The purpose of the self-cleaning performance test is to determine the ability and rate of the cleanroom or clean facility to remove suspended particulate pollutants, which is the most important performance reflection of the non-unidirectional flow cleanroom.
The self-purification performance is expressed by the self-purification time of 100:1. ISO 14644 defines the 100:1 self-purification time as the time required for the particle concentration to drop to 0.01 times the initial concentration.
Internationally, the number of air changes in a room is an important parameter of an air conditioning system.
ISO14644, NEBB's Procedural Standards for Clean Room Certification Test and GB 50073 Code for Design of Clean Workshops all recommend regular testing of the clean room self-cleaning time.In this paper, based on the calculation based on the uniform distribution theory, discussing the relationship between the self-cleaning time and the number of air changes.
|
number of air changes(t/h) |
self-cleaning time(min) |
|
10 |
27.6 |
|
15 |
18.4 |
|
20 |
13.8 |
|
25 |
11.0 |
|
30 |
9.2 |
|
35 |
7.9 |
|
40 |
6.9 |
|
45 |
6.1 |
The self-cleaning time measured during the actual test may differ slightly from the theoretical arithmetic results, because the theoretical calculation formula is based on the uniform distribution theory, and the airflow organization of the actual clean room cannot achieve the uniform distribution of indoor particles.
The particle distribution in a cleanroom may have a model consisting of 4 unevenly distributed areas: the main flow area, the vortex area, the return air outlet area and the dust production area.
In the dust production area, the particulate matter has a certain initial momentum, and its diffusion is mainly affected by the initial momentum, and when its momentum decays to a certain extent, the particulate matter diffuses with the indoor airflow.
Part of it mixes into the vortex area, while the other part enters the main flow area; Part of the particulate matter in the main flow area folds back to the vortex area with the return flow, distributes in the vortex area and leads the air flow back to the main flow area with the main flow area, so that the particulate matter circulates indoors again and again and has a long retention time.
For this reason, the actual self-cleaning time may be greater than the theoretical self-cleaning time. In order to minimize the effect of unevenness, multiple measurement points can be set during the measurement, and then the average of each point can be taken.
Cleanroom ventilation frequency standard reference
1. In the cleanroom standards of various countries, the number of air changes in the same level of non-unidirectional flow cleanroom is not the same.
China's Code for the Design of Clean Plants (GB 50073-2001) clearly stipulates the number of empirical air changes required for the calculation of clean air volume in different levels of non-unidirectional flow clean rooms.In addition, the international standard for laboratory animal environment and facilities GB14925-2001 stipulates that the ordinary environment is 8~10 times/h; Barrier environment 10~20; isolation environment 20~50.
2. Temperature and relative humidity
The temperature and relative humidity of the clean room (zone) should be adapted to the pharmaceutical production process.When there are no special requirements, the temperature should be controlled at 18~26 °C, and the relative temperature should be controlled at 45%~65%.
3. Pressure difference
(1) The clean room must maintain a certain positive pressure, which can be achieved by making the air supply volume greater than the exhaust air volume, and there should be a device indicating the pressure difference.(2) The static pressure difference between adjacent rooms with different air cleanliness levels should be greater than 5Pa, and the static pressure difference between the clean room (area) and the outdoor atmosphere should be greater than 10Pa, and there should be a device indicating the pressure difference.
(3) The process produces a large amount of dust, harmful substances, explosive substances and the production of penicillin strong allergenic drugs, certain steroid drugs, any microorganisms considered to have pathogenic effects, the operation room and its adjacent rooms or areas should maintain a relative negative pressure.
4. Amount of fresh air
A certain amount of fresh air should be maintained in the clean room, and its value should be the maximum of the following air volumes:(1) 10%~30% of the total air supply volume of the non-unidirectional flow clean room, and 2%~4% of the total air supply volume of the unidirectional flow clean room.
(2) Compensate for the amount of fresh air required for indoor exhaust air and maintaining positive pressure value.
(3) Ensure that the fresh air volume per person per hour in the room is not less than 40m³.