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Calculation of air supply volume in clean room
Clean room air supply calculation
The calculation of the air supply volume in the clean room mainly refers to the calculation of the air volume under the conditions of known cleanliness or allowing the bacteria to be concentrated. The steps are as follows:
First, positive pressure clean room air supply Q I calculation
1 . Calculation of air supply volume in turbulent clean room Q1-1
The turbulent clean room - 1000 , 10000 , 100000 , 300000 clean room, the air supply is calculated based on the number of air changes:
Q I -1=KV
Where: K - the number of air changes;
V——the clean room volume;
N—— non-unidirectional flow clean room stable dust concentration;
G——the amount of dust generated per unit volume in the clean room;
M——Dust concentration of outdoor air;
S—— the ratio of the return air volume to the air supply volume;
ηH - the total efficiency of the filter on the return air path;
ηX - the total efficiency of the filter on the fresh air path.
In the actual engineering calculation, the number of ventilation times K is difficult to calculate by the above formula, and the number of experience ventilations is generally used. In the clean room standards of various countries, the number of experience ventilations of the same level of non-unidirectional flow clean room is not the same. China's "Code for Design of Clean Plants" ( GB 50073-2001 ) clearly specifies the number of experienced air exchanges required for the calculation of clean air supply for non-unidirectional flow clean rooms of different levels, as shown in the following table:
　
Air cleanliness level
GB 50073-2001
ISO/DIS 14644-4
Medical clean room design specification
Level 6 ( 1000 )
50 to 60
25 to 56
Level 7 ( 10000 level)
15 to 25
11 to 25
≥25
Level 8 ( 100000 level)
10 to 15
3.5 to 7
≥15
Level 9 ( 1000000 level)
10 to 15
3.5 to 7
≥12
Note: 1 The number of air changes is suitable for clean rooms with a floor height less than 4.0m .
2 If the number of people in the room is small and the heat source is small, the lower limit should be adopted.
3 The number of air changes in the clean room of more than 100000 is not less than 12 times.
Second, the system air supply Q II calculation
The air supply volume of the system should be based on the air supply volume of the clean room plus the air leakage of the system. For air duct systems and air conditioning equipment manufactured and installed in strict accordance with the "Cleanroom Construction and Acceptance Specifications", it is recommended that the air leakage rate be as follows:
　
Cleanliness level
Air leakage rate ( % )
system
Air conditioning equipment
Total εΣ
Lower than 1000
Level 1000 to below level 100
Equal to or above level 100
4
2
1
2
1
1
4
2
2
Where: ΣQ I is the sum of the air volume of each clean room.
Third, the system fresh air volume Q III calculation
1 . New air volume required to meet the hygiene requirements of the clean room Q1
( 1 ) For the general situation where there is no obvious harmful gas in the room, the fresh air volume per person per hour shall not be less than 40m3 according to the "Code for Design of Clean Plants" : Q1-1 = number of people × 40 m3 / h .
( 2 ) For the occurrence of multiple harmful gases in the room:
Q1-2= Qa + Qb + ... + Qn
Qa= La/Ta Qb= Lb/Tb ... Qn= Ln/Tn
Where: Qa...Qn - the amount of ventilation necessary to dilute various harmful gases;
La...Ln - the amount of each harmful gas;
Ta...Tn - each harmful gas allows high concentration of zui
Harmful gas allows high concentration of zui ( mg/ m3 )
　
Name
Allowable concentration
Name
Allowable concentration
Name
Allowable concentration
Carbon monoxide
acetone
Ethyl ketone
benzene
Toluene
30
400
50
40
100
Xylene
Methanol
Ethanol
Cyclic ethanol
Sulfur dioxide
100
50
1500
50
15
Trichloroethylene
Carbon tetrachloride
hydrochloric acid
gasoline
Ether
Hydroxide and nitric acid
30
25
15
350
500
5
Compare Q1-1 and Q1-2 , take the large amount of Zui for the new air volume required for health
2 . The amount of fresh air required to maintain positive pressure in the room Q2
( 1 ) Local exhaust air volume = Q2-1 ;
( 2 ) The air volume passing through the residual pressure valve = Q2-2 can be found in the specification of the residual pressure valve;
( 3 ) The amount of air leakage from the gap = Q2-3
Where: F1 - gap area;
E1 - the flow coefficient is usually taken from 0.3 to 0.5
V1 - leakage wind speed
ΔP—— Indoor and external pressure difference
Ï——The air gravity density is usually 1.2kg/m3 .
The above calculation of the gap method is cumbersome, and can also be calculated by another method of gas exchange times. The number of air changes is estimated based on the empirical value, that is, when the pressure difference of the clean room is 5 Pa , the number of air changes corresponding to the air volume is 1 ～ 2h - 1 , when the pressure difference of the clean room is 10Pa , the corresponding air exchange frequency is 2 ~ 4h - 1 . Because the air volume of the clean room is related to the air tightness of the clean room maintenance structure and the pressure difference maintained, when the number of air changes is selected, the upper limit can be taken for the airtight room, and the airtight room is good. The lower limit can be taken.
In summary, keep the positive air volume in the room:
Q2= Q2-1 + Q2-2 + Q2-3
When the requirements for the positive pressure chamber are particularly strict, the amount of air leakage from the switch door and the transfer window should also be added to Q2 .
3 . Meet a certain proportion of fresh air volume Q3
When the number of personnel or leaks cannot be known exactly, or as an estimate in the preliminary plan, a new proportion of the total air volume attributable to fresh air may be used to determine the fresh air volume.
According to the "Clean Plant Design Code", for the turbulent clean room, the fresh air volume should not be less than 10% to 30% of the total air volume . For the unidirectional flow clean room, the fresh air volume should not be 2% to 4 % of the total air supply volume. % . The principle is: the lower the cleanliness, the higher the fresh air ratio.
Of course, for all occasions where circulating air is used, or when the process requires or allows, the fresh air ratio may not be taken in the above ratio.
4 . Supplement the fresh air volume required for leakage of the air supply system Q4
Q4= System air supply volume × εΣ
=Q II ×εΣ
5 . System fresh air volume Q III
Compare ΣQ1 , ΣQ2, and ΣQ3 , take the large value of zui , and “Σ†is the sum of the air volumes of each room. Then add the system air leakage Q4 , which is the new air volume required after the system's zui.
Q III = ( ΣQ1 , ΣQ2 , ΣQ3 ) max + Q4
Fourth, the system's return air (circulating wind) quantity Q IV calculation
The circulating air volume of the system should be the total air supply volume of the system minus the fresh air volume. which is:
Q IV = Q II - Q III
Clean room cleaning operation process clean room test guidelines