Ventilation equipment is the facilities to complete the ventilation work in the building. It is divided into natural ventilation and mechanical ventilation, also known as ventilation. Natural ventilation is a way of ventilation and gas transmission to indoor, mine or roadway areas by using natural wind pressure, air temperature difference and air density difference. Mechanical ventilation relies on the air pressure and air volume provided by the fan to send outdoor fresh air or treated air to any workplace of the building through the pipeline and air supply and exhaust outlet system; Or discharge the polluted air in the building to the outside in time, or send it to the purification device for treatment, and then discharge it after passing the treatment.
working principle
Natural ventilation relies on the wind pressure caused by outdoor wind and the thermal pressure caused by the temperature difference between indoor and outdoor air to promote air flow and make the indoor and outdoor air exchange of the building. Natural ventilation can ensure that the building interior can obtain fresh air, take away excess heat, do not need to consume power, save energy, save equipment investment and operation cost, so it is an economic and effective ventilation method.
However, natural ventilation is closely related to outdoor meteorological conditions, which is difficult to be controlled manually. Wind pressure ventilation using wind pressure as driving force and hot pressure ventilation using hot pressure as driving force. When the outdoor natural wind blows to the building, a positive pressure area is formed on the windward side and a negative pressure area is formed on the leeward side of the building. The pressure difference between the two is used for indoor ventilation, which is wind pressure ventilation. Hot pressure ventilation is the air flow caused by the density difference of air caused by the temperature difference between indoor and outdoor: when the indoor air temperature is higher than outdoor, the outdoor air enters the room from the lower part of the building and is discharged from the upper part of the building to the outside; When the outdoor temperature is higher than the indoor temperature, the air flow direction is opposite. In most cases, wind pressure and thermal pressure work at the same time. At this time, the flow direction of mainstream air is determined by the action direction and strength comparison of the two driving forces.
Mechanical ventilation is driven by fan to cause air flow. Mechanical ventilation is not limited by natural conditions. It can supply and exhaust air as needed to obtain stable ventilation effect.
The outdoor air enters the air supply room through the louver. The air supply room is equipped with air filter for purifying the air and air heater for heating the air. After purification and heating, the air is pressurized by the fan and transported to the air supply grille (i.e. air outlet) in the room through the air duct, and then distributed to each room to mix with the indoor air. Sometimes, the exhaust air is sucked into the return air duct through the lower exhaust outlet, returns to the air supply room, and continues to be used after mixing with outdoor fresh air. The purpose of using circulating air is to ensure that the indoor temperature and wind speed are evenly distributed on the premise of energy saving. The size of air supply and exhaust volume and the layout of air supply and exhaust outlets have a great impact on the distribution of air temperature, humidity, speed and pollutant concentration in the ventilation room. Reasonable arrangement of air supply and exhaust outlets and distribution of air supply and exhaust volume is called indoor air distribution.
application
Natural ventilation can ensure that the building interior can obtain fresh air, take away excess heat, do not need to consume power, save energy, save equipment investment and operation cost, so it is an economic and effective ventilation method. However, natural ventilation is closely related to outdoor meteorological conditions, which is difficult to be controlled manually.
Mechanical ventilation has the following advantages: ① the air entering the room can be treated in advance (heating, cooling, drying and humidification) to make the temperature and humidity meet the sanitary requirements. ② Discharge the air of the workshop, purify the dust or harmful gas, recover valuable raw materials and reduce pollution. ③ The fresh air can be distributed to each specific place according to the characteristics of process layout, the air volume can be distributed according to the needs, and the waste gas can be directly discharged from the work place. However, the equipment and maintenance cost of mechanical ventilation are large. Therefore, mechanical ventilation must be adopted on the basis of making full use of natural ventilation, and local mechanical ventilation should be considered first.
Mechanical ventilation and natural ventilation are often used in some occasions. Some rooms have high requirements for the air environment, and the surrounding air is not allowed to flow in. The mechanical air supply volume of these rooms should be greater than the mechanical exhaust volume (or only mechanical air supply, all natural exhaust) to make the indoor pressure greater than the atmospheric pressure. Excess indoor air will flow to the outside through doors, windows and other gaps. For some rooms with serious pollution (such as toilet, kitchen, etc.), in order to prevent the dirty air from flowing into the surrounding space, the indoor pressure should be less than the atmospheric pressure, so that the dirty air in the room will not flow outdoors.
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