Change of HEPA Filters
Change of HEPA Filters
(OP)
Is it true we muss change HEPA filter if there is a change in the pressure of the filter of 10%?
Which standar have the information about that?
Thanks a lot?
Sergio
Which standar have the information about that?
Thanks a lot?
Sergio





RE: Change of HEPA Filters
RE: Change of HEPA Filters
However, I'm confused about the mention of air changes. Air flow rates should not change with filter loadings. That is what is meant by "if the fan supports" - whether the fan and motor can maintain the same airflow despite higher pressure drops. In that respect, a 10% change in airflow may be a maximum limit to change the filter. (If even that much is acceptable.)
RE: Change of HEPA Filters
If, for a constant speed system, the fan is designed at the expense of initial higher flowrates than required then the conditions can be maintained though the filters load up. The pharmacopeial requirement of no. of ACPH for class 10000 is mere 20 and for class 100000 it is 10. If the studies show the particle concentration below the class limits, air flowrate never matters.
Interestingly, HEPA efficiencies go up as they get loaded.
RE: Change of HEPA Filters
However, I think allowing airflow rates to change is peculiar to the application you cite. Most clean rooms and other applications that require HEPA filtration also have a critical dependence on air velocities and pressure differentials within the space. Airflow rates significantly affect those parameters. Ideally, the system is designed with components that allow flexibility. However, the loading of any filter is gauged by its pressure differential.
Perhaps your situation is one where you may judge HEPA loading by the affect on airflow rates (changes), or claim that "air flowrate never matters." That is not a luxury that some of us can afford.
RE: Change of HEPA Filters
RE: Change of HEPA Filters
In that case, if they have recommended no more than a 10% pressure drop in their HEPA filters, then I would take them at their word.
However, much of what Quark and I have been telling you about HEPA filters is true. So, I would definitely put your 10% requirement in the category of a vendor's "gotcha" - one of those interesting bits of info that you wish you knew before someone bought it.
RE: Change of HEPA Filters
RE: Change of HEPA Filters
I tend to think the vendor did not understand the difference, and just remembered the 10% figure.
P.S. Since the cross-sectional areas of an installed HEPA filter would not change, a % drop in air quantities would be seen as a % drop in velocity. So, quark's last post is correct, too.