Experimental And Simulation Study On Resistance Characteristics Of Wind-driven Natural Ventilation In Building

Wind-driven natural ventilation, which improves indoor air environment by fully utilizing outdoor air environment, is the most effective way to reduce building energy consumption.The main factors which influence wind-driven natural ventilation include air flow around the building, building shape, window opening type, indoor resistance partition, etc. When the wind blows towards a building, the generation of air flow separation and vortexes makes the flow mechanism complex. Therefore, the investigation of the flow resistance characteristics and the ventilation rate prediction is a difficult field which researchers pay more efforts to.Our investigation focused on the prediction of wind-driven natural ventilation. Based on the existing researches, further studies were carried out to study the flow resistance characteristics of a building under wind-driven natural ventilation and to develop a model for the ventilation rate prediction.Wind tunnel test, model test for duct flow, PIV measurement and LES simulation were comprehensively used to study the flow resistance characteristics of a building under wind-driven natural ventilation and the ventilation rate prediction. Both single zone with opposite window openings and double zone with opposite window openings were investigated.Windward, leeward and indoor static pressures, as well as the ventilation rate of the room model under natural ventilation were obtained by wind tunnel tests. The tests were conducted in single-zone room, double-zone room with middle partition, double-zone room with side partition, as well as combinations of different window opening areas. Different inlet velocities were applied in each test case.Pressure differences among inlet opening, outlet opening and indoor environment, as well as the corresponding ventilation rate of the room model were obtained by duct flow tests. The tests were conducted in single-zone room, double-zone room with middle partition, double-zone room with side partition, as well as combinations of different window opening areas. Different inlet velocities were applied in each test case.Velocity vector distribution was obtained by PIV measurement. The tests were conducted in single-zone room and the combinations of different window openings.LES simulation models were established for single-zone and double-zone room under natural ventilation. The models were validated by wind tunnel tests.The influence of window opening combinations, single-zone and double-zone room with different indoor arrangements, as well as the opening ratio on ventilation rate and flow resistance was analyzed by wind tunnel tests. The characteristic of indoor static pressure distribution was analyzed for above cases. The analytical results indicate that the flow resistance is influenced by both window opening areas of windward and leeward sides when the indoor resistance along the flow direction is asymmetric. The ventilation rate increases with the increase in wind opening area. The ventilation rate increases slowly when the opening ratio increases to about 25%. For single-zone room, the indoor static pressure along flow direction increases firstly and then decreases, while the indoor static pressure distributions of both zone are uniform for double-zone room.Both the discharge coefficients of window opening and inner door opening were obtained by wind tunnel test. The analysis of discharge coefficient distribution shows that the discharge coefficients of inlet window opening and inner door opening are independent on the outlet window area; the discharge coefficients are independent on the value of Re when the Re value belongs to Self-preservation Region which satisfies the similar conditions; the discharge coefficient increases with the increase in opening ratio firstly and then decreases, the critical opening ratio is 11.1%.Based on the results of discharge coefficients and experimental data, the equivalent area was obtained. Then, the prediction models of natural ventilation rate for single-zone and double-zone room were established under experimental condition.The flow fields for different room dimensions were analyzed by LES simulation. The influence of room dimension on ventilation rate was investigated. The results shows that the difference between windward and leeward side of the room with larger room depth is larger, and owing to smaller ventilation resistance, the natural ventilation under airflow around building is stronger; for double-zone room, the ventilation rate is larger for room with middle partition, while it decreases for room with partition close to the inlet window or outlet window.The ventilation rates for rooms with different room depths or different locations of partition were simulated by LES method whose results were validated by ventilation rate prediction model obtained by experiments. The results of LES method basically agree with those of ventilation rate prediction model.The relationship among room resistance, discharge coefficients, pressure difference and ventilation rate were analyzed by duct flow experiments. The results show that when the opening ratios of inlet and outlet sides were in the range approximately 10% to 50%, the discharge coefficients are basically independent on Re; the discharge coefficient for inlet opening under cross ventilation is basically independent on the outlet opening area. The results are consistent with those of wind tunnel tests. The discharge coefficients of inlet window and inner door are different with those of wind tunnel tests.Benefit to PIV measurement, the flow field distribution for airflow through a room was clearly obtained.The main content of this investigation focused on the flow resistance characteristics, wind pressure coefficients and their characteristics, as well as ventilation rates of a building with opposite window openings for both single zone double zone were investigated. A model for the ventilation rate prediction of wind-driven ventilation was developed.The main content of this investigation focused on the flow resistance characteristics, wind pressure coefficients and their characteristics, as well as ventilation rates of a building with opposite window openings for both single zone double zone were investigated. A model for the ventilation rate prediction of wind-driven ventilation was developed.