Air Conditioner Classification:
Comfortable air conditioner - take temperature as the main control object to meet people's comfort requirements;
Precision air conditioning - with temperature and relative humidity as the main control object, to meet the requirements of industrial production (constant temperature and humidity);
Clean (purifying) air conditioning - taking the number of air particles as the main control object to meet the requirements of industrial production (cleanliness).
What is a Cleanroom?
- Specially designed rooms should control the number of dust particles in the air, and the design should control the invasion, survival and retention of dust particles into the room to minimize, and the related temperature, humidity and pressure should be controlled as necessary. (Source: ISO14644-1)
- Specially designed and constructed confined spaces with special controls in terms of air particles, temperature and humidity, air pressure, air pressure flow patterns, air movement, vibration, noise, microbial growth, and lighting. (From: ASHRAE)
- By application:
Industrial clean room: the main control object - particles;
Biological clean room: the main control object - particles, microorganisms.
- According to the airflow flow type: unidirectional flow clean room, non-unidirectional flow clean room, mixed flow clean room.
Unidirectional flow cleanroom:
1) The airflow passes through the entire section of the clean area;
2) The wind speed of the section is uniform and stable;
3) The streamlines are single and roughly parallel;
4) Controlled airflow.
- Relying on the "piston" squeezing effect of the air supply airflow, the indoor dirty air is quickly discharged to the outdoors to achieve the purpose of purification.
—The full distribution rate of high-efficiency filter is >80%.
Non-unidirectional flow cleanroom:
1) Uneven airflow velocity;
2) the airflow has multiple directions (reflux, vortex);
3) controlled airflow;
- Rely on the supply air flow to continuously mix and dilute the indoor air, and gradually remove the indoor particles until the equilibrium is reached.
- Ensure sufficient air exchange times and reasonable airflow organization.
Mixed Flow Cleanroom:
1) Unidirectional flow and non-unidirectional flow exist at the same time;
2) The two airflows do not interfere with each other (independent);
3) Controlled airflow
—Localized one-way flow protection
—The background is a non-unidirectional flow state
GB50073-2013 "Code for Clean Plant Design" air cleanliness level requirements:
3.0.1 The air cleanliness level of suspended particles in the air in the clean room and clean area shall comply with the following requirements:
1. The integer level of air cleanliness in clean rooms and clean areas shall be determined according to Table 3.0.1.
Table 3.0.1 Integer levels of air cleanliness in clean rooms and clean areas
Note: Depending on the measurement method, the significant digits for concentration data at each grade level should not exceed 3 digits.
| EU WHO 中国 GMP Cleanliness level | Maximum permissible particulate concentration limit (pc/m3) | |||
| Static | dynamic | |||
| ≥0.5μm | ≥5.0μm | ≥0.5μm | ≥5.0μm | |
| Grade A | 3520 | 20 | 3520 | 20 |
| Class B | 3520 | 29 | 352000 | 2900 |
| Class C | 352000 | 2900 | 3520000 | 29000 |
| Class D | 3520000 | 29000 | No prescripts | No prescripts |
A dynamic standard for microbial monitoring in GMP clean areas
| level | Plankton cfu/m3 | Sedimentation bacteria cfu/4h | Surface microorganisms | |
| Contact discs CFU/Dish | 5-finger gloves cfu/gloves | |||
| A | <1 | <1 | <1 | <1 |
| B | 10 | 5 | 5 | 5 |
| C | 100 | 50 | 25 | |
| D | 200 | 100 | 50 |
Cleanroom control parameters
Suspended particulates and microorganisms – important parameters that affect product purity, cross-contamination and sterility, and achieve cleanliness levels;
Temperature and relative humidity – influencing product process conditions and bacterial reproduction conditions, as well as personnel comfort.
| 20~24℃ | 45~60%（A、B、C级） |
| 18~26℃ | 45~65% (Grade D and below) |
The number of air changes and the cross-section air velocity are important factors for cleanliness.
Cross-section wind speed – refers to the wind speed in the working area of the unidirectional flow.
Concept of the work area:
China – an area between 0.8 m and 1.5 m above the ground
United States – an area above 0.6 m above the ground and below 0.9 m from the ceiling
One-way flow wind speed (Class A, Class 100, Class ISO5)
国际标准 ISO14644-4—v=0.2~0.5m/s
洁净厂房设计规范GB50073-2013--v=0.2~0.4m/s
Design code for clean workshop in electronics industry GB50472-2008--v=0.2~0.45m/s
中国cGMP 2010版--v=0.36~0.54m/s
0.2m/s仍然是单向流的保证风速
Conventional Cleanroom:
"The one-way airflow system shall provide airflow at a uniform velocity (guideline) of (0.2~0.4m/s)* from the specified inspection position 15-30cm below the terminal filter or air distributor system."
