| With the improvement of people’s living standards, indoor air quality of existing ventilation strategy cannot meet the needs of modern people. Meanwhile, because of the growing global energy crisis situation, people expect to seek a ventilation strategy not only can ensure the air quality but also is an energy saving system. At present, the most popular ventilation strategy in our country is mixing ventilation(MV) system, and some other ventilation systems for buildings of different functions, such as displacement ventilation system, UFAD system and so on. The principle of traditional MV system is treating fresh air into required temperature and humidity, then mixed with indoor polluted air to dilute pollution, at last exhausting the diluted air. MV system has low ventilation efficiency and low energy efficiency, therefore it’s more and more difficult to meet the demand of building environment. In displacement ventilation system, the fresh air is suppled directly to the lower part of the room, and the polluted air is discharged to the outdoors at the ceiling level without mixing with the fresh air due to the principle of air stratification. The indoor air quality is improved greatly compared with MV system, but displacement ventilation system cannot be used in winter due to low supply momentum.Impinging jet ventilation(IJV) originated in Sweden in the late 1990 s not only can improve the indoor air quality with high efficiency, but also can be used in winter to overcome the disadvantage of displacement ventilation system. However, existing researches of IJV mostly focused on cooling. Therefore, it’s greatly necessary to research about IJV used in heating situation.Based on previous study, cold air infiltration is rarely considered in simulation calculation and research focused on influences of indoor thermal environment. Actually cold air infiltration through the door has significant influence on thermal environment and energy consumption of heating room, and this kind of room is common in life. Therefore, focused on heating room with obvious cold air infiltration, this paper makes cold air infiltration as the basic variable to study the heating effect and energy consumption in IJV system and MV system using CFD simulations.The results show that: due to the cold air infiltration, the heating room cannot become warmer immediately after air conditioner is opened, the average temperature of heating room needs some time to show an obviously increase; when the air conditioner is closed, temperature of the lower part of the room shows a great decrease, however, the higher part of the room is unaffected almostly, the average temperature appears obvious decrease after some time. In addition, as time goes on, temperature variety on planes with different height tend to be same in IJV system, but it’s tend to be opposite in MV system. The reason of this phenomenon is that the style of air supply and exhaust selected in MV system is top-top, when the room is heated by high temperature, considerable hot air is collected in higher part of room, therefore temperature difference between upper and lower part is increased. When the temperature of supplied air is same as indoor air, supplied air and indoor air are mixed well, the temperature difference between upper and lower part is reduced.According to the analysis of energy consumption, the temperature difference between the upper and the lower part of the MV room is larger than IJV room under the same situation of cold air infiltration. This shows that more heat gathered in the upper part of the MV room, which is one of the reasons that lead to the waste of energy. Additionally, the mixing extent of indoor air in IJV room is larger than MV room with obviously cold air infiltration. With greater cold air infiltration and more moderate outdoor temperature, the energy saving effection of IJV will be more obvious. |
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