According to technical inspection reports, over 30% of microbiological test results are denatured or show false negative/positive results due to substandard air convection control. Pressure gradient breakdown between functional rooms is the leading cause of mold spore contamination.

HVAC system design requires precise calculation of supply airflow, air exchange rate, and pressure gradient model. This is a core problem in maintaining an absolutely sterile environment for the microbiological culture area.

This article provides a comprehensive solution adhering to HVAC design standards and international regulations. We will explore the method of controlling pressure gradients along with cleanroom equipment from Duc Duong.

1. HVAC Aerodynamic Parameters

1.1 Air Exchange Rate and Forward Air Velocity

Central air conditioning (AHU) systems operate on a forced air exchange mechanism to remove suspended particulate matter. According to WHO Technical Report Series, No. 961 – Annex 5, the air exchange rate (ACH) must be maintained between 20 and 40 times/hour for Grade C and Grade B spaces.
For Grade A localized sterile areas, the forward air velocity must be controlled within the range of 0.36 m/s to 0.54 m/s. Compliance with GMP cleanroom standards helps create GMP-standard cleanliness levels, completely protecting agar plates from the risk of bacterial contamination.

GMP Cleanliness Level	Air Exchange Rate (ACH)	Progressive Airflow Velocity
Grade A	Unidirectional progressive airflow	0.36 – 0.54 m/s
Grade B	40 – 60 times/hour	Grade A floor space
Grade C	20 – 40 times/hour	Convection airflow through AHU
Grade D	10 – 20 times/hour	Convection airflow through AHU

1.2 Control of Internal Temperature and Humidity Parameters

Microbiological testing environments require absolute temperature and humidity stability to prevent denaturation of the culture medium. The HVAC system must continuously control the temperature at 22°C ± 2°C and relative humidity at 50% ± 5% RH.

If humidity exceeds 60% RH, mold spores will proliferate extremely rapidly. Conversely, excessively low humidity causes surface electrostatic phenomena, attracting microscopic dust particles to adhere to glassware.

2. Pressure Differential Standards

2.1 Positive Slope Pressure Differential Diagram

To prevent the intrusion of microorganisms from the outside, the testing area must apply the principle of positive slope pressure differential. The standard pressure differential value is maintained from +10 Pa to +15 Pa between adjacent cleanrooms, decreasing gradually from the microbial core outwards.
According to the plan, the Microbiology Room maintains the highest pressure (+30 Pa), progressing to the Environment Preparation Room (+20 Pa), the Dressing Room (+10 Pa), and finally reaching 0 Pa in the warehouse corridor. This sloping pressure model forces the airflow to always blow outwards when the door is opened, eliminating the risk of cross-contamination.

2.2 Arrangement of Air Return and Exhaust Systems Near the Floor

Aerodynamic principles stipulate that supply air vents must be located on the ceiling panel and return air vents placed near the base of the wall. The distance from the bottom edge of the return air vent to the factory floor is controlled from 0.1 m to 0.2 m.

The airflow will move progressively from top to bottom, drawing all fine dust particles into the return duct. This flow structure prevents air turbulence, helping the lab maintain optimal GMP cleanliness levels.

3. Integration of Grade A Sterilization Equipment

3.1 Configuration of HEPA H14 Filter Dust Mats in LK Lab Cabinets

To establish a localized Grade A ultra-clean culture zone without the cost of building a large cleanroom, Duc Duong distributes the LM-1800V Microbiological Culture Cabinet. The product uses synchronized technical data from the manufacturer LK Lab Korea.
The device utilizes HEPA H14 filters capable of mechanically separating >= 99.995% of particulate matter with a size of 0.3 µm. The vertical, reciprocating airflow creates an absolutely sterile Class 100 environment, completely isolating the culture samples from infectious agents.

3.2 Positioning the culture cabinet to avoid disrupting AHU airflow

The microbiological culture cabinet must be positioned close to the wall, avoiding direct placement under the ceiling air vents of the AHU system. The standard installation distance helps prevent conflicts between the cabinet’s reciprocating airflow and the room’s convective airflow.

In addition, the integrated short-wavelength 253.7 nm UV lamp sterilizes the work chamber before each shift. This combination ensures the air in the culture chamber remains absolutely sterile.
To receive 3D perspective drawings of the microbiological cleanroom HVAC system and a GMP-standard AHU airflow calculation manual, please click on the Contact Form to contact Duc Duong Company for detailed support from our project engineering team.

4. Interior planning to prevent pressure drop

4.1 Arranging laboratory workbenches at an 82-degree angle to eliminate dead corners

The placement of corner furniture directly affects airflow circulation. Duc Duong proposes installing the 82-inch corner laboratory workbench, fitted snugly to the corner wall structure.

The corner design completely eliminates the space behind the workbench – where liquids and suspended microorganisms often accumulate. The work surface is made from smooth, flat Phenolic Compact sheet, resistant to cleaning chemicals and preventing mechanical adhesion. This allows technicians to easily clean and disinfect with 70% alcohol.

The corner laboratory bench distributed by Duc Duong is an essential piece of equipment to support HVAC system design

4.2 Setting Up Dedicated Washbasins to Isolate Moisture Sources

Local humidity from instrument washbasins can distort the air humidity controlled by the AHU. We place dedicated laboratory washbasins from Duc Duong in a separate washing area adjacent to the inoculation room.
The product is made from a single piece of chemical-resistant PP plastic, with an integrated P-trap odor trap drainage system. This mechanical structure prevents microorganisms from growing back from the drain into the cleanroom air.