*（0.2~0.4m/s 在此以GB50073规定值为例）
Differential Static Pressure – An important parameter for a cleanroom to maintain its internal pressure (static pressure).
Positive differential pressure: Prevent outside contamination of the cleanroom (most cleanrooms)
Negative differential pressure: prevents the outside world from being polluted by the cleanroom (cleanroom contaminated by certain dangerous microorganisms)
Differential Pressure—Refers to the pressure difference between the two sides of an adjacent room when the door is closed
Differential static pressure (Pa)
| region | Clean workshop design specifications | Design specifications for pharmaceutical clean workshops |
| Cleanroom to outdoor | ≥10 | ≥10 |
| Clean area: Unclean area | ≥5 | ≥10 |
| between different levels of cleanroom | ≥5 | ≥10 |
| Between cleanrooms of the same level* | — | ＞0** |
*: Refers to different functional areas (rooms) of the same cleanliness level
**: >0 refers to the appropriate differential pressure gradient or flow direction
Illuminance – the process and production conditions that affect the product:
The clean area is usually artificially lit, with a minimum illumination of not less than 150lx, and the main working area is usually 200~300lx;
The minimum illumination of the non-clean area shall not be less than 100lx, which shall be formulated according to the requirements of various industry specifications.
Noise – control noise, protect the health of personnel, and facilitate the normal operation of workers:
| Unidirectional flow cleanroom | ＜65dB(A) | Empty state |
| Mixed-flow cleanroom | ＜65dB(A) | Empty state |
| Non-unidirectional flow cleanroom | ＜60dB(A) | Empty state |
Purification air conditioners are designed to provide a cleanroom-compliant system that meets the requirements of the product and ensures that it meets the production environment of the product.
Main Differences Between Purifying Air Conditioner and General Air Conditioner (HVAC Design)
| General air conditioning | Purify air conditioners | |
| Air filtration | No or coarse (moderate) filtration | Coarse-efficiency, medium-efficiency (high-efficiency), high-efficiency three-stage (four-stage) filtration |
| Temperature and humidity control accuracy | There are no clear control requirements | Control accuracy: DB—±2°C RH— 5~10% |
| Fresh air volume | Meet personnel hygiene requirements | Process equipment exhaust, room positive pressure, personnel fresh air |
| Air Treatment | Maximum supply air temperature difference | Low temperature difference between supply air (reheating, humidification) |
| Supply air volume | There is no requirement for the number of air changes | There is a requirement for the number of air changes (≥15ACH) and the air volume is large |
| Room differential pressure requirements | There are no explicit requirements | Differential pressure requirements (positive differential pressure, negative differential pressure) |
Unidirectional flow cleanroom (ISO5 Class A) design:
1. Isolator and RABS
Active type - (open, closed): The process equipment comes with a one-way flow circulation system.
Isolator Units (RABS):
The process equipment is equipped with only a barrier system, and the HVAC professional organizes the circulating air.
2. AHU circulatory system
AHU treats all circulating air and controls the temperature and humidity in the area, and is generally used in small areas.
The air duct section and occupied space are large, and it is difficult to lay the air duct, so the AHU needs an air-conditioning room.
The biggest advantage is the low noise level in the room.
Cycles are achieved separately with AHU and FMU
AHU—Ensure the temperature and humidity requirements in the core area, and arrange it in the computer room;
FMU - to ensure the purification of the core area of the circulating air volume requirements, arranged in the ceiling;
It is used in large areas, especially in the whole room, ISO5 level;
3. AHU+FMU air self-circulation system
Cycles are achieved separately with AHU and FMU.
AHU—Ensure the temperature and humidity requirements in the core area, and arrange it in the computer room;
FMU - to ensure the purification of the core area of the circulating air volume requirements, arranged in the ceiling; It is used in large areas, especially in the whole room, ISO5 level;
4. AHU+FFU air purification unit circulation
It has the same features as the AHU+FMU described above.
