Dimensionless Models For Stack-Based Hybrid Ventilation And Smoke Exhaust In Multi-Story Buildings

In modern society, large-scale building makes the vertical structure be relatively common, for example, the atrium, stair, chimney and so on, and these structures drive the flow of air and smoke. Vertical structure through the accumulation of heat can improve ventilation capacity of the building and thus improve the indoor air quality, while the vertical structure of the internal heat also increases the smoke exhaust capacity of the building. Therefore, the vertical structures used for ventilation and smoke exhaust in the multi-story buildings with its advantages of energy saving, economy, simple and the certain compatibility, aroused the attention of scholars both at home and abroad.At present, domestic and foreign scholars to vertical structures used for ventilation in buildings have done a lot of researches, but most of them were about the use of stack based pure thermal pressure ventilation mode or only for single-story passive ventilation mode. However the studies of stack based ventilation for multi-story buildings were less, especially in multi-story buildings, when the shaft height is limited, if all floors use pure thermal pressure ventilation, the upper floors may be contaminated by the lower floors, but theoretical analysis method for this phenomenon is not perfect. In addition, when there is a fire in the tall building, large temperature difference between indoor and outdoor, the inside of the vertical structure can form the chimney effect. So the combination of stack based ventilation for multi-story buildings mode and the fire smoke exhaust mode can achieve composite power smoke exhaust mode, which improves the smoke exhaust capacity of the building and reduce the static pressure of the fan. Meanwhile the composite power smoke exhaust mode does not require additional power equipment, and can use exhaust fan to replace ventilation fan. So the composite power exhaust mode compared to the traditional mechanical smoke exhaust mode is more economical, simple and easy to operate. Therefore, based on the principle of conservation of energy and mass, this paper had a further study for the dimensionless models for stack-based hybrid ventilation and smoke exhaust in multi-story buildings.Firstly, this paper had carried on the dimensionless analysis for stack based hybrid ventilation and fire smoke exhaust system, and put forward the dimensionless parameter- ventilation performance indicator λ₀. Then based on the analysis of the basic theory of ventilation, got the three important design parameters-opening size of each room, neutral layer height, and the number of natural ventilation floor. As same to the ventilation theory, put forward the dimensionless parameter-exhaust performance indicator λ₀, and through the analysis of composite power smoke exhaust mode got the theoretical parameters. Secondly, based on the required ventilation performance indicator λ₀, analyzed the applicable scope of the proposed hybrid ventilation mode, other two kinds of low energy ventilation modes（displacement ventilation and stack based pure thermal pressure ventilation） and the mechanical ventilation mode, which provided a basis choose for the reasonable ventilation mode in target building. Similarly, in fire condition, based on the exhaust performance indicator λ₀, put forward the applicable scope of the smoke exhaust mode based on the indoor elevation difference, the pure thermal pressure formed by shaft smoke exhaust mode, hybrid power exhaust mode, and the purely mechanical smoke exhaust mode. The analysis of the scope for ventilation mode and smoke exhaust mode laid a foundation for the building to selected optimal ventilation and smoke exhaust mode. Finally, through the analysis of energy consumption ratio（COP） between the mechanical ventilation and hybrid ventilation mode, this article quantified the energy saving rate of the proposed ventilation scheme to find the optimization design method to the building structural parameters. And in fire condition, made the comparison between hybrid power exhaust mode and the traditional mechanical exhaust mode to the fan power needed and found that the hybrid power exhaust mode could improve smoke exhaust ability of the building and reduce the static pressure required for fan, which could save the initial investment of exhaust fan.This paper using the CFD software and three different turbulence models, verified flow field distribution of the computational domain in the target building, and made comparison between simulation and theoretical model analysis results for temperature distribution of shaft mid perpendicular, room outlet mass flow, and pressure distribution of shaft mid perpendicular. Then it proved that the proposed hybrid ventilation mode has higher accuracy and reliability.Finally, on the basis of the similarity theory, using the small size of the brine experiment, verified the flow field distribution of the proposed hybrid ventilation and the smoke exhaust scheme, thereby further verified the correctness of theoretical analysis and the rationality of the model proposed in this paper.