5. Preventing Pressure Gap Breaks

5.1 Causes of Pressure Drops from Airlock Interlocks

Cleanroom pressure drops often occur due to the simultaneous opening of two airlock doors. When the air barrier is broken, contaminated air from the corridor immediately rushes into the inoculation room.
In addition, the aging of the door sealing rubber gasket can also cause air leaks, leading to pressure gap breaks. This pressure drop creates conditions for microorganisms to invade, compromising the four established GMP-certified cleanliness levels in the factory.

5.2 Installation of VAV/CAV Control Valves and Magnehelic Sensors

To automatically control differential pressure, we install variable flow (VAV) or fixed flow (CAV) control valves on the HVAC ductwork. The system integrates a Magnehelic differential pressure gauge that visually displays the room pressure.
Airlock doors are equipped with electromechanical interlocks, preventing both doors from opening simultaneously. An audible alarm will automatically activate when the room pressure drops below +10 Pa.

6. HVAC System Validation Schedule

6.1 Frequency of HEPA Filter Leakage Measurements

Air handling systems need to be re-validated periodically to ensure integrity. According to TCVN 8664-3:2011 (ISO 14644-3:2005), HEPA filter leakage measurements (PAO/DOP test) and particulate matter classification must be performed every 6 to 12 months.

In addition, M&E engineers need to measure cleanroom recovery time (Cleanroom recovery test). The standard stipulates that the AHU must automatically remove dust, returning the room from an operating state to a resting state within 15 to 20 minutes.

6.2 Digitizing Environmental Parameter Logs

Digitizing environmental parameters is a mandatory requirement for a laboratory to achieve GMP cleanliness level certification. We need to install automatic sensors to record differential pressure, temperature, and humidity in real time.

The data is automatically stored on a closed management software and cannot be manually edited or deleted. This log ensures absolute reliability when presented to GMP inspection teams.

Conclusion

Implementing the correct HVAC system design process and differential pressure control is the core foundation for the safe operation of a microbiological cleanroom. Controlling ACH and temperature/humidity, maintaining a positive differential pressure gradient of +10 Pa to +15 Pa, integrating LK Lab microbiological culture cabinets, planning for 82-inch angled pressure tables and specialized Duc Duong sinks, preventing pressure drops via airlock interlocks, and adhering to a regular inspection schedule all aim to achieve GMP cleanroom standards. This sophisticated system helps the facility meet the stringent criteria for the four cleanliness levels in GMP factories. Simultaneously, the lab will consistently maintain optimal GMP cleanliness levels to pass all audits. Duc Duong Company is proud to be a reputable general contractor, providing high-quality HVAC design consulting solutions and cleanroom equipment.

Customers requiring consultation on 3D HVAC layout design for microbiological cleanrooms and price quotes for laboratory equipment, please contact and register at DUC DUONG SCIENCE AND TECHNOLOGY COMPANY for dedicated service.

 

 

 

DUC DUONG SCIENCE AND TECHNOLOGY COMPANY

Address: 1014/67 Tan Ky Tan Quy, Binh Hung Hoa Ward, Binh Tan District, Ho Chi Minh City

Tel: (028) 3762 8042 – 3762 8043 – 3750 8514 – 3750 8793

Fax: 028 37628043

Email: ducduong@ducduongco.com

Website: ducduongco.com

ZALO OA: DUC DUONG SCI

 

FAQ

1. Why is it mandatory for microbiological cleanrooms to maintain a positive pressure gradient?

A positive pressure gradient of +10 Pa to +15 Pa creates a forced aerodynamic barrier. When the air damper is open, high-pressure clean air from the microbiological culture room will flow progressively into the buffer room, completely preventing fine dust and suspended microorganisms from the outside environment from entering and damaging the agar plates.

2. What is the difference between a fixed airflow (CAV) system and a variable airflow (VAV) system in a cleanroom?

The CAV system provides a continuous, constant airflow, suitable for cleanrooms operating 24/7 stably. Meanwhile, the VAV system automatically adjusts the fan and damper speed based on pressure fluctuations and the number of personnel, significantly saving electricity costs for AHU operation but requiring a highly accurate sensor system.

3. How does the LM-1800V vertical airflow microbiological culture cabinet support the cleanroom HVAC system?

The LM-1800V microbiological culture cabinet distributed by Duc Duong integrates a HEPA H14 filter that removes >= 99.995% of 0.3 µm dust particles, creating a localized Grade A (Class 100) ultra-clean zone right at the work table. The device operates independently without affecting or disrupting the general convective airflow of the central HVAC system.

4. Why is it necessary to place the return air vent close to the wall in a microbiological cleanroom?

Fine dust and microbial spores tend to settle due to gravity and airflow from the ceiling. Placing the return air vent close to the wall (0.1 – 0.2 m from the floor) helps to draw all dust particles downwards and into the filtration system without being recirculated back into the culture chamber.

5. What HVAC system performance indicators are evaluated in the Cleanroom Recovery Test?

The recovery test measures the time it takes for the AHU/HVAC system to automatically clear dust and dirt and return the cleanroom from an in-operational state to an at-rest state. GMP standards stipulate that the ideal recovery time should be between 15 and 20 minutes.