AHU—Ensure the temperature and humidity requirements in the core area, and arrange it in the computer room;
FFU - to ensure the requirements of the purification circulating air volume in the core area, arranged in the ceiling; For smaller areas of ISO 5 or Class A;
5. FMU air self-circulation system
There are two ways to do this:
- With cold source: to ensure the temperature and humidity and circulating air volume requirements in the area;
- No cold source: only ensure the circulating air volume requirements.
The fan is arranged in the ceiling;
Non-unidirectional flow (turbulence) cleanroom design points:
1. Basic requirements for airflow organization
Function: Effectively organize the air supply and return air mode, give full play to the dilution effect of clean air, and quickly discharge indoor pollution.
Basic principle: The direction of the air flow should be adapted to the direction of natural sedimentation of particles, and the pollution should be discharged at the fastest speed.
Air supply outlet layout requirements:
1) Evenly arranged
2) Avoid the inlet and exhaust outlets of process equipment
3) Use the same specification HEPA
4) The arrangement of the air supply duct should be conducive to the balance of the airflow
Return air outlet layout requirements:
1) Try to arrange evenly on both sides
2) Avoid obstructions
3) The upper edge of the tuyere is ≤ 0.5 meters from the ground
4) Vertical louvers are adopted
5) Install filter (low resistance)
2. The basic requirements for air supply volume (number of air changes)
Dilution of room particles;
Eliminate indoor heat and humidity loads
the number of air changes recommended by the specification;
self-cleaning time requirements;
Effect of airflow organization:
**Diluted room particles:
The number of air changes is calculated from the known cleanliness and the simplified formula:
According to the required cleanliness level, room area, number of people in the room, indoor dust
quantity and fresh air ratio, etc., are calculated by specific formulas and charts.
**Elimination of indoor heat and humidity loads:
If the residual heat in the cleanroom is large, the supply air volume is calculated according to the maximum cooling load in summer:
If the residual humidity in the clean room is large, the air supply volume is calculated according to the maximum moisture dissipation capacity in the room:
**Self-cleaning time requirements; (15~20 minutes)
Self-cleaning time – the time it takes for a cleanroom to return from a contaminated state to its normal cleanliness state.
According to the parameters such as the pollution concentration before self-cleaning and the design concentration before the clean room, it is calculated by specific formulas and charts.
**Number of air changes
The Code for the Design of Clean Workshops recommends the following air changes (static)
| Cleanliness level | Number of air changes |
| ISO class | times/hour |
| 6 | 50~60 |
| 7 | 15~25 |
| 8~9 | 10~15 |
International Standard ISO14644-4 pairs of clean rooms for the microelectronics industry, recommended number of air changes (dynamic)
| Cleanliness level | Number of air changes |
| ISO class | times/hour |
| 6 | 70~160 |
| 7 | 30~70 |
| 8~9 | 10~20 |
**Effect of airflow organization
The layout of the air supply and return outlets directly affects the size of the air supply volume, and this factor should be fully considered in the design.
In conclusion: the final determined air supply volume or air exchange times should meet the requirements of the above five aspects at the same time. (i.e. the maximum value)
3. Differential pressure design
**Three Concepts:
Room differential pressure – resists external leakage (leakage) – ensures cleanliness
Relative differential pressure – to ensure the direction of air flow – to protect the product from contamination
Air lock – area isolation, "control" of differential pressure – protects the product (outside space) from contamination
Differential Pressure—Clean rooms create differential pressures to reduce contamination from unclean areas, outdoors, suspended ceilings, and similar areas.
Positive differential pressure: prevent contamination of the room from the outside world;
Negative pressure difference: prevent harmful air pollution from the outside world;
Relative Differential Pressure – The establishment of a relative differential pressure is primarily used to reduce the propagation of particles between exposed process operation protection, zones and areas not related to them, and to prevent contamination and cross-contamination.
**How to create a differential pressure:
Room positive pressure difference: air supply = exhaust air + leakage air (residual air volume is positive)
Negative pressure difference in the room: supply air + leakage air = exhaust air (residual air volume is negative)
Differential pressure calculation method: when the room door is closed, the air supply volume required for the room to maintain a certain differential pressure value is calculated:
Differential Pressure Method—Calculates the amount of leakage air.
L=0.827×A×∆P0.5×3600×1.25 m3/h
0.827 - air leakage coefficient, A - total area of the gap, ∆ P - pressure difference 1.25 - additional coefficient of imtightness.
The number of air changes method - estimating the leakage air volume, not recommended
For the clean area room, different pressure differences use different air exchange times: ΔP=5~40Pa, n=0.6~4.0 ACH
Air lock - a small chamber set up to block the air flow of the outside or adjacent chamber and ensure the pressure difference, generally set up at the entrance and exit of the clean area.
