Study On Thermal-driven Natural Ventilation In Industrial Buildings With Interacting Plumes Rising From Contiguous Heat Sources

Industrial buildings are characterized by numbers of production facilities,large volumes,and huge open space inside.Amounts of heat is emitted during the production process.For such buildings,how to make use of the effect of heat plumes above the heat sources to induce and realize efficient thermal-driven natural ventilation,create a reasonable production and working environment,avoid the occurrence of production accidents,protect the health of the workers,and improve the labor productivity,has important safety implications,social and economic significance.The phenomenon that buoyancy plumes are restricted in the building due to space limitation and transformed into thermal-stratification flow within the building has been widely observed in building space.Thermal stratification in buildings has important implications for reducing building energy consumption,eliminating indoor pollutants,and improving indoor thermal comfort.Indoor thermal flow driven by thermal plumes will be restricted by the geometric framework of buildings and significant thermal stratification will be generated within the buildings in the vertical direction,which is a phenomenon widely observed in the practice.Indoor thermal stratification can contribute to reducing building energy consumption,exhausting indoor pollutants and improving indoor thermal comfort.In this paper,based on the classic “emptying-filling box model” on indoor thermal stratification research,theoretical models are deduced to quantitatively predict the key parameters(thermal stratification height,exhaust air temperature and thermal-drivenventilation rate)of the thermal-stratification flow in a naturally ventilated building with a single independent surface heat source or volume heat source.In this way can we extend the classic “emptying-filling box model” of a point heat source to the general conditions of buildings with surface heat sources or volume heat sources.The experiments and numerical simulations were carried out to verify the deduced theoretical models.Different factors on the key parameters(thermal stratification height,exhaust air temperature and thermal-driven ventilation rate)of thermal stratification flow in buildings under different single and independent heat sources were discussed.Aiming at the interacting plumes rising from contiguous heat sources widely observed in industrial buildings,especially two interacting turbulent buoyant plumes of equal strength rising from contiguous heat sources,theoretical models are deduced to quantitatively predict the key parameters(thermal stratification height,exhaust air temperature and thermal-driven ventilation rate)of the thermal-stratification flow of an enclosure containing two interacting turbulent buoyant plumes of equal strength.The experiments and numerical simulations were carried out to verify the deduced theoretical models.A threshold for the separation between two plumes is defined to determine whether the two buoyant plumes in the enclosure are interacting or independent,and simultaneous equations containing height difference between the top and bottom openings of the enclosure and effective area of the top and bottom openings of the enclosure are proposed to predict the threshold.Besides,by applying the method of virtual origin correction can we extend the theoretical models of interacting point heat sources in an enclosure to the more common cases of industrial buildings containing interacting surface heat sources or volume heat sources.For the heat sources restricted by a side boundary(a side wall or a corner),based on the principle of image theory,theoretical models are deduced to quantitatively predict the key parameters(thermal stratification height,exhaust air temperature and thermal-driven ventilation rate)of the thermal-stratification flow of an enclosure containing a buoyant plume restricted by a wall or a corner.The experiments and numerical simulations were carried out to verify the deduced theoretical models.Thresholds for the distance between the plume and the side boundary are defined todetermine whether the plume is restricted by the side boundary.Simultaneous equations containing the enclosure dimensions are proposed to predict the threshold.Besides,by applying the method of virtual origin correction can we extend the theoretical models of a restricted point heat source in an enclosure to the more common cases of industrial buildings containing restricted surface heat sources or volume heat sources.Based on the above research,cases of a typical industrial building with multiple sources heat are carried out to analyze the design calculation methods for the parameters(thermal stratification height,exhaust air temperature and thermal-driven ventilation rate)of the thermal-driven stratification flow.The principle and methods for calculating and designing the organized thermal-driven natural ventilation for an industrial building with multiple heat sources are summarized.For an industrial building containing n(n≥2)heat sources,according to the form of point heat sources,surface heat sources,and volume heat sources and whether the heat sources are interacting or restricted,calculation processes can be classified into different strategies,making full use of the building’s thermal stratification and indoor and outdoor environmental conditions,to simultaneously achieve the effective use of building energy and improve the indoor environment.By this way can we lay the foundation for creating a desirable process-production and living environment with low energy consumption and even“zero energy” in industrial buildings.