Double Glazed Clean Room Windows for Stable FFU Air Pressure Zones

Stable air pressure zones in FFU (Fan Filter Unit) cleanrooms are crucial in addition to the control of airborne particles. Positive (or negative) pressure will not contaminate other premises that are in adjacent areas. The positive pressure in the Operating Room with respect to the corridor shall be maintained at an Operating Room in a hospital. A pharmaceutical filling line has to have a higher pressure than the other pressure support regions around it. Pathogens must be contained within BSL-2 lab. These clean rooms have double glazed windows which play an important role in maintaining these pressure zones. They improve the FFU System's performance in the following ways:

1. Thermal Insulation Prevents Buoyancy-Driven Pressure Fluctuations

Single windows have a good heat transfer rating. If the temperature in the environment is different from the cleanroom temperature, the temperature of the inner surface of the glass should not be much higher or lower than the ambient temperature. Natural convection currents develop on the surface of the glass due to the temperature difference, the warm air is rising and the cold air is falling. These buoyancy currents are against the laminar flow created by the FFU and create the pressure variations in the air that disrupt the intended pressure cascade. Double glazed windows have 2 panes of glass (usually 6-16 mm of argon or krypton gas between the panes). This building will have thermal insulation and maintain the inner glass surface temperature near to room temperature. The thermal transmittance (U-value) of the double clear room windows of Huaao is 1.5 W/m²K compared with 5.7 W/m²K of single glazing. Double glazing helps to eliminate temperature differences which minimises any flow separation that may occur due to buoyancy and helps to ensure stable and uniform pressure zones with little variation around the FFU.

2. Condensation Control Prevents Moisture-Related Pressure Drops

Water on windows goes beyond being an eyesore! Moisture can condense on a cleanroom window and form a thin film of water which can be a source for microbial growth. For FFU systems the most important implication of condensation is that the surface of the window is cooler than the dew point of the room air. Such a temperature difference generates the same buoyancy induced flows as noted above, and can result in moisture problems in wall joints or seals that will eventually affect the integrity of the pressure.

Huaao's double glazed window are designed to be condensation free even in extreme weather. Dew point is around 11°C when air temperature is set at 22°C and humi¬dity is 50% RH in a normal hospital cleanroom. Our double glazing windows that have low emissivity (low-E) and argon gas keep the interior surface temperature of the window above 18°C under identical exterior temperature conditions. That's why it is not possible for condensation to occur. Other high performance solutions for pharmaceutical clean rooms are offered by triple glazing and warm edge spacers, which can be used to further reduce humidity (30-40%RH). Stable seals/pressure zones, dry windows.

3. Structural Stiffness Maintains Seal Compression Under Load

Pressure differentials are applied to the surface of the clean room envelope (a surface that includes windows). About 5 kg per m² of window area will be the application of a 50 Pa positive pressure (typical for ISO Class 5 pharmaceutical cleanrooms). A window has a total force of 9 kg on it and is 1.5 m high and 1.2 m wide (1.8 m²) which can cause bowing in the window glazes and result in loss of compression on perimeter seals and leak paths.

Double glazed units are extremely rigid in comparison to single glazing, and have high bending resistance as the two glass panes are attached to a spacer frame. Huaao double glazed clean room windows are made of 4 mm to 6 mm tempered glass on the two surfaces, and their heavy wall aluminum frames. When differential pressure is up to 250 Pa, the compression of seal is even and less than 1 mm about 1 mm frame deflection. This structural stability allows for pressure zones to stay stable not only when first certified but over the years of operation.

4. Acoustic Insulation Reduces FFU Noise Transmission

Acoustic insulation reduces noise transmitted from FFUs into the cleanroom. FFU system noise is between 55 and 65 dBA, depending on fan speed and the loading of the filters. This noise can interfere with patients' health, surgeons' concentration and communication in hospital cleanrooms. Single glazed windows do not block out sound effectively or from reaching the target FFU noise level, so staff have to increase his or her voice level to achieve it, and can not hear alarm sounds effectively through single glazed windows.

The level of acoustic insulation is fair in double glazing windows. Insulation effect of air gap between the panes. The double glazed windows of Huaao can be given a sound transmission class (STC) rating between 35 and 40, while single glazed windows have a STC rating ranging from 25 to 28. This is a reduction of 10-15 dB which corresponds to a 50% reduction in loudness. This acoustic advantage is particularly beneficial in hospital cleanrooms, where the patient can be awake and the staff needs to hear equipment alarms, without making changes to the FFU settings or the pressure parameters.

Summary

Four mechanisms with double glazed clean room windows ensure stable FFU pressure zones: Thermal insulation prevents buoyancy driven pressure changes, Condensation control prevents moisture degradation of the seal, Structural stiffness provides seal compression under differential load, and Acoustic insulation reduces transmission of FFU noise without affecting the FFU parameters. The double-glazed window is made by the national high-tech enterprise Huaao Clean Technology Group which has 6 factories of 250,000m2 and 800 employees with annual revenue of 1 billion RMB. For more information about your double glazed windows FFU clean room project, please contact Huaao today.