There are three types of air locks: The two doors of the air lock are interlocked, and only one door can be opened at all times, thus ensuring the pressure difference.
Used in critical areas.
Gradient airlock: The most commonly used form, the airflow flows from a high pressure through an airlock chamber to a low pressure.
It is used for isolation between different clean areas or between clean and non-clean areas.
Purpose: Protect the product; (Not polluted by the outside world)
Positive pressure air lock: The air lock chamber is located at the highest pressure, and the air flow flows out from the air lock chamber. It is used to separate the airflow between different areas.
Function: protect the product (from being polluted by the outside world), protect the outside world from being polluted, and prevent pollution from spilling out in the clean area; It is used for the isolation of strong drugs (high activity, high toxicity, high sensitization).
Negative pressure airlock: The airlock chamber is located at the lowest pressure, and the airflow flows from the outside to the airlock chamber. It is used to separate the airflow between different areas.
Function: It protects the product, protects other areas from pollution, and prevents the air overflow of products in the clean area; For example, it is used for the isolation of strong drugs (high activity, high toxicity, high sensitization).
Air conditioning load calculation: The calculation method is the same as that of ordinary air conditioners, please refer to the relevant design manual.
Air Conditioning Design:
Common basic schemes:
1. DC system
Fresh air for use in areas where recirculating air is not permitted; The enthalpy difference of the surface cooler of the air-conditioning equipment is large, and the number of rows is increased;
2. Primary return air system
A certain proportion of outdoor fresh air is mixed with indoor return air, which is suitable for most clean areas.
The system is simple and easy to control, and it is still the first choice at present.
The air supply parameters are adjusted by heating the coil.
It is the air treatment method recommended by GMP guidelines and international ISPE.
3. Secondary return air system
It is used in clean areas with high cleanliness and large air volume.
Since there is no cooling and reheating process of the return air, there is an energy-saving effect.
It is not suitable for areas with large moisture dissipation, such as liquid preparation and potting in the water needle workshop.
The means of adjusting the parameters are single, not easy to control, and are suitable for areas where the indoor heat source is relatively stable.
4. Special scheme - low humidity system
For use in areas with low relative humidity, a rotary dehumidifier + AHU is used.
Filter Classification:
The continental national standard divides air filters into two categories:
Air filters – coarse, medium, medium, high, and sub-high
Coarse efficiency: capture large particles ≥5 μm, and the efficiency is calculated as ≥2 μm particles;
Medium and high efficiency: capture medium particles ≥ 1 μm, and the efficiency is calculated as ≥0.5 μm particles;
Sub-high efficiency: Captures small particles ≥ 0.5 μm, and the efficiency is calculated as ≥ 0.5 μm particles.
Initial resistance of air filter:
粗效：25~50Pa（G1~G4）
中效：50~105Pa（M5、M6—原F5、F6）
高中效：100~140Pa（F7、F8）
亚高效：120~150Pa（F9、H10、H11）
高效：160~250Pa（H12~H14）
超高效:170Pa(U15~U17)
Resistance and efficiency index of air filter under rated air volume (from GB/T14295-2019)
High-efficiency air filters – high-efficiency, ultra-high-efficiency
Efficient: Captures small particles ≥ 0.5 μm, and the efficiency is calculated as ≥0.5 μm particles (sodium flame method)
Ultra-efficient: Captures ≥ 0.5μm particles, and the efficiency is calculated based on 0.1~0.3μm particles (scanning method)
初阻力：160~250Pa
HEPA filter efficiency requirements (from GB/T13554-2020)
Comparison of several air filter standards in major countries at home and abroad:
Filter usage:
Three-stage (or four-stage) air filter combinations are commonly used in the design of purified air conditioners:
Crude + Medium + High Efficiency (HEPA)
Crude Efficiency + Medium Efficiency + High Efficiency + High Efficiency (HEPA)
The higher the efficiency of air pre-filtration, the more effective the protection of the final HEPA filter.
Air Handling Unit Selection Points:
The inner wall material of the box is corrosion-resistant and easy to clean;
The air leakage rate of the unit <1%; Fan selection fan performance curve is steep;
dry steam humidifiers; micro-perforated plate muffler;
The blower is selected according to the total air volume and total resistance of the purified air conditioning system (the resistance of the pre-filter is selected by 1.5~2 times of the initial resistance).