Air flow exceed rated CFM for HEPA filter
Air flow exceed rated CFM for HEPA filter
(OP)
Hi,
We have installed HEPA filter 24x24x12" in the duct. This filter is rated for 2000 CFM, but we have actual 3800 CFM air flow at this point.
The filter is collapsed for some reason. My question is, if it is happen due the exceeding CFM or no? Does somebody have an experience.
Yury
We have installed HEPA filter 24x24x12" in the duct. This filter is rated for 2000 CFM, but we have actual 3800 CFM air flow at this point.
The filter is collapsed for some reason. My question is, if it is happen due the exceeding CFM or no? Does somebody have an experience.
Yury





RE: Air flow exceed rated CFM for HEPA filter
RE: Air flow exceed rated CFM for HEPA filter
If you plan on keeping the same airflow, expand the ductwork for the filter section (i.e., taper out to an appropriate size (maybe 42" x 24")) and back in after the filter section. Check what size of HEPA filters you can get of course and design accordingly.
RE: Air flow exceed rated CFM for HEPA filter
I haven't seen an off the shelf HEPA that handles 2,000 CFM/SF, but I've never really looked for a custom job. Static pressure would be high. If you haven't done so already, I'd recomend a prefilter and dP across each filter.
RE: Air flow exceed rated CFM for HEPA filter
Chasbean1,
You are assuming a "squared" relation between flow and pressure drop, which is of course true for most pressure losses.
However, this is not the case for a HEPA filter. These are near linear and so a doubling of the flow will result in about double pressure loss.
(Don't ask me about the physics on this one...probably got something to do with the way the filter actually captures the fine grains etc.)
RE: Air flow exceed rated CFM for HEPA filter
Zesti, really? That sort of defies logic for me...
RE: Air flow exceed rated CFM for HEPA filter
Yes, I know, it does not seem logical but it is true.
I just picked a "random" document from the TROX range:
http://
Have a look at the graphs on page 3 and 5: linear relation between flow and pressure differential.
RE: Air flow exceed rated CFM for HEPA filter
RE: Air flow exceed rated CFM for HEPA filter
The design static will be higher considering the worst case of dirty filter conditions for all filters. In case of HEPA filter when it is dirty the static will be more, whereas initially the static will be less than the design contributing to higher cfm and consequently the velocity across filter is more than design and will make the filter performance topsy turvy.
Hence it is essential to fine tune either with VFD to reduce the speed or change the motor pulley close to the design cfm and have pressure differential measured to clean or replace the HEPA filter when it becomes dirty or not cleanable situation.
RE: Air flow exceed rated CFM for HEPA filter