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OfflineRnb1987
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Registered: 10/16/19
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Flowhood question-fan placement
    #27996137 - 10/12/22 10:01 PM (1 year, 7 months ago)

So I’m finally getting around to building my flow hood. Unfortunately, I made the box a little bit smaller than I should  have and the depth is The exact same size as my fan if I placed the fan in the center of the back.  I wanted to build an enclosure around the fan but I don’t have a whole Lot of room... if I turn the fan sideways I have just enough room to build something around it but with the fan sideways it is right up against the back of the filter.

Box is 26x26x16
Filter is 6in deep
Fan is 10x16



My question is does it matter where I put my fan in relation to the filter? 

I would just like to have a little area on top of the hood to be able to set things on and I’m seeing what my options are

Thanks:mushroom2:


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OfflineTheUsualSuspect
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Registered: 09/11/22
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Re: Flowhood question-fan placement [Re: Rnb1987]
    #28002543 - 10/17/22 12:44 AM (1 year, 6 months ago)

I built a flow hood and recently re built it. In that process Ive learned a few things.

First, since I hadnt done this before I did like usual and went P for plenty. I used 3/4 inch plywood, wood glue, high torque deck screws.... you get the picture. Thats a cute idea except 1) its heavy as fk. If I dropped it on you, you might die. 2) building it like heirloom furniture to be used at rugby matches means when you have to alter it because the design is screwed up, good luck. I had to beat it apart with a chisel and mini sledge cause wood glue is quite a bit tougher than wood. I should have built it WILDLY lighter wall construction.

Second, I used the wrong filters. I shopped a LOT before buying the filters and the mirv 16 filters I bought were large and good particle size but were designed for furnace use, not lab clean air environment. They did work correctly for the times I used the box with them installed but was it partly luck, or short lifespan about to run out? I dont know. I decided to replace the filters at the point I realised I made a mistake.

When I first built it, instead of a blower like most people use, I bought a blower unit from home depot:
https://www.homedepot.com/p/B-Air-1-8-HP-Air-Mover-Carpet-Dryer-Floor-Blower-Fan-for-Home-Use-in-Blue-BA-VP-15-BL/318199179

After building the unit, I realised I had a hot spot in the middle of the filter and none on the outside of the filters (I had 2 filters, 25x20 side by side). My theory at the time was I needed more air flow even though the air coming out was fairly high pressure. I upgraded to this:
https://www.homedepot.com/p/B-Air-1-2-HP-Air-Mover-for-Janitorial-Water-Damage-Restoration-Stackable-Carpet-Dryer-Floor-Blower-Fan-in-Grey-BA-VP-50-GY/301053818

Problem was, the filters had no restriction to them, they were the wrong kind so when I boosted from 1/8 hp to 1/2 hp, had no effect but making the hot spot much worse with dead zones on the side. Thats when I realised I would need 2 things, the correct type air filter (that has a flow resiriction) and a internal baffle to spread out the air.

I got this air filter off ebay, and I was so happy with the price AND NO SHIPPING CHARGE I bought 2, one for now and 1 in case I need a backup:
https://www.ebay.com/itm/154110329556

Spent an afternoon making a new front for the flow hood adapting the old hole to the new filter size. The internal baffle I had to try a couple versions, the last worked.

After going through the effort I can see if you can get a new, premade fan filter unit 2 ft x 4 ft like the medical ceiling mount units for say 650-850 all in, to me thats worth the hastle. If you are building your own, make sure you build it in a way that its alterable after the build so you can dial it in.

With a box as small as you built and the size of blower and the filter, I think any way you can shoehorn the blower onto the top will be fine. I wouldnt be surprised if you end up needing to install some kind of baffle to spread out the air flow so its even. Maybe, maybe not.

I dont currently have a pre filter in front of the blower but I use it in a very small room with tile floor and one of those giant box cube filters running 24/7 next to it. The room air is pretty clean to start with.

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Offlinelivelogikal
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Re: Flowhood question-fan placement [Re: TheUsualSuspect]
    #28005606 - 10/18/22 10:44 PM (1 year, 6 months ago)

Get yourself a reastat to dial in the speed of your fan to establish actual laminar flow. Build a prefilter shroud and you should be good. The test is if you can get a lighter flame to bend 90 degrees with minimal flutter this is where you will use the reastat to build up your static pressure! Looks like you have potential there don't start over. Yet.

Edited by livelogikal (10/18/22 10:58 PM)

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OfflineRnb1987
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Re: Flowhood question-fan placement [Re: TheUsualSuspect]
    #28006952 - 10/19/22 07:34 PM (1 year, 6 months ago)

The usual suspects Thank you for sharing your insight. I think the baffle idea is great. I was worried about the air blowing right up against the side of the filter but with something to redirect the air a bit that would solve the problem.

When you remade your hood did you use a different material on the outside?

This thing is HEAVY! I used 1in thick FRP panels that I got from a restaurant I was building. I was considering using 1x2 and 1/4 ply instead honestly

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OfflineRnb1987
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Re: Flowhood question-fan placement [Re: livelogikal]
    #28006959 - 10/19/22 07:39 PM (1 year, 6 months ago)

Quote:

livelogikal said:
Get yourself a reastat to dial in the speed of your fan to establish actual laminar flow. Build a prefilter shroud and you should be good. The test is if you can get a lighter flame to bend 90 degrees with minimal flutter this is where you will use the reastat to build up your static pressure! Looks like you have potential there don't start over. Yet.




I don’t love the idea of installing One of those. I was however planning on building a fan shroud with a 12x12 prefilter in an air return grate. I’m hoping that will dial it back a little. I think my fan is a bit overpowered but it was free:cool: we shall see...if I ever get back to it. Thank you

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OfflineTheUsualSuspect
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Registered: 09/11/22
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Re: Flowhood question-fan placement [Re: Rnb1987]
    #28007159 - 10/19/22 09:31 PM (1 year, 6 months ago)

Quote:

Rnb1987 said:

When you remade your hood did you use a different material on the outside?






The original box was built specifically so 2 of the 25x20 filters side by side would press fit into the front (25x40). That was not a good plan. I should have made it so they slide in easily because I had to remove them 3 or 4 times and they almost ripped moving them. Outer box was externally 3/4 inch plywood with 2x2 in the corners, screwed and wood glued. I used the same external housing in the rebuild but made an insert screwed into the front mouth to accommodate the replacement filter which was slightly smaller. If I made another im sure I would downsize that outer housing to 1/4 inch plywood. All it has to do is get full of air and not let the filter move out of the way.

I used that silver metallic ducting tape to seal the edges all around the edge of the filter to box fit so I wouldnt have to worry about contamination leaking out.

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OfflineTheUsualSuspect
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Registered: 09/11/22
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Re: Flowhood question-fan placement [Re: TheUsualSuspect]
    #28007182 - 10/19/22 09:46 PM (1 year, 6 months ago)

Here is a side pic of the unit. I have it in a grow tent to make a low tech clean room.


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