Replacement Of HEPA Filter

The HEPA filter should be replaced in any of the following cases:
Table 10-6 Clean air monitoring frequency of clean room

1. The airflow speed is reduced to a minimum. Even after replacing the primary and medium air filters, the airflow rate cannot be increased.
2. The resistance of the HEPA air filter reaches 1.5 times to 2 times the initial resistance.
3. The HEPA air filter has an unrepairable leak.

6. Comprehensive performance test after end filter replacementAfter cleaning the heat and humidity treatment equipment and the fan in the air conditioning system, the system fan should be started to put the purification system into operation, and the comprehensive performance test is carried out. The main contents of the test are:
1) Determination of system delivery, return air volume, fresh air volume, and exhaust air volume
The system sends, returns air volume, fresh air volume, and exhaust air volume are measured at the air inlet of the fan or at the air volume measuring hole on the air duct, and the relevant adjustment mechanism is adjusted.
The instrumentation used in the measurement is generally: a sub-management and micro-pressure gauge or an impeller anemometer, a hot ball anemometer, and the like.

2) Determination of airflow velocity and uniformity in clean room
The unidirectional flow clean room and the vertical unidirectional flow clean room are measured at 10 cm below the high-efficiency filter (30 cm in the US standard) and on the horizontal plane of the working area 80 cm from the floor. The distance between the measuring points is ≥2 m, and the number of measuring points is not less than 10.
The airflow speed in the non-unidirectional flow clean room (ie, the turbulent clean room) is generally measured at a wind speed of 10 cm below the air supply port. The number of measuring points can be appropriately arranged according to the size of the air supply port (generally 1 to 5 measuring points).

6. Comprehensive performance test after end filter replacementAfter cleaning the heat and humidity treatment equipment and the fan in the air conditioning system, the system fan should be started to put the purification system into operation, and the comprehensive performance test is carried out. The main contents of the test are:
1) Determination of system delivery, return air volume, fresh air volume, and exhaust air volume
The system sends, returns air volume, fresh air volume, and exhaust air volume are measured at the air inlet of the fan or at the air volume measuring hole on the air duct, and the relevant adjustment mechanism is adjusted.
The instrumentation used in the measurement is generally: a sub-management and micro-pressure gauge or an impeller anemometer, a hot ball anemometer, and the like.

2) Determination of airflow velocity and uniformity in clean room
The unidirectional flow clean room and the vertical unidirectional flow clean room are measured at 10 cm below the high-efficiency filter (30 cm in the US standard) and on the horizontal plane of the working area 80 cm from the floor. The distance between the measuring points is ≥2 m, and the number of measuring points is not less than 10.
The airflow speed in the non-unidirectional flow clean room (ie, the turbulent clean room) is generally measured at a wind speed of 10 cm below the air supply port. The number of measuring points can be appropriately arranged according to the size of the air supply port (generally 1 to 5 measuring points).

3) Detection of indoor air temperature and relative humidity
(1) Before the indoor air temperature and relative humidity are measured, the purified air-conditioning system should have been continuously operated for at least 24 hours. For places with constant temperature requirements, the measurement should be continuous for more than 8 hours according to the requirements of temperature and relative humidity fluctuation range. Each measurement interval is not more than 30min.
(2) According to the fluctuation range of temperature and relative humidity, the corresponding instrument with sufficient accuracy should be selected for measurement.(3) Indoor measuring points are generally arranged in the following places:
a. send, return air outlet
b. Representative locations in the constant temperature working area
c. room center
d. sensitive components

All measuring points should be at the same height, 0.8m from the floor, or according to the size of the constant temperature zone, respectively, arranged on several planes at different heights from the ground. The measuring point should be greater than 0.5m from the outer surface.
4) Detection of indoor airflow patterns
For the detection of indoor airflow patterns, it is actually a key issue to check whether the airflow organization in the clean room can meet the cleanliness of the clean room. If the airflow pattern in the clean room cannot meet the requirements of airflow organization, the cleanliness in the clean room is also It will not or is difficult to meet the requirements.
Clean indoor airflow is generally in the form of a top-down. The following two issues need to be resolved during detection:
(1) Measuring point arrangement method
(2) Observe and record the flow direction of the airflow point by point using the cigarette lighter or the hanging monofilament thread, and mark the airflow direction on the sectional view with the measuring points arranged.
(3) Comparing the measurement record with the last measurement record, and finding that there is a phenomenon that is inconsistent or contradicts the indoor airflow organization, the cause should be analyzed and processed.

