How should an air conditioning and purification system be designed for a food cleanroom?
The core design of air conditioning and purification systems in food cleanrooms is to meet the specific process requirements of different products, such as low temperature and high humidity, while controlling dust, bacteria, and cross-contamination.
I. Core Design Principles: Three Controls and Pressure Difference
Airflow "Three-Flow" Principle: Ensure directional airflow from the clean area → semi-clean area → general area. A positive pressure difference of ≥10Pa must be maintained between the clean area and adjacent lower-level areas to prevent backflow of contaminants.
Eliminating Sanitary Dead Corners: Use rounded corners and floors, and select food-grade 304 stainless steel or antibacterial color steel plates as the enclosure structure for easy cleaning and corrosion resistance.
II. Air Purification System Technical Composition
This is the most crucial hardware component for ensuring cleanliness, requiring high-level configuration:
1. Filtration System: Employs a three-stage filtration system: G4 (pre-filter) + F8 (medium-efficiency) + H13 (high-efficiency). For Class 300,000 cleanrooms, high-efficiency filters can be used at the terminal to replace high-efficiency filters to reduce resistance.
2. Air Change Rate: Class 300,000: ≥12 times/hour; Class 100,000: ≥15 times/hour; Class 10,000: ≥25 times/hour.
3. Airflow Organization: Top supply and side return or top supply and top return. Supply air vents should be distributed as evenly as possible, and return air vents should be located in corners.
4. Temperature and Humidity: Standard requirements: Temperature 18-26℃, Humidity 45%-65%. Special processes (such as cold chain) require dedicated low-temperature dehumidifiers.
III. Antibacterial and Cross-contamination Control
1. Return Air Treatment: Return air vents should be equipped with low-resistance disinfection devices, requiring a particulate matter gravimetric filtration efficiency ≥95% to prevent bacterial growth within the ductwork.
2. Local Exhaust Ventilation: If there are high-temperature, high-humidity processes or processes that generate dust/odors in the workshop, independent exhaust ventilation must be provided, and the use of recirculated air is strictly prohibited; full exhaust and full supply are required.
3. Special Process Sections: For processes such as baking that easily generate oil fumes, the air ducts must be treated to withstand high temperatures (≥120℃) and equipped with oil fume purification units.
IV. Special Application Scenarios Design
If the product involves the following processes, special design considerations are required:
1. Low-Temperature Dairy/Yogurt Filling: Since the workshop needs to maintain a low temperature of 8-12℃, conventional air conditioning is prone to frosting. A direct expansion system or a low-temperature air supply solution such as ethylene glycol is required, and the issues of low-temperature dehumidification and floor condensation must be addressed.
2. High-Humidity Cleaning Area: The floor must be constructed with at least 6mm thick polyurethane self-leveling compound and designed with a drainage slope; the walls must have a 2m high 304 stainless steel wainscoting or full stainless steel walls to resist daily CIP chemical washing.
V. Acceptance and Key Monitoring Indicators
After system construction, acceptance and daily maintenance will mainly focus on the following data:
1. Suspended Particles: Meets the corresponding classification (e.g., Class 100,000: ≥0.5μm particles ≤ 3,520,000 particles/m³).
2. Settling bacteria: For example, a Class 100,000 area typically requires ≤15 CFU/plate (Φ90mm, 0.5h).
3.. Pressure differential: ≥5Pa between rooms of different class, and ≥10Pa between clean and non-clean areas.
4. Automation and interlocks: Fan start-up and shutdown must have an interlock procedure (supply air starts first, then return/exhaust air starts), and automatic monitoring of temperature, humidity, and pressure differential is recommended.