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HEPA Fan Filter Unit Considerations


Sometimes it's the small details that have the largest impact...


There are a lot of decisions to be made when completing a cleanroom build and the small details can have a large impact. Project leaders frequently rely on their architect and MEP (mechanical, electrical and plumbing) group when it comes to HEPA (High Efficiency Particulate Air) Fan Filter Unit decisions. Architects and MEP groups are experts and know the air exchange requirements, however it is your Plant Operations team that must live with their HEPA Fan Filter Unit solutions for managing those cleanroom spaces. To that end, below are a few things to consider when planning early stage HEPA fan filter unit discussions.


How many air exchanges do YOU desire, over and above what the regulations require? 

It is the pharmacy department’s obligation to communicate these regulations/needs early. The MEP personnel will usually refer to the regulations and their past projects when choosing the number of air exchanges. Pharmacy Directors often prefer more than the minimum air exchanges to combat spore growth. This change may dictate additional engineering, more expensive equipment, and even increased overhead space requirements. Our experience with cleanroom regulations has taught us that one regulation’s minimum is often considered non-compliant when the next regulation update is rolled out.


How do you want your Plant Operations personnel to service the fan units once in operation? 

Servicing fan units can be an extremely disruptive process if this is not considered when designing a cleanroom. Different models and brands of fan units have different methods of service, so it is important that service preference is communicated at the beginning of a project.


Some fan units only can be adjusted from the ceiling overhead spaces, while others can be fully serviced from inside the room. If the unit chosen must be serviced from the overhead spaces (i.e. motor replacement), you must be certain there are service access hatches adjacent to each fan unit. The service hatches must be large enough to allow equipment and service personnel needs. Otherwise, steps will need to be taken that will likely mean recertification of the space.


How does Plant Operations diagnose and manage the fan units? 

Many MEP groups have a preference on which HVAC system to use, whether that be a VAV (Variable Air Volume) system or an individual fan-controlled system (“smart” or manually controlled). In polling several leading fan unit manufacturers, their recommendation is to use VAVs in conjunction with connecting each fan unit to the facility’s BAS (Building Automation System). This allows plant operations personnel visibility to each fan unit’s operation resulting in the ability to diagnose a problem remotely for service purposes. 


It is important the correct fan unit is specified and ordered early in the construction schedule due to long lead times. 


Note: Some smart fan units are not compatible with VAV systems. Having both can result in the two systems fighting each other to control the air volume. 


How do you want your certifier to test each fan unit during recertification inspections? 

Not only is this one of the most overlooked agenda items, but it is also often neglected during the construction of a cleanroom build. Not all fan units have test ports accessible from the room side, and even if they do, it is important to examine the process that goes into accessing those ports.


Based on our experience, the best solution is to have test ports installed in the ceiling adjacent to each fan unit during the construction of the space. The certifier can easily unscrew the test port cap (often by hand/tool-less) and “smoke” the port. These ports must be installed in the supply duct about five feet above each fan unit to provide a non-turbulent sample. The probes and length of air tube should be installed into the supply duct for each fan unit, often BEFORE the ceiling grid is installed. Later, the access port itself is installed into the ceiling, attaching the end of the air tube from the duct. It can be costly to install these ports after the fact.


Whatever your desired solutions, discussions should happen a year or more before construction begins when establishing the budget, schedules, etc. They are too important to leave to chance. Like many other considerations in a cleanroom build, the ability to meet the regulations is only the starting point.


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