Easy & Cheap Stainless Vent Hood

[schematix]

I was talking to a buddy and he wondered if insulating the vent tube would help move the vapors out so that it doesn't cool fast and create water?

Disclaimer: I am thinking out loud here.

I am thinking the cause of the condensation in the fan is due to the increased pressure inside the housing. If you look at a phase diagram of water you'll see that if you have steam at 100C and 1atm (which is what we have), that you can condense it back to liquid just by upping the pressure a little.

I have a friend who is very knowledgeable on steam systems. I'll run this by him and see what they do industrially to prevent this. I know steam condensation is a very dangerous problem if handled incorrectly (e.g. blowing out the end of a pipe when you have an eblow).

 

[fman872]

Wow yours is full of water. I had little droplets raining out but nowhere near that much. It looks like yours has a lip right on the inside that is holding the water. Maybe drill some pin holes in the lip so it drains? My vortex fan has smooth edges so it drips freely.

I am running my boil at 65% of 5000W for a 10G batch (11.5-14G in the kettle).

I think im going to cut the lip off entirely and boil at a lower percentage. Back to workshop. I'll report back next brew day

 

[schematix]

I spoke to my buddy who deals with industrial process control systems and got his take on this set up.

Key points:
1. He doesn't think my idea about the pressure causing condensation matters much here since the pressure differential created by the blower is actually pretty low.

2. He thinks the primary reason for the condensation in this system is temperature related. The fan housing and ducting is all relatively cool. There is also a lot of surface area inside the blower and 6" duct.

3. High velocity is key to minimizing condensation. He recommends getting the largest blower possible, and using 4" duct all the way to approx double the velocity vs 6". Going any smaller will have diminishing returns since the restriction will go up.

4. Expect condensation. All steam systems have to deal with this when they are operating under the boiling point. Typically it's addressed by collecting and draining.

5. Industrial steam systems typically run 24/7/365 so all the parts are rocket hot all the time, thus no condensation. During start-up and shutdown, special equipment is activated to get rid of the liquid water.

So with that said, I'm just going to seal my leaks, and attempt to collect / drain the condensation that is inevitable.

 

[theck]

I spoke to my buddy who deals with industrial process control systems and got his take on this set up.

Key points:
1. He doesn't think my idea about the pressure causing condensation matters much here since the pressure differential created by the blower is actually pretty low.

2. He thinks the primary reason for the condensation in this system is temperature related. The fan housing and ducting is all relatively cool. There is also a lot of surface area inside the blower and 6" duct.

3. High velocity is key to minimizing condensation. He recommends getting the largest blower possible, and using 4" duct all the way to approx double the velocity vs 6". Going any smaller will have diminishing returns since the restriction will go up.

4. Expect condensation. All steam systems have to deal with this when they are operating under the boiling point. Typically it's addressed by collecting and draining.

5. Industrial steam systems typically run 24/7/365 so all the parts are rocket hot all the time, thus no condensation. During start-up and shutdown, special equipment is activated to get rid of the liquid water.

So with that said, I'm just going to seal my leaks, and attempt to collect / drain the condensation that is inevitable.

Would it help then to insulate the lines?


-------------------
Also, curious about a 8" fan like, not much more than the 6" but cheaper than those other ones people are snagging and going from 8" to 4" right away?
http://www.amazon.com/dp/B005KMUHWY/?tag=skimlinks_replacement-20

 

[schematix]

Insulating your ducts would only help if you had an issue with condensation in your ducts. Point is, if you make your air velocity high enough, condensation can be eliminated. For a short run you should be able to go without the insulation. If you had a long run it might be needed.

That style of fan is better as a booster fan in your house. For example if you need a room far from your main blower to get better airflow. They develop very little static pressure so they don't move much air once duct is attached. Their actual air flow is WAY below what they are rated for.

 

[fman872]

I spoke to my buddy who deals with industrial process control systems and got his take on this set up.

Key points:
1. He doesn't think my idea about the pressure causing condensation matters much here since the pressure differential created by the blower is actually pretty low.

2. He thinks the primary reason for the condensation in this system is temperature related. The fan housing and ducting is all relatively cool. There is also a lot of surface area inside the blower and 6" duct.

3. High velocity is key to minimizing condensation. He recommends getting the largest blower possible, and using 4" duct all the way to approx double the velocity vs 6". Going any smaller will have diminishing returns since the restriction will go up.

4. Expect condensation. All steam systems have to deal with this when they are operating under the boiling point. Typically it's addressed by collecting and draining.

5. Industrial steam systems typically run 24/7/365 so all the parts are rocket hot all the time, thus no condensation. During start-up and shutdown, special equipment is activated to get rid of the liquid water.

So with that said, I'm just going to seal my leaks, and attempt to collect / drain the condensation that is inevitable.

Hmmmm. So with a 6" fan would it be better to use 4" duct?

