The HVAC (purification air conditioning) system of pharmaceutical companies is one of the key systems to ensure the quality of drugs, and the pressure difference control is a key link in the purification of air conditioning systems by pharmaceutical companies. Only by ensuring reasonable airflow organization and effective control of differential pressure can the GMP-specified cleanliness requirements and process requirements be met.
Article 16 of the GMP stipulates that the windows of the clean room (area), the ceiling and the pipes, tuyères, lamps and walls or ceilings that enter the room shall be sealed. The static pressure difference between adjacent rooms with different air cleanliness levels should be >5Pa, and the static pressure difference between the clean room (zone) and the outdoor atmosphere should be >10Pa, and there should be a device indicating the pressure difference. In order to meet this requirement, pharmaceutical companies must set up HVAC systems.
The composition of the 1HVAC system
The task of the HVAC system is to ensure that the air parameters of the clean room reach the required state, usually consisting of ventilation system, air treatment equipment, cold source/heat source, air conditioning water system and automatic control system.
HVAC system construction
(1) Ventilation system: including air supply system, return air system and exhaust system.
(2) Air treatment equipment: The air is subjected to various treatments (purification, heating, cooling, humidification, dehumidification, etc.) by physical means to achieve a prescribed state.
(3) Cold and heat sources: The cold source is usually a refrigeration equipment such as various types of chillers, which provides 7~12 °C low temperature water for air treatment equipment; the heat source usually includes electric heaters, boilers, hot water and heat pump units, etc. The processing equipment provides heat.
(4) Air conditioning water system: including circulating water pump and its piping system.
(5) Automatic control system: including air purification, temperature and humidity control, differential pressure control, and automatic control and adjustment devices for safety and energy saving.
The basic process of 2HVAC system 2.1 The difference between HVAC system and general air conditioning system Due to the special processing technology and GMP requirements of pharmaceutical companies, the HVAC system process requirements also have its characteristics to ensure air cleanliness, temperature and humidity, pressure difference, air volume and wind speed in the production area. The technical requirements of microbes, etc., are different from those of general air conditioning systems mainly in air filtration, airflow organization, indoor pressure control, air volume energy consumption and cost.
2.2 Basic Process The outdoor atmosphere (fresh air) enters the air conditioning unit through the air supply duct, and is treated by the corresponding temperature and humidity, and is filtered and filtered by the primary and secondary effects. The air blower is sent to the air supply duct and distributed to each air supply port (with high efficiency filtration). The device enters the production area. The clean room is provided with a return air outlet or an exhaust air outlet. A part of the clean room air is returned to the air conditioning unit through the air return port, and the other part is discharged to the outside by the exhaust fan through the air exhaust port.
3 Clean room pressure difference control 3.1 The purpose of differential pressure control is to ensure that when the clean room is temporarily damaged or the air balance is temporarily damaged, the air flow can flow from the area with high air cleanliness to the area with low air cleanliness, so that the clean room is clean. It is not disturbed by polluted air, so the clean room must maintain a certain pressure difference.
3.2 Clean room pressure difference establishment principle and differential pressure air volume determination 3.2.1 Clean room pressure difference selection Clean room pressure difference should be selected appropriately, the selection is too small, the clean room pressure difference is easy to be destroyed, the cleanliness is disturbed; Too large, the HVAC system's new air volume increases, the load increases, and the filter life is shortened. Therefore, the clean room pressure difference should be reasonably determined. (For normal clean room, positive pressure, biological safety clean room is negative pressure)
The pressure difference of the clean room is maintained by the amount of fresh air sent into the air. That is, the basic principle of the pressure difference is that the air supply volume is greater than the sum of the return air volume, the exhaust air volume, and the air leakage volume. The air leakage amount depends on the building maintenance. The degree of sealing of the structure, such as door joints, window joints, wall joints, various pipeline interfaces and other gaps, will affect the amount of air leakage, making the indoor pressure difference difficult to maintain or unstable. Whether it is a fresh air system or a recirculating air system, the pressure difference is established by balancing the air volume of the clean room with the air volume and the air volume (remaining air volume).
3.2.2 Determination of the air pressure difference in the clean room For the determination of the air pressure difference of the clean room, the air exchange frequency method and the gap method are generally adopted. The gap method considers both the airtightness of the clean room enclosure structure and the maintenance of the indoor pressure difference. The amount of air required to control the value is therefore more reasonable and accurate than the number of times of ventilation.
According to the pressure difference maintained by the clean room, the required differential pressure air volume can be calculated as follows:
Q=a-Σ(q·L)
Where Q--the pressure difference air volume required to maintain the clean room pressure difference, m3/h;
A--The safety factor determined according to the airtightness of the envelope structure may be 1.1 to 1.2;
Q--When the clean room is a certain pressure difference, the leakage air volume per unit length of the envelope structure, m3/h·m;
L--the length of the gap of the envelope structure, m.
3.3 Clean room pressure difference 3.3.1 Fluctuating factors of clean room pressure difference Fluctuating factors affecting clean room pressure difference: usually including outdoor wind pressure and wind speed change; HVAC system resistance change; duct leakage and clean room maintenance structure Change in air tightness, etc.
3.3.2 Clean room pressure difference control method The clean room pressure difference control method is based on the principle of pressure difference establishment, and its influencing factors are effectively controlled or adjusted to maintain the stability of the clean room pressure difference. The clean room differential pressure control method is divided into human intervention adjustment and automatic control.
3.3.2.1 Human intervention to adjust the clean room pressure difference method (1) Regularly check and maintain the airtightness of the clean room envelope structure, minimize the amount of air leakage; clean or replace the filter regularly to ensure the normal resistance of the system.
(2) Return air outlet control: It is a simple and effective method. By changing the resistance of the louver grille or the air damping layer on the tuyere to adjust the return air volume, the purpose of the differential pressure control is achieved. Because the volume of the louver is not large, it will change the direction of the airflow, so this method can only be coarse adjustment.
(3) Residual pressure valve control: When there is enough residual air volume in the clean room, the balance pressure block on the residual pressure valve can be adjusted, and the opening degree can be changed to realize the differential pressure control.
(4) Adjust the return air damper or exhaust damper.
(5) Adjust the fresh air valve or air supply valve.
3.3.2.2 Automatic control of clean room pressure difference method (1) Sensor control: through the corresponding sensor to detect indoor pressure difference or send or exhaust line pressure or wind flow, and then adjust the air supply volume or exhaust air volume, you can pass the pipeline The speed of the electric valve or fan (inverter control fan) is realized, which is a more accurate automatic control, which is currently used more.
(2) Microcomputer control system: including direct digital control system and distributed control system. They are based on microprocessor and realize automatic monitoring. They can better ensure the technical requirements while ensuring the safe operation of the system and various indicators. Zui achieves energy-saving control to a large extent. The microcomputer control system directly inputs the output signal of the sensor or the transmitter in the system to the microcomputer, and directly drives the actuator (electric sealing valve, etc.) after being processed by the microcomputer to realize the clean room pressure difference, temperature and humidity, and cleanliness. Detection, control and management of indicators.
4 Conclusion The implementation of the new version of GMP, which draws on international advanced standards and drug regulatory experience, pays more attention to science, which focuses on refining the software requirements, and also puts forward higher technical requirements in hardware, especially the key clean design principles. The changes, pressure difference and cleanliness level will bring about an increase in energy consumption. Reasonable layout, reduced cross-contamination and low energy consumption are the key to transformation. Pharmaceutical companies face greater opportunities and challenges. Computer control and network technology are bound to be widely used in HVAC system operation and maintenance management.
