study show that mixing,displacement and vertical wall attached ventilation are all suitable for summer air-conditioning conditions.When mixing ventilation is used for larger loads(80 W/m~2),the ventilation effect is better,while displacement ventilation is better when it used to small loads(40 W/m~2).And the applicable load range of attached ventilation is wider.There are vertical temperature gradients for displacement ventilation and attached ventilation,which are 1.5?/m and 0.6?/m,respectively.For the ventilation efficiency,mixing ventilation is close to 1.0,while displacement ventilation and attached ventilation are both greater than 1.0.The latter two have higher energy utilization efficiency.Under the same cooling load,taking the 3.0m building space as an example,displacement ventilation and attached ventilation can save cooling capacity about 40% and 20% compared to mixing ventilation,respectively.In addition,the heating conditions of mixing ventilation,displacement ventilation and attached ventilation were studied.In view of the phenomenon that the warm air is not easy to be delivered into occupied zone in mixing ventilation,the relationship between the temperature difference and the required minimum air velocity of the attached ventilation was studied.The results show that when the mixing ventilation is used for heating condition,a large amount of warm air is collected in the upper part of the room resulting in energy waste and poor indoor thermal comfort.The warm air of the displacement ventilation directly moves upward due to the action of thermal buoyancy,which cannot eliminate the space load.There is a layer of cold air lake(below 18?)with a thickness of 0.5 ? 1.0 m above the floor.Therefore,displacement ventilation is not suitable for heating conditions.The study shows that vertical wall attached ventilation can use large supply velocity,with the support of the vertical wall to send warm air to the occupied zone,which overcomes the disadvantages of displacement ventilation and mixing ventilation.In order to ensure that the warm air can be attached to the floor to move forward within the whole occupied zone(x?4.2 m),when the temperature difference between supply air and occupied zone air is between 2.0 ? ?10.0 ?,for every 1.0 ? increase in temperature difference,the minimum air supply velocity will increase by about 0.25 m/s from 2.5m/s.Finally,through the analysis of the differences between the control points and control parameters of the typical mixing,displacement ventilation and vertical wall attached ventilation,the differences between the three design methods are compared. |
PDF Full Text Request