The air purification treatment in the clean room is very important, and its first task is to control the particulates and bacteria suspended in the indoor air to ensure that the air cleanliness of the production environment meets the process requirements. To achieve this, there are three main air purification measures that are commonly employed:
(Recommended reading: Decoration design requirements for medical device clean workshops.
First of all, air filtration is the key link. The high-efficiency filter can effectively control the cleanliness of all the air introduced into the room from the outside. Since bacteria are mainly attached to suspended particles, they can be effectively removed while filtering out particles.
Secondly, it is equally important to organize the air flow and discharge. By organizing a specific form and intensity of airflow in the room, clean air is used to continuously dilute and eliminate dust pollutants generated in the production environment, ensuring continuous cleanliness of indoor air.
Finally, the formation of indoor air static pressure is also a necessary measure. This helps to prevent polluted air from entering the room through the cracks of the door and other parts, further ensuring the cleanliness of the indoor air.
In addition to cleanliness requirements, the clean air entering the purification workshop also needs to meet temperature and humidity standards. Generally speaking, the temperature of the clean room is controlled between 18 and 28, and the relative humidity is kept in the range of 45% to 65%. At the same time, in order to ensure the physiological needs of personnel, the fresh air ratio of the clean room should not be less than 15%. However, in certain climatic conditions or in air purification systems with high exhaust air requirements, the fresh air ratio may need to be adjusted appropriately.
In the air purification system, starting with the inhalation of fresh air, it is usually divided into **filtration. The primary filter is used to remove dust particles larger than 10 m, the intermediate or sub-high efficiency filter is used to filter out dust particles of 1 10 m, and the high-efficiency filter mainly removes dust particles smaller than 1 m. In special cases, four-stage filtration may also be used, i.e., a high-efficiency filter is added after the first stage. Often, filters with different efficiencies are used together to meet different cleanliness requirements.
Next, we take a closer look at the functions of the various types of filters:
Primary filter: It mainly removes dust particles larger than 10 m, which is used for fresh air filtration and air conditioning unit protection. The filter material is WY-CP-200 polyester non-woven fabric, and the filter material can be washed and reused.
Intermediate filter: It mainly removes dust particles of 1 10 m, and is generally placed in front of the high-efficiency filter and behind the fan to protect the high-efficiency filter. The common one is a bag-type medium-efficiency filter, and the filter material is WZ-CP-2 polyester non-woven fabric.
Sub-high efficiency filter: It can filter out dust particles less than 5 m, and the filter material is generally glass fiber products. (Generally not selected).
High-efficiency filter: Mainly used to filter out dust particles less than 1 m, it is usually installed on the high-efficiency air supply outlet at the end of the ventilation system of the air purification system. The filter material is ultra-fine glass fiber paper, and the dust filtration efficiency is as high as 99More than 97%. High-efficiency filters are characterized by high efficiency but high resistance.
When choosing an air filter, the correct selection of the HEPA filter is a key factor to ensure that the cleanliness is up to standard. According to the latest research data, the penetration rate of high-efficiency filters against bacteria (organisms above 1 m) is only 00001% against viruses (0.organisms above 3 m) with a penetration rate of 00036%。This means that the HEPA filter removes almost 100% of bacteria, i.e. the air that passes through a qualified HEPA filter can be considered sterile.
The performance of air filters is evaluated based on four main indicators: air volume, filtration efficiency, air resistance and dust holding capacity.
Air volume: The air volume through the filter is equal to the filter section wind speed multiplied by the filter cross-sectional area multiplied by 3600 (units converted to cubic meters per hour).
Filtration efficiency: At the rated air volume, the difference between the dust concentration of the air before and after the filter and the percentage of the dust concentration in the air before the filter is called the filtration efficiency. In addition, the transmittance is also an indicator to visually evaluate the effectiveness of the filter, which indicates the percentage of the dust concentration in the air after the filter and the dust concentration in the air before the filter.
Resistance: The resistance encountered by air flowing through the filter is a component of the total resistance of the HVAC system. The resistance increases with the increase of filtration rate and is proportional to the dust holding capacity. The resistance of a new filter is called the initial resistance, while the resistance when the dust holding capacity reaches the specified maximum is called the final resistance. In general, the final resistance of medium and high efficiency filters is about 2 times the initial resistance.
Dust holding capacity: The amount of dust inside the filter when the final resistance is reached at the rated air volume.
Since dust particles often act as carriers of bacteria, it is critical to reduce microorganisms in the cleanroom and improve cleanliness. This requires minimizing eddy currents, avoiding contamination from outside the work area into the work area, preventing secondary dust flying, etc. In order to dilute the dust concentration in the air, it is necessary to ensure adequate ventilation and air change. At the same time, the airflow in the work area should be as uniform as possible and meet process and hygiene requirements to ensure that dust in the air can be effectively removed. It should be noted that the dust in the clean workshop is mainly due to personnel activities, accounting for about 80% to 90%, while the contribution of buildings and purified air supply systems is relatively small.