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Floor dryer as air cleaner

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Forum topic by Rhaugs posted 01-12-2019 04:51 PM 239 views 0 times favorited 8 replies Add to Favorites Watch
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Rhaugs

4 posts in 10 days


01-12-2019 04:51 PM

got myself one of these floor dryers recently and im looking to turn it into an air cleaner. Plan is to encase the unit in a mobile “box” with air filters on all sides (and use it as a base for my belt/disc sander). A couple questions… will it work as is, or do I need to take off the plastic case? It has 3 speeds, which is the best setting to use? I plan on shimming the outlet a bit, so it blows at an up angle.


8 replies so far

View Mike_D_S's profile

Mike_D_S

557 posts in 2455 days


#1 posted 01-12-2019 05:06 PM

It’s more or less a typical squirrel cage setup. The plastic case is part of the fan, so if you pull the motor and fan cage out of it it won’t blow anymore.

Also I wouldn’t put filters all the way around, just on the opposite side of the exhaust. Part of what will make it effective as an air cleaner is getting a good current induced in the room to move the air back to the fan. Having intake filters on the exhaust side will rob a little of that performance due to direct recirculation.

-- No honey, that's not new, I've had that forever......

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Rhaugs

4 posts in 10 days


#2 posted 01-12-2019 05:36 PM

This was the idea behind the 4 sided filters.. you think only 1 or 2 sides would be best?

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Mike_D_S

557 posts in 2455 days


#3 posted 01-12-2019 08:32 PM

So first off, I’ll start with saying everything below is just my personal opinion and thoughts. In my opinion, the design above is more based on what looks good as compared to maximizing filtering in as much of the shop volume as possible.

The average velocity of air flow is based on the cross sectional area of the duct. The volume of air moved will be defined by the fan. So let’s say the fan is 1600 CFM exhaust, then the incoming volume is the same. So if the filters are 24”x24”, then each is 4 sq ft, for 16 sq ft total. 1600 CFM / 16 sq ft = 100 ft/min (theoretical) for the average velocity at the filter face. Which assumes the air flow is evenly distributed, which we know is not really right

100 FPM is pretty low and coming in from all four sides means that you probably are not going to be getting good airflow from very far from the filters. This doesn’t count other benches, etc which will disrupt the airflow to the unit.

Going to one filter increases the theoretical velocity to 400 FPM at the filter face. Placing the filter opposite the exhaust helps to create a circular flow where the exhaust blows one way which will tend to push air to the wall so it recirculates around the outside of the room so the intake on the other side can draw it back in.

The fact it’s on the floor will make it less effective overall due to the disruptions the rest of the stuff on the floor cause in the air flow, which is why most of these type of units hang from the ceiling.

If you only want localized filtering close to the unit, then the design above will work effectively in the near area, but if you are thinking to emulate a ceiling mounted filter to take the fines out of the air in as much of the shop as possible, in my opinion its not a suitable design.

Mike

-- No honey, that's not new, I've had that forever......

View jutsFL's profile

jutsFL

162 posts in 82 days


#4 posted 01-12-2019 09:03 PM



So first off, I ll start with saying everything below is just my personal opinion and thoughts. In my opinion, the design above is more based on what looks good as compared to maximizing filtering in as much of the shop volume as possible.

The average velocity of air flow is based on the cross sectional area of the duct. The volume of air moved will be defined by the fan. So let s say the fan is 1600 CFM exhaust, then the incoming volume is the same. So if the filters are 24”x24”, then each is 4 sq ft, for 16 sq ft total. 1600 CFM / 16 sq ft = 100 ft/min (theoretical) for the average velocity at the filter face. Which assumes the air flow is evenly distributed, which we know is not really right

100 FPM is pretty low and coming in from all four sides means that you probably are not going to be getting good airflow from very far from the filters. This doesn t count other benches, etc which will disrupt the airflow to the unit.

Going to one filter increases the theoretical velocity to 400 FPM at the filter face. Placing the filter opposite the exhaust helps to create a circular flow where the exhaust blows one way which will tend to push air to the wall so it recirculates around the outside of the room so the intake on the other side can draw it back in.

The fact it s on the floor will make it less effective overall due to the disruptions the rest of the stuff on the floor cause in the air flow, which is why most of these type of units hang from the ceiling.

If you only want localized filtering close to the unit, then the design above will work effectively in the near area, but if you are thinking to emulate a ceiling mounted filter to take the fines out of the air in as much of the shop as possible, in my opinion its not a suitable design.

