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| HEPA filters and fans |
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| engineheat:
Hi, I want to build a DIY air purifying system that incorporates a HEPA filter. I'm a bit confused on the different types of fans available for filtration purposes. I know there must be sufficient air pressure. When I tried to learn more about fans, I come across terminologies like "centrifugal" and "axial". The way I understand, axial fans are the common type that we are all familiar with, it can move lot of air but cannot generate high static pressure. But I'm a bit fuzzy on the terms "centrifugal", "squirrel cage", "blower". Are they all pretty much the same thing? Any of those would be suitable for a HEPA filter provided the static pressure is sufficient right? Do you know what pressure is sufficient for a HEPA filter (assuming clean filter, just need a rough ballpark idea) Thanks |
| thm_w:
We have many threads here if you search: https://www.eevblog.com/forum/reviews/(my-diy)-smoke-absorver-filtering-for-soldering/ https://www.eevblog.com/forum/projects/diy-20lt-drum-solder-fume-extractor-(hepa-active-carbon)/ https://www.eevblog.com/forum/reviews/fume-extractor-advice/ https://www.eevblog.com/forum/beginners/pwm-fan-frequency-different-from-speed-controller-frequency/ https://www.eevblog.com/forum/projects/diy-high-performance-solder-fume-extractor/ Squirrel cage is centrifugal, although usually when people say that it tends to be the wide bladed style. You probably want static pressure of 20mm H20 or more, 120mm or larger. Depending on what you are trying to do. Ideally you can get a good powerful inline duct fan and have it somewhere far away where the noise is not an issue. But if you are designing a box sitting beside you, might be different choice of fan. |
| Neutrion:
I think squirrel cage is only in the rare cases called centrifugal, where the air goes in into the middle and gets blown outward. While the fan which is normally called squirrel cage you find in fancoils often just "spoons" the air and it does not go into the middle, and can not produce too high pressure. A really good fan for such a project is to get a used IBM blade server fan(K3G180-AC40-07), which is a top notch industrial fan from EBM-Papst. It is with a BLDC motor and the controller, and you can get it for a much lower price than what such a thing would normally cost new. You can get enough pressure with it on lower rpm, and if noise is not at issue, on max. power it is really powerful. I have one, and also wanted to build an air purifyer with it, and it is still on schedule, only issue is, that there is no proper documentation for the control of it. But if money is not an issue, you may can find the same fan alone with some standard interface. (Have to add that the control can be atually easily done with a variable DC voltage source as well, so if that is OK for you, than you can have a go with them) Still if someone may knows about some more detailed doc., please let me know! |
| engineheat:
--- Quote from: thm_w on March 20, 2023, 09:06:02 pm ---We have many threads here if you search: https://www.eevblog.com/forum/reviews/(my-diy)-smoke-absorver-filtering-for-soldering/ https://www.eevblog.com/forum/projects/diy-20lt-drum-solder-fume-extractor-(hepa-active-carbon)/ https://www.eevblog.com/forum/reviews/fume-extractor-advice/ https://www.eevblog.com/forum/beginners/pwm-fan-frequency-different-from-speed-controller-frequency/ https://www.eevblog.com/forum/projects/diy-high-performance-solder-fume-extractor/ Squirrel cage is centrifugal, although usually when people say that it tends to be the wide bladed style. You probably want static pressure of 20mm H20 or more, 120mm or larger. Depending on what you are trying to do. Ideally you can get a good powerful inline duct fan and have it somewhere far away where the noise is not an issue. But if you are designing a box sitting beside you, might be different choice of fan. --- End quote --- Thanks, I did briefly look over the threads you posted. I will go back and reread them to digest later. A lot of the links in the first thread are broken, due to age, but I did notice he bought an "inline duct fan" on Ebay. You also mentioned "inline duct fan." Based on my research, "inline duct fans" are not necessarily centrifugal. Some of them are axial type. Is that right? Someone else I know built a DIY air purifer using an "inline duct fan" from AC Infinity: https://acinfinity.com/inline-fan-systems/ Looking at the T6 model, it seems pretty quiet (32 dba) but I'm not sure if the static pressure (503 Pa) is sufficient for a HEPA filter. I did some research on fans, and it seems centrifugal fans generates higher static pressure than axial. I took apart a commercial HEPA air purifier and it uses a centrifugal fan (squirrel cage) fan too. I found a company called Delta Fans that makes a wide array of DC centrifugal fans with a wide range of flow rate and static pressure. Have you or anyone heard of them? I do want to buy quality components for my project. So right now, I'm deciding between an AC Infinity "inline duct fan" vs a DC centrifugal fan from Delta, to build a home air purifier for a 800 sq ft room. But it seems the Delta fans are pretty small, their flow rates only go up to 129 CFM or so and the noise (70 db) seems pretty high. https://www.delta-fan.com/pfb0812ee-e.html But that's because I chose one with a pretty high static pressure (6 water in, or 1500 Pa). Not sure if that's way too much for what I need... Thanks |
| thm_w:
Yes inline duct fans, the small ones, are usually not centrifugal. Some of the larger units are. Either way they have decent static pressure, as they are expected to be used in long ducts. 500Pa is ~50mm H2O which should be fine, as long as the HEPA filter is not tiny (high restriction to flow). The Delta one is a crazy high RPM high performance fan, sure performance is good, but the noise (screaming sound) isn't really worth it. |
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