Analysis Of The Impinging Jet Ventilation And Mixing Ventilation On Warm-air Heating Systems In Large-height Spaces

When warm air is used for room heating in winter,a large amount of heat will be gathered in the upper part of the space and can not be utilized effectively,resulting in unnecessary waste of energy because of the influence of thermal buoyancy.With the rapid development of urbanlization in China,more and more buildings with large-height space are used in urban areas,and heating energy waste is even more serious in these buildings with high internal space.For large-height space heating in winter season,the air conditioning area is only in the lower part of the space which is the main working or living zone of occupants,and there is no need for heating in the upper zone.However,the temperature in the upper part of the room will be too high because of the thermal buoyancy,so the reasonable airflow organization is one of the main factors influencing heating energy comsumption in large-height spaces,and more heating energy will be wasted in such spaces than those in regular rooms.Therefore,proper and reasonable air flow patterns play important roles for reducing energy comsumption in such spaces.Generally,the most popular ventilation strategy is mixing ventilation(MV),but air flow patterns by MV is difficult to be used to eliminate the thermal stratification in rooms be heated.Impinging jet ventilation(IJV)is an alternative and novel ventilation strategy,it can take the new air to the work area directly from the lower part of indoor and combined the advantages of displacement ventilation and mixed ventilation.The air distribution of IJV can reduce or eliminate the phenomenon of indoor thermal stratification theoretically,and increase the utilization ratio of heating energy.But most of the studies are confined to the summer,and the object is the conventional narrow space,winter heating research for Large-Height Space is rarely involved,especially the comparative study for MV and IJV.To this end,this paper makes a comparative study on the heating effect of MV and IJV with different characteristics.There are many factors influencing the heating airflow of MV in large-height space,such as: air return position,air supply angle,air parameters and the location of the inlet.Numerical simulations have been carried out to compare the heating characteristics between IJV and MV with different height of inlet.The results show that large air feed angle and lower air inlet position can effectively improve the energy utilization efficiency of the MV,but the thermal comfort in working zone can not be maintained,and occupant's thermal sensation will be beyond the acceptable range,especially when the air supply angle is at a large value.The increases of the inlet location can effectively improve the indoor comfort with a small air supply angle,but the energy utilization will be decreased,the energy utilization of large supply angle is hardly affected by the location of the inlet,the supply of wind energy can always be used effectively,but the indoor comfort can not be improved.The upper return and the under return to the energy utilization effectiveness and indoor comfort are almost the same when the air supply inlet is low,air supply energy can be effectively utilized,but there may be a risk of draught to the occupants.Most part of the working zone of the two air return locations are fall into an acceptable range.However,when lower the position of the inlet,the energy utilization becomes better,and the higher of the inlet position,the higher the energy efficiency of the bottom air return mode of the MV.The temperature distribution of IJV room is relative uniform compared to other ventilation strategies,the mixing of warm air in the room and the energy utilization efficiency is obviously better than that in MV,and the higher of the inlet position of MV,the more obvious of energy usage advantage of IJV comparing to that in MV.The draught risk of IJV is higher than MV,but is still in an acceptable range.The higher height of MV inlet,the smaller draught risk,but this is at the expense of high energy consumption.Therefore,IJV can achieve energy saving and comfort requirements at the same time when in a large-height space which have no special restrictions on draught risk and the height of MV inlet is inappropriate to be too low.