Mike

- MikeDS

This sounds perfectly logical to me… If it were my build, id be following this advice.

-- I've quickly learned that being a woodworker isn't about making flawless work, rather it's fixing all the mistakes you made so that it appears flawless to others! Jay - FL

View ArtMann's profile

ArtMann

1220 posts in 1057 days


#5 posted 01-12-2019 09:24 PM

The intake air will be slow but the output will provide plenty of circulation velocity for the filter to work. You just need to choose the discharge direction carefully. I think your original approach is better because it doesn’t restrict the air flowas much. What matters is the total cfm and it will be greater with more filter surface area. I know this because I used a blower similar to yours and built a filter like Mike suggested. One filter greatly reduced total air flow. The 1600 hypothetical cfm might be reduced from 1600 to 200 – 400. Filters that will trap 1 micron particles like you want are very restrictive.

View Rhaugs's profile

Rhaugs

4 posts in 10 days


#6 posted 01-12-2019 09:32 PM



So first off, I ll start with saying everything below is just my personal opinion and thoughts. In my opinion, the design above is more based on what looks good as compared to maximizing filtering in as much of the shop volume as possible.

The average velocity of air flow is based on the cross sectional area of the duct. The volume of air moved will be defined by the fan. So let s say the fan is 1600 CFM exhaust, then the incoming volume is the same. So if the filters are 24”x24”, then each is 4 sq ft, for 16 sq ft total. 1600 CFM / 16 sq ft = 100 ft/min (theoretical) for the average velocity at the filter face. Which assumes the air flow is evenly distributed, which we know is not really right

100 FPM is pretty low and coming in from all four sides means that you probably are not going to be getting good airflow from very far from the filters. This doesn t count other benches, etc which will disrupt the airflow to the unit.

Going to one filter increases the theoretical velocity to 400 FPM at the filter face. Placing the filter opposite the exhaust helps to create a circular flow where the exhaust blows one way which will tend to push air to the wall so it recirculates around the outside of the room so the intake on the other side can draw it back in.

The fact it s on the floor will make it less effective overall due to the disruptions the rest of the stuff on the floor cause in the air flow, which is why most of these type of units hang from the ceiling.

If you only want localized filtering close to the unit, then the design above will work effectively in the near area, but if you are thinking to emulate a ceiling mounted filter to take the fines out of the air in as much of the shop as possible, in my opinion its not a suitable design.

Mike

- MikeDS

So if I mounted this on the ceiling, would it work on its side? Or would that restrict the air flow too much since it would only be pulling from one side and not two (of the actual blower motor). If I had to mount it vertically I’d be worried it would hang down too far.

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Rhaugs

4 posts in 10 days


#7 posted 01-12-2019 10:10 PM

I do have this one mounted on the ceiling already

View CaptainKlutz's profile

CaptainKlutz

717 posts in 1735 days


#8 posted 01-12-2019 10:28 PM

Comments:

Yes, it can work. Requires some thought on design.

1) That style of squirrel cage blower loses a lot of cfm as static pressure increases. It has massive airflow/cfm with zero intake restriction. As soon you add filters, the cfm drops quickly. In order to keep the cfm/efficiency high, and have best filtration, need to maximize the filter surface area/minimize the filter pressure loss as they get dirty. This is why this fan design in never used for wood working dust collection via duct work, but can be made to work as fine dust filtration box similar to project that OP posted above.

2) While above discussion on filter flow rates is interesting, it misses one point. Filter flow rate is irreverent except to know when to replace/clean the filter, or to insure low static pressure thru blower. Thorough air filtration requires understanding of air/dust circulation in room. Goal is to circulate the entire shop air around/through the filter assembly, not have highest intake pressure (so it vacuums the room – because it can’t).

3) Mounting location is huge quandary, and source of much debate. Best location for any air filtration is where the air is guaranteed to be flowing. In commercial filtration booths, they use down-draft or up-draft designs and pull all air thru grates, into ducts and filters which bring air back to opposite side of room. Side draft designs exist where either room or duct work is oval race track where a filter wall is created and 100% of air flows horizontally thru the filter wall and around other side of room.
Doing same thing in garage or basement wood shop is near impossible without huge budget.

So best you can hope for is to buy/build a air circulation box that fits into your space, and helps to cycle shop air around the room, filtering out small dust particles in process. Air filtration is a trial and error process even for the experts doing 3D simulations to create clean rooms.
Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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