Study On The Characteristics Of Indoor Thermal Environment And Critical Exhaust Volume In An Industrial Thermal Plant With Hybrid Ventilation System

At present, our country faces energy use and environmental improvement two bottleneck problems, how to reduce energy consumption and improve the quality of environment, as we must deal with challenges. As the industry product quality high grade demand and people’s material and cultural life level unceasing enhancement, the industrial plant The working environment is required more and more demanding. Usually adopt thermal pressure ventilation to eliminate indoor waste heat in the industrial thermal plant. But thermal pressure ventilation can not meet the requirement of the indoor environment in the actual plant when the outlet and inlet area are not enough or indoor residual heat is too much. In order to increase ventilation rate, people usually install mechanical ventilation devices on the roof or side wall. Thus formed hybrid ventilation system combined with thermal pressure ventilation and mechanical exhaust, but the lows of effect of this kind of hybrid ventilation are unknown.Based on industrial thermal plant, the hybrid ventilation experimental model with concentrated heat source and mechanical exhaust device at the top is set up. The changing rule of indoor vertical temperature distribution, temperature efficiency and contaminant removing efficiency in the hybrid ventilation system combined with thermal pressure ventilation and mechanical exhaust are studied by changing the residual heat, mechanical exhaust volume and natural outlet and inlet opening mode. The results show that five different natural outlet and inlet opening mode of hybrid ventilation systems all have critical exhaust volume. When the mechanical exhaust volume is less than the critical exhaust volume, increasing mechanical exhaust volume would have positive influence on temperature efficiency. When the mechanical exhaust volume is more than the critical exhaust volume, increasing mechanical exhaust volume would have negative effect on temperature efficiency. When mechanical exhaust volume is equal to the critical exhaust volume, temperature efficiency is the maximum temperature efficiency. For design of the hybrid ventilation system with natural outlet openings, the key question is to consider selecting rational mechanical exhaust volume in order to avoid natural outlet openings short circuit problem because of excessive mechanical exhaust volume. For design of the hybrid ventilation system without natural outlet openings, the key question is to consider selecting rational mechanical exhaust volume so as to avoid shock on the thermal plume by airflow from natural inlet openings because of excessive mechanical exhaust volume.On the basis of experimental research, the hybrid ventilation numerical prediction model is established, and use it to study the influence laws of indoor thermal environment and the critical exhaust volume by changing the number of exhaust fans, different of exhaust fans combined mode and mechanical exhaust volume in full size industrial thermal plant. And put forward the concept of effective ventilation rate and effective ventilation ratio to reflect short circuit problem of natural outlet openings. Effective ventilation rate is the ventilation rate which has influence on indoor thermal environment and not short circuit in the ventilation building.Effective ventilation ratio can directly reflect the natural outlet openings whether short circuit or not.When the effective ventilation ratio is less than 100% indicates that natural outlet openings are short circuit.With the increase of mechanical exhaust volume, effective ventilation rate is increasing and the effective ventilation ratio is reducing. By comparing the characteristics of hybrid ventilation of ten exhaust fans on the roof with two exhaust fans on the roof, finding that both are at the same critical exhaust volume, but the maximum temperature efficiency of ten exhaust fans is higher than two exhaust fans. Compare six exhaust fans on the roof with six exhaust fans in the side walls,finding that the first model is more likely to lead to natural outlet openings short circuit.And when the mechanical exhaust volume would have positive influence on temperature efficiency,the temperature efficiency of six exhaust fans on the roof is always greater than the temperature efficiency of six exhaust fanss in the side walls. This paper reveals the hybrid ventilation characteristics under thermal pressure ventilation combined with mechanical exhaust, which improve the indoor thermal environment and energy conservation in industrial thermal plant has a certain theoretical significance and practical application value.