Abstract: This article presents the key aspects of designing an air-conditioning system for a Class 100 clean laundry room, including the main design parameters and system type. It emphasizes the economic and technical advantages of using dry coolers in high-grade cleanrooms, offering insights into their application and performance.
Keywords: clean room, air conditioning design, dry cooler, ventilation, high-efficiency filter
1. Introduction
With the continuous advancement of cleanroom technology, the demand for higher cleanliness levels has increased significantly. Cleanrooms with classifications such as Class 100, 10, and 1 are now widely constructed. Improving the cleanliness level means stricter control over environmental conditions. A comprehensive approach is essential to maintain cleanliness throughout the entire facility, including supporting areas. This project involves a Hong Kong-owned clean laundry room located in Dongguan City, classified as Class 100 (with some areas at Class 10). The laundry room occupies 1,030 m² on the ground floor of a three-story building. The first floor includes a Class 100 packaging area, a test workshop, a Class 10,000 laundry area, a dressing room, office space, warehouse, and several specialized rooms. The total clean area is 355 m², with 195 m² at Class 100 and 160 m² at lower classes. The system adheres to the standards set by the US Federal Standard 209E. Refrigeration and steam boiler systems are separate.
2. Main Design Parameters
Based on the requirements from the client and the guidelines of FS209E, along with reference to the "Clean Plant Design Code" GBJ73-84, the following parameters were established. See Table 1.
3. Clean Air Conditioning System Design
3.1 Cooling Load for Class 100 Cleanroom
The cooling load in summer includes heat transfer through walls, personnel, lighting, equipment, fan operation, and fresh air. Calculations show that the cooling load for the Class 100 dry/packaging area is 1,020 W/m², 1,000 W/m² for the test area, and 887 W/m² for the laundry area.
3.2 Air Conditioning Mode for Class 100 Cleanroom
The system uses a PAHU + DC + FFU configuration, as shown in Figure 2.
Figure 2: Schematic of Class 100 Cleanroom Air Conditioning
In this system:
- PAHU: Primary Air Handling Unit
- DC: Dry Cooler
- FFU: Fan Filter Unit
The PAHU ensures positive pressure and humidity control. Fresh air volume is 1,500 m³/h, with a heater and humidifier installed. Multiple dry coolers are used in each workshop. These coolers do not condense, which helps avoid moisture buildup and bacterial growth. Advantages include reduced machine room space, simplified control, better temperature regulation, lower noise, and no condensation issues. However, the initial investment is higher due to the need for higher water temperatures and additional heat exchange systems. Despite this, it's more economical than traditional AHU systems for high-class cleanrooms.
The FFU circulates air, mixes it with fresh air from the PAHU, and distributes it through HEPA or ULPA filters. Due to limited ceiling height, airflow is organized via upper and lower side vents.
3.3 Air Conditioning for 10,000-Level Dressing Room and Laundry Area
This area uses an AHU + final high-efficiency filter system, as shown in Figure 3.
Figure 3: Schematic of 10,000-Class Cleanroom Air Conditioning
3.4 Fresh Air and Supply Air Volume
Fresh air volume is determined by either human hygiene needs or maintaining positive pressure. The larger value is chosen. For the Class 100 cleanroom, the FFU passes through the dry cooler. Due to low temperature difference and fan pressure, the pressure drop must be less than 50 Pa. In this project, it’s 30 Pa. Air supply volume also considers cooling load and enthalpy differences.
3.5 Air Treatment
Fresh air is heated and humidified by the PAHU before being cooled by the coil. During summer, the unit adjusts humidity to ensure indoor comfort. The humidifier uses electric heating and RO water. Return air is cooled by the dry cooler, mixed with fresh air, and sent through FFUs. The process is shown in Figure 4.
The 10,000-level cleanroom follows a standard air treatment process. After mixing, the air is cooled and sent to the room.
4. Cold Source and Water System
The project covers 560 m² with a total cooling load of 374 kW. Two CARRIER 150RT screw chillers operate with R134a refrigerant, providing chilled water at 7°C/12°C. Chilled and cooling water pumps are used in parallel. A cooling tower is installed on top. The system is designed for efficiency and stability.
5. Automatic Control System
The DDC system controls humidity and static pressure. It regulates chilled water flow based on indoor humidity readings. In winter, electric heaters and humidifiers adjust conditions. Dry coolers have two-way valves and sensors for precise control. Fire detection systems integrate with the control circuit to stop fans during emergencies.
6. Commissioning and Testing
Commissioning began in late July 1999. High-efficiency filters were tested, adjusted, and replaced if necessary. Positive pressure, cleanliness, temperature, humidity, and other factors were measured. All results met the NEBB standards.
7. Conclusion
The project was completed in August 1999 and has performed well since then. Key findings include:
7.1 Dry coolers save significant space in high-class cleanrooms and offer flexible control, making them ideal for advanced applications.
7.2 Cleanrooms at this level require up to 1,000 W/m² due to strict cleanliness and equipment loads.
7.3 Attention should be given to the filtration of incoming air to ensure optimal performance.
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