Integral ventilation and local ventilation
Total ventilation, also known as dilution ventilation, is to ventilate the whole workshop or room, so as to change the indoor temperature, humidity and the diluted concentration of harmful substances, and continuously discharge the polluted air outside, so as to make the air environment in the working area meet the requirements of health standards. According to the different airflow directions, total ventilation can be divided into total air supply and total exhaust. According to different ventilation modes, comprehensive ventilation can be divided into natural ventilation, mechanical ventilation or the combination of natural ventilation and mechanical ventilation. Comprehensive ventilation is to ventilate the whole room when the source of harmful substances is not fixed, or when the concentration of harmful substances still exceeds the standard after local ventilation. According to the different action mechanism, it can be divided into: (1) dilution ventilation, also known as mixed ventilation, that is, air with lower concentration than indoor pollutants is mixed with indoor air to reduce indoor pollutant concentration and make it meet the hygiene requirements. (2) Displacement ventilation displacement ventilation system originated in northern Europe and has been applied in China. In the displacement ventilation system, fresh cold air is sent from the bottom of the room at a very low speed, and the temperature difference of supply air is only 2-4℃. Because of its high density, fresh air penetrates into the bottom of the room like water. Convective airflow caused by heat source makes a vertical temperature gradient in the room, and the airflow rises slowly, leaving the work area, pushing the residual heat and pollutants to the top of the room, and finally directly discharging from the exhaust port set on the ceiling or the top of the room. Indoor air flows like a piston, so that pollutants are discharged from the top of the room with the airflow, and the working area is basically in the air, that is, the concentration of pollutants in the working area is roughly equal to that of air, which is the biggest difference between displacement ventilation and traditional dilution ventilation. Obviously, displacement ventilation is much better than dilution ventilation.
Local ventilation is to ventilate the local area of the room to control the diffusion of pollutants in the local area, or to obtain a better air environment in the local area, that is, local exhaust and local air supply. For example, the exhaust of kitchen stoves is a typical local exhaust. The scope of local ventilation is limited to places where harmful substances are concentrated, or the ventilation mode in local areas where workers often move, which is called local ventilation. Local ventilation system can be divided into local air supply and local air exhaust. Both of them use local airflow to prevent the workplace from being polluted by harmful substances and improve the air conditions in the workplace. The scope of local ventilation is limited to places where harmful substances are concentrated, or the ventilation mode in local areas where workers often move, which is called local ventilation. Local ventilation system can be divided into local air supply and local air exhaust. Both of them use local airflow to prevent the workplace from being polluted by harmful substances and improve the air conditions in the workplace.
Mechanical ventilation and natural ventilation
Mechanical ventilation and natural ventilation are common forms of ventilation in civil buildings, but mechanical ventilation system relies on fans to provide the pressure needed for airflow, while natural ventilation relies on wind pressure and hot pressing to make airflow flow. Mechanical ventilation system includes mechanical air intake system and mechanical exhaust system, local air supply and local exhaust system.
Natural ventilation is the most economical way to obtain large air volume without consuming electricity, and should be used as much as possible. The principle of natural ventilation has been mentioned in Chapter 7, so I won't go into details. It should be noted that the function of natural ventilation is complex and changeable, especially for high-rise buildings and buildings with complex shapes. It is not the windward side that will get wind, but the leeward side will definitely get exhaust. For high-rise buildings, hot pressing and wind pressure play a great role in natural ventilation. In the calculation of heat load, attention should be paid to the increase of heat consumption of cold air infiltration and cold air intrusion when the external door is opened. In addition, due to the existence of hot pressure and wind pressure, elevator shafts and stairwells in high-rise buildings will produce "stack effect", which is very unfavorable for fire prevention and smoke exhaust.
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The main sources of indoor pollutants in civil buildings exist in all aspects, including people and their activities; Building materials; Pets; Furniture, daily necessities, etc. Harmful factors of indoor pollutants include toxicity; Radioactivity; Potential factors leading to colds, allergies, dermatitis, etc. ; Produce an unpleasant smell, etc. Ventilation and air conditioning technology is developing from solving the regulation of air environment to comprehensive regulation of internal space environment quality. The application of ventilation and air conditioning will be more and more extensive, and the development prospect of ventilation and air conditioning technology is beautiful and broad.
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