•An empirical formula for obtaining the capture efficiency of local ventilation.•A fast method to find optimal flow rates for general and local ventilations.•The method ensures IAQ and thermal comfort at lowest cost.•The method showed energy consumption reduction of 16% in case study. The manufacturing industry consumes a large quantity of energy for ventilation to remove pollutants and heat generated during production processes. Both general and local ventilation systems have been widely used in industrial buildings for a healthy and comfortable indoor environment. However, in most industrial buildings, general and local ventilation systems were designed individually, and this will produce excessive ventilation and energy waste. Therefore, this investigation put forward a novel and fast method for simultaneously determining the optimal flow rates for general and local ventilation systems. To facilitate the calculations in this method, an empirical formula for predicting the capture efficiency of local ventilation was developed and validated. Next, based on heat and mass conservation, an empirical formula was developed to calculate the required flow rates of general and local ventilation systems. Based on the two empirical formulas above, a novel empirical formula was derived for quickly predicting the optimal flow rate. The novel ventilation design method was applied in an actual manufacturing plant to obtain the best combination of flow rates. The results predicted for the factory by our fast method were validated by computational fluid dynamics (CFD) and building energy simulation (BES). Compared to two common conditions of traditional ventilation design method, optimal combination of general and local ventilation systems consumed 15% and 20% less energy, while ensuring thermal comfort and indoor air quality. This study offers a novel method for fast and comprehensive design of general and local ventilation systems in an industrial plant.