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4 Types of ventilation systems you should know

4 Types of ventilation systems you should know


4 Types of ventilation systems you should know

A ventilation system in a building may perform only one or a few of these tasks. Among them, the function of using ventilation to remove indoor waste heat and humidity is limited, and it is limited by the state of the outdoor air.

Classification by ventilation power: natural ventilation, mechanical ventilation; according to the scope of ventilation services: comprehensive ventilation, partial ventilation; classification by airflow direction: air supply, exhaust (smoke).


ventilation systems

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Natural ventilation

Natural ventilation refers to a ventilation method that uses the heat pressure caused by the density difference between the inside and outside of the building or the wind pressure caused by outdoor atmospheric movement to introduce fresh outdoor air to achieve ventilation. It does not consume mechanical power, and at the same time, it can obtain a huge ventilation volume under suitable conditions. It is an economical ventilation method. Natural ventilation is widely used in general residential buildings, ordinary office buildings, and industrial plants (especially high-temperature workshops), and can economically and effectively meet the air quality requirements of indoor personnel and the general requirements of production processes.

Features: Reduce energy consumption; improve space utilization; improve comfort; economical and no equipment noise; rely on natural forces; restricted by outdoor air quality.


Technical principle:


1. Natural ventilation under wind pressure. When the wind blows towards the building, it will generate a positive pressure on the windward side of the building because it is blocked by the building. At the same time, the airflow bypasses the sides and back of the building, creating negative pressure at the corresponding locations. Wind pressure ventilation is to use the pressure difference between the windward side and the leeward side of the building to achieve air circulation. Climatic factors that affect wind pressure ventilation include: air temperature, relative humidity, and air velocity. The area of the air inlet and outlet of the building, the position of the opening, and the angle between the wind direction and the opening affect the effect of wind pressure and ventilation.


2. Natural ventilation under heat and pressure. Heat stress is caused by the temperature difference between indoor and outdoor air. Due to the temperature difference, the indoor and outdoor density difference is generated, and a pressure gradient appears along the vertical direction of the building wall. If the temperature inside is higher than outside, there will be a higher pressure in the upper part of the building and a lower pressure in the lower part. When orifices are present at these locations, air enters through the lower openings and exits the upper. If the indoor temperature is lower than the outdoor temperature, the airflow is in the opposite direction. That is, the air density caused by the temperature difference between indoor and outdoor air and the height difference between the air inlet and outlet are used to achieve ventilation.


3. Natural ventilation under the joint action of wind pressure and heat pressure. Natural ventilation in actual buildings is the result of the joint action of wind pressure and thermal pressure, and the two effects sometimes reinforce each other and sometimes cancel each other out. Because wind pressure is affected by factors such as weather, outdoor wind direction, building shape, and surrounding environment, when wind pressure and thermal pressure act together, there is not a simple linear relationship.


Mechanical ventilation

Relying on the wind pressure and air volume provided by the fan, the outdoor fresh air or treated air can be effectively sent to any workplace in the building through the pipeline and the air supply and exhaust system; The exhausted air is discharged to the outside in time, or sent to the purification device for treatment and then discharged. This method of ventilation is called mechanical ventilation.

Features: Relying on the force generated by the fan to force the indoor and outdoor air circulation, it can be determined according to the actual results that the ventilation effect will not be affected, and the air volume can also be changed by adjusting the transposition.


According to the size of the scope of action and the difference in ventilation function, mechanical ventilation can be divided into two forms: general ventilation and local ventilation.


Comprehensive ventilation

 comprehensive ventilation, also known as dilution ventilation, is to ventilate the entire room, use the fresh air sent into the room to dilute the concentration of harmful substances in the whole room to below the allowable concentration of the hygienic standard, and at the same time remove the polluted dirt in the room. The air is discharged to the outdoor atmosphere directly or after purification. Comprehensive ventilation includes comprehensive air supply and comprehensive exhaust, both of which can be used at the same time or separately.

Local ventilation: refers to the use of local airflow, so that local locations are free from pollution and form a good air environment. Local ventilation includes local air supply and local exhaust.


Comprehensive ventilation is to ventilate the whole room, use the fresh air sent into the room to dilute the concentration of harmful substances in the room to below the allowable concentration of the national health standard, and at the same time discharge the polluted dirty air directly or after purification. Get out into the atmosphere. Comprehensive ventilation can improve the indoor environment of the entire room, but consumes a large amount of air and wastes energy.


Local ventilation

Local ventilation is the use of local airflow, so that the place where personnel work is not polluted by harmful substances, so as to create a good local working environment. Local ventilation has the advantages of good ventilation effect and air volume saving. It is suitable for large-scale workshops, especially high-temperature workshops with a large amount of waste heat, and it is used when comprehensive ventilation cannot ensure that all places in the room can reach a suitable level. However, the design of local ventilation requires accurate calculation, otherwise the degree of ventilation cannot be guaranteed.

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