5) Detection of streamline misuse (for the detection of parallelism of streamlines in a unidirectional flow clean room)
(1) A single line can be used to observe the airflow direction of the air supply plane. Generally, each filter corresponds to one observation point.
(2) The angle measuring device measures the angle of the airflow away from the specified direction: the purpose of the test is to verify the parallelism of the airflow throughout the working area and the diffusion performance of the interior of the clean room. Equipment used; equal power smoke generators, plumb or level, tape measure, indicator and frame.

6) Determination and control of indoor static pressure
7) Inspection of indoor cleanliness
8) Detection of indoor planktonic bacteria and sedimentation bacteria
9) Detection of indoor noise

1. Air filter replacement cycle
The air filters of each level used in the purification air conditioning system should be replaced under what circumstances, according to their specific conditions.
1) Replacement of fresh air filter (also known as pre-filter or initial filter, coarse filter) and intermediate air filter (also known as medium air filter), which can be twice the initial resistance of air resistance Time to proceed.
2) Replacement of the end air filter (generally a sub-efficient, efficient, ultra-efficient air filter).
The national standard GBJ73-84 stipulates that the airflow speed is reduced to a minimum. Even after replacing the primary and medium filter, the airflow speed cannot be increased; the resistance of the HEPA air filter reaches twice the initial resistance; The filter should be replaced if there is an unrepairable leak.

2. The choice of air filter
After purging the air conditioner for a period of time, the air filter used in the system must be replaced. The following points should be noted for the replacement of the filter:
1) First, use an air filter that is consistent with the original filter model, specifications, and performance (even the manufacturer).
2) When adopting new models and specifications of air filters, the installation possibility of the original installation frame should be considered, and should also be considered.

3. Air filter removal and purification air conditioning system delivery, return air line cleaning
For the purification air conditioning system before the removal of the original air filter (mainly referred to as the end of the efficient or ultra-efficient air filter), the equipment in the clean room should be wrapped and covered with a plastic film to prevent the air filter at the end. After the dismantling and dismantling, the dust accumulated in the air duct, static pressure box, etc. falls, causing pollution to the equipment and the floor.
After the air filter in the system is removed, the installation frame, air conditioner, delivery, and return air ducts should be carefully and thoroughly cleaned.
When removing the air filter in the system, it is recommended to follow the order of the primary (new air) filter, the medium efficiency filter, the sub-high efficiency filter, the high efficiency filter and the ultra-efficient air filter, which can reduce the dust entering the clean room. the amount.
Since it is not easy to replace the air filter at the end of the air conditioning system and the replacement cycle is long, it is recommended to perform an overhaul of all the equipment in the system while replacing the end air filter.

4. Remove fine dust particles
After the air filter in the system is removed and completely removed, the fan in the system can be started to blow off all the air ducts, mainly the air supply duct) and the end filter installation frame and the clean room, so as to adhere to the relevant surfaces. Fine dust particles have their fire resistance properties.

5. The end (sub-efficient, efficient, ultra-efficient) air filter replacement
In the purification air conditioning system, the installation of the air filters at all levels, which plays a key role in ensuring the cleanliness of the clean room, is the end filter.
End filters in cleanrooms generally use high-efficiency, ultra-efficient filtration or low-permeability filters, which have very high dust filtration efficiency and therefore have the disadvantage of being easily clogged. Generally, in the operation of the clean room, it is often inconvenient to remove and replace the terminal filter in the main air supply duct in the clean room and the clean air conditioning system due to the relationship between the indoor work and the cleanliness of the clean room. The upper side of the device is designed to reduce the particle concentration to the concentration required for the cleanliness of the clean room, and to extend the life of the end filter, an intermediate filter is placed in front of the high efficiency or ultra high efficiency filter.