9.5.1. Cleanroom Ceiling Mounted Terminal HEPA Filter Systems
When selecting HEPA Filters For Commercial or Industrial Cleanroom Applications, many of the same rules apply to the process as are used in selecting HEPA filters for Medical or Biological applications. Cleanroom manufacturing processes require High Purity air filtration to protect the raw materials and the end product from particulate that can damage the product or cause it to fail in use.
Examples of industrial operations that rely on Cleanroom HEPA Filters include:
Cleanroom HEPA Filters Selection Factors - Industrial Cleanroom HEPA Filter Selection should be guided by factors such as:
Cleanroom HEPA Filter Systems Guide
The ISO 14644-1 Document Classifies Cleanrooms based on Particles per Cubic Meter at various particle sizes, according to the following Chart:
Cleanroom HEPA Filter Selection
Selection of the optimum number of HEPA filters for any given cleanroom is related to the Classification of that specific cleanroom and the Ceiling Coverage required to produce the number of air changes for the targeted level of cleanliness, generally in accordance with the recommendations below:
1. Actual average velocity and air changes required may vary depending on the application and floor plan.
2. ULPA (99.999%) HEPA filters required on Class 1/10 application, HEPA (99.99%) required on all others.
3. Figures assume standard airflow capacity of 650 CFM for a 24" x 48" HEPA filter module.
Converting the ratios into actual Recommended Numbers Of Standard Size 24" x 48" (Nominal) Ceiling Modules or HEPA Fan Filter Units, the chart below assists with the selection process:
As can be seen in the charts, Class 1-2 applications require up to 100% ceiling coverage of HEPA fan filter units, Terminal HEPA filter units or Ducted Terminal HEPA Filter units to produce a laminar or uni-directional flow of clean air traveling downward at a velocity of approximately 90 feet per minute, as measured 6" below the filter face.
This design ensures a positive pressure inside the cleanroom, which prevents the infiltration of contaminants and also provides for the removal of particles generated by people and equipment in the work space.
Cleanroom HEPA Filter System Air Change Rate
Another important criterion is Air Change Rate - The ability of a system to move a volume of air through the system in a given time is usually expressed as air changes per hour. Because of the unusually high air change requirements of cleanrooms, the general air change requirements defined by ASHRAE standard 62.1 for occupied spaces is not relevant. Those air change rates are based on removal of CO2 and on occupant comfort.
In a cleanroom, the driving factor is contaminant removal and cleanliness level. Many cleanrooms also have stringent temperature and humidity tolerances, and may require humidification or dehumidification as part of the HVAC system. These systems, along with the HEPA filters, must be selected with attention given to operating pressure drop, energy efficiency and ease of maintenance.
Cleanroom HEPA Filter System Lifespan
HEPA Filters for Cleanroom environments can have a life span of 3-15 years or more, based on how well protected they are from larger particles and how well maintained the cleanroom is. Room-side replaceable HEPA filter modules are available in most applications. These HEPA modules allow replacement of the HEPA filter within the module, from the cleanroom side of the ceiling space. This eliminates the need to break the critical ceiling barrier, which would contaminate the cleanroom.
In addition, HEPA filter modules can be ordered with integral light fixtures for cleanrooms where most of the ceiling space is loaded with HEPA filters and there is no room for standard light fixtures. These Flow-Through HEPA Fan Filter Units or Side-Integrated Light Fixture HEPA Fan Filter Units are an economical choice, reducing wiring costs and saving space. Often, the HEPA filter pack depth is increased to accommodate the small HEPA face area with the Side-Integrated models.
Other Important Features Of HEPA Filter Modules For Cleanrooms
Cleanroom HEPA Filter Protection and Performance
Protection of HEPA filters in Cleanroom applications is a critical design decision. It is recommended that prefilters be at least MERV 8, 30-40% ASHRAE dust spot efficiency. Pleated air filters and 3-Ply Ring Panels/ Link Panels work well in this instance.
It is further recommended that final filters be installed between the prefilter and the HEPA filter, and that they have at least a MERV 13, 85% ASHRAE dust spot efficiency rating. Box Filters or Pocket Filters are ideal for this application. Alternatively, if space inside the air handling equipment is limited, you can select a Minipleat in a 4" depth that has a MERV 13, 85% rating as well. The life cycle will be shorter than the 12" or 6" deep box filters, or the 12´-36 " deep pocket filters, but you will be able to achieve the higher efficiency in the absence of deeper final filter space.
Be Sure To Select The Optimum HEPA Filter / Filtration Equipment For Your Cleanroom
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