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In cleanrooms and special environments, air quality is critical, especially in some demanding industries such as pharmaceuticals, food, and Electronic manufacturing. In order to keep the indoor air clean, the efficiency of air filters and air purification systems plays a decisive role. So, how long does it take for an air filter to clean a room? In this article, we will explore this issue in depth and analyze the difference between self-cleaning time and recovery time in detail for you, and how they affect the recovery of air quality.
What is self-cleaning time and recovery time?
Self-cleaning time refers to the time required for the air filtration system to reduce the concentration of particles in the air to a predetermined standard after the personnel in the cleanroom leave. In simple terms, it is the process of the filtration system recovering from a "dynamic state" to a "static state". The recovery time refers to the time required for the system to restore the concentration of particles in the air to the initial set standard after the modular cleanroom has increased due to some reasons (such as personnel entering or equipment starting). Although these two times seem similar, they are actually two different tests, and have different requirements for the air purification effect of the cleanroom.
1. Self-cleaning time
Self-cleaning time is usually the time it takes for the filtration system to restore the dust concentration in the room to the static standard after the personnel or pollution source exits. The standard stipulates that this process should generally be completed within 15-20 minutes. The length of the self-cleaning time is closely related to the air flow rate, air exchange rate and performance of the air conditioning purification system in the room.
2. Recovery time
Recovery time refers to how long it takes for the filtration system to restore the particle concentration to a qualified level after the particle concentration in the clean room is contaminated. According to the ISO 14644-3 standard, the recovery time should ensure that the particle concentration can be reduced to within 1% of the initial value within the set time. The recovery time is generally long, usually more than 30 minutes, depending on the air flow in the room and the efficiency of the filtration system.
3. Dynamic and static state
In these tests, "dynamic state" refers to an environment with active pollution sources, while "static state" refers to a state without pollution sources and a stable environment. The tests of self-cleaning time and recovery time are based on the process of transitioning from dynamic state to static state.
How to measure self-cleaning time?
The measurement of self-purification time is not done randomly, it needs to follow strict test standards. When testing the self-purification time, first of all, it is necessary to ensure that the air filtration system in the clean room is running stably. According to the provisions of GB 50591-2010 and ISO 14644-3, a dust particle counter is required to measure the particle concentration during the test.
1. Dust particle counter use
Dust particle counter is a standard device for measuring the concentration of particles in the air. Through this device, we can accurately record the changes in particle concentration at different time points in the clean room, and then calculate the time required for self-purification.
2. Test standards and methods
According to relevant standards, the test is usually carried out when the indoor dust concentration is close to the atmospheric dust concentration. In other words, before the test, it must be ensured that the indoor pollutant concentration is at a normal level and the air conditioning purification system is in a stable operating state. The goal of the test is to reduce the particle concentration in the room to the static particle limit within 15-20 minutes.
3. Aerosol initial concentration
At the beginning of the test, the indoor aerosol initial concentration needs to be recorded and compared with the standard particle concentration. Subsequently, the changes in the concentration of particulate matter during the operation of the air purification system were recorded, and the time required from "dynamic" to "static" was finally calculated.
Factors affecting self-purification time
The length of self-purification time depends not only on the performance of the air purification system, but also on many factors such as the design of the clean room, the air flow method, and the operating conditions.
1. Air circulation and ventilation frequency
Air circulation and ventilation frequency in the clean room are one of the main factors affecting the self-purification time. According to the ISO 14644 standard, the air exchange rate should be more than 3 times/hour to ensure that the air can circulate effectively and remove particulate matter. A higher air exchange rate can reduce the concentration of pollutants in the room more quickly and shorten the self-purification time.
2. Efficiency of the filtration system
The air filtration system of the clean room must have efficient filtration capabilities. Usually, HEPA (high-efficiency particulate air) filters are used to filter fine particles in the air, and the filtration efficiency can reach more than 99.97%. This efficient filtration capacity is the key to shortening the self-purification time.
3. Cleanroom design and size
The area and airflow design of the cleanroom will also affect the length of the self-cleaning time. Smaller rooms may achieve shorter self-cleaning times due to faster air flow; while larger rooms may take longer to reach the same particle concentration.
Self-cleaning time in actual applications
In actual applications, the self-cleaning time of a modular cleanroom is not just a theoretical calculation value, but also needs to be tested in combination with actual operations. Taking the pharmaceutical industry as an example, different degrees of pollutant release may occur during the production process, so the self-cleaning time test is particularly important.
1. Simulated operating state
When testing the self-cleaning time, an aerosol generator can be used to simulate the particle release in actual operation. By artificially increasing the particle load in the room, the time required for the air purification system to remove pollutants to a qualified level is tested.
2. Simulated dynamic load
For example, in a Class c CleanRoom, an aerosol generator can produce 0.5 micron particles to simulate the highest pollution load. Measure the time required for the air purification system to reduce the particle concentration to the static limit. Usually this process should be completed within 15-20 minutes.
3. Actual requirements of the industry
For most pharmaceutical and electronic industries, the self-cleaning time of clean rooms is strictly required. Industry specifications such as GMP (Good Manufacturing Practice for Pharmaceuticals) recommend that the self-cleaning time should be kept within 20 minutes to ensure that the air quality during operation can be effectively controlled.
Industry-related standards and specifications
In the testing of clean rooms and air filtration systems, following relevant standards and specifications is the basis for ensuring system performance and air quality. The following are several key standards and specifications:
GB 50591-2010:Clean room construction and acceptance specifications, which provides guidelines for the construction and verification of clean rooms, covering aspects such as air purification, equipment selection and testing methods.
ISO 14644-3:Test methods for clean rooms and related controlled environments, which specifies the air quality, particle measurement methods, air exchange rates, etc. of clean rooms in detail.
iso 14644-1:Clean Room Classification standard, which defines different levels of clean rooms and specifies the maximum allowable particle concentrations for each level of clean rooms.
EU GMP Annex 1:This is a standard for the design and operation of clean rooms in the pharmaceutical industry, which specifies the requirements for self-cleaning time and recovery time, especially the control standards for particle concentration.
How long it takes for an air filter to clean a room depends on many factors, such as air exchange rate, efficiency of the filtration system, Clean room design, etc. Under ideal conditions, the self-cleaning time of a clean room should be controlled within 15-20 minutes. By strictly following relevant industry standards and specifications and combining actual test data, it can ensure that the air quality in the clean room meets the requirements and provide effective protection for a high-demand production environment. In actual operation, reasonable air purification and testing methods are essential to maintaining the stability of the clean room environment.