 

[jsprinceiii]

I believe reducing to a 4" duct will increase back pressure, and decrease CFM.
I also do not believe increasing the CFM (larger blower) is going to work.
Some suggestions..

• 6" Duct end to end, not reduced.
• Insulate the duct work.
• reduce 90 degree bends, make them 45's. This will reduce static pressure
• Make sure the vent cap is sized properly, and if it has a damper that it is functioning
• do not use a dryer vent cap.
• Makeup air inlet should be the same size or larger than exaust.
• make sure your makeup air inlet is not near the fan, preferable 10+ feet away, and lower than kettle.

 

[schematix]

I believe reducing to a 4" duct will increase back pressure, and decrease CFM.
I also do not believe increasing the CFM (larger blower) is going to work.
Some suggestions..

• 6" Duct end to end, not reduced.
• Insulate the duct work.
• reduce 90 degree bends, make them 45's. This will reduce static pressure
• Make sure the vent cap is sized properly, and if it has a damper that it is functioning
• do not use a dryer vent cap.
• Makeup air inlet should be the same size or larger than exaust.
• make sure your makeup air inlet is not near the fan, preferable 10+ feet away, and lower than kettle.

I agree with most of your points - less restriction will lead to a greater volume of air flow.

However, I don't think insulating the duct work is going to help much unless the duct is going to be in an especially cold area. There is very little heat in the steam so your duct work is going to settle just a touch above the air temperature you're pumping through it. The difference between a 50 degree duct surface and 70 degree duct surface is going to be minimal. It won't hurt anything, but I don't think for most installations its going to have a real performance benefit for the cost.

As far as 4" vs 6" velocity, all I can offer is that the air velocity was noticeably higher once the reducer was on. Sure the total CFMs went down, but now that steam was spending close to half as much time in the duct before exiting. My 4" duct was bone dry... not so much in the fan housing.

 

[schematix]

Hmmmm. So with a 6" fan would it be better to use 4" duct?

I suspect this is going to be a contentious issue, but I was told this afternoon by a licensed Professional Engineer who designs piping systems for a living (and who I consider to be an "A" grade mechanical engineer) that the best thing to do was to get the highest CFM fan possible, and use 4" duct. Counter intuitive in some regards, but the argument is that reducing duct size increases the velocity, decreases surface area, and will give less time for condensation.

My 4" ducts were pumping a ton of steam outside, and when done my 6" fan housing was dripping with water and my 4" ducts were bone dry.

 

[stickyfinger]

I suspect this is going to be a contentious issue, but I was told this afternoon by a licensed Professional Engineer who designs piping systems for a living (and who I consider to be an "A" grade mechanical engineer) that the best thing to do was to get the highest CFM fan possible, and use 4" duct. Counter intuitive in some regards, but the argument is that reducing duct size increases the velocity, decreases surface area, and will give less time for condensation.

My 4" ducts were pumping a ton of steam outside, and when done my 6" fan housing was dripping with water and my 4" ducts were bone dry.

That's a nice piece of empirical evidence. I have been using some duct calculators and the info at this site in particular:

http://custom-wheels-blowers.centralblower.com/Asset/Determining-Static-Pressure.pdf

Whenever I use 6" duct vs. 4" duct in my calculations, the actual air velocity comes out almost exactly the same (the 6" velocity is usually just a bit higher.) I wonder if there is something wrong with the calculations or if the fan I am using is just more hindered by the 4" duct (I used the fan performance curves to calculate CFM at the calc'd static pressures.)

For example, for 3 elbows, 10' of duct run and a 20 inch diameter round hood, I calculate an actual air flow of 214 and 231 FPM when using 4" and 6" duct, respectively. The 4" takes a huge hit in static pressure, which reduces the CFM, and thus the air velocity quite a bit.

My actual run will likely be 1 elbow, 4' total run and 20 in. diameter hood, which calc's out to 497 vs 508 CFM for 4" vs 6" and 228 vs 233 FPM for 4" vs 6". I shouldn't have to run the fan on full power, even for full boil (5500 W.)

This is all just calculations based upon some empirical input though, so it might all be garbage. I'm right at the point of deciding how to run and what size to use, so I think I'll just try to plan for placing my fan horizontally with the capability to have it drip on the floor if needed to be safe and use 6" duct that is well-sealed. Though, I'm tempted to switch to 4" for less space taken up and similar performance. The CFM is lower of course, but it's still really high. l The overhead might allow me to see no condensation in the fan or pipes.

 

[schematix]

I put a speed controller on my blower and it was probably a waste of $12. It can only be adjusted down maybe 20% before the steam isn't fully captured any more, and its still loud. For the 90 minutes it's on, might as well just run it full blast and use a $1 switch.

I'm not an expert in sizing blowers. I'll do some research and see if there is an explanation here.

I guess if your performance numbers say all else is equal, might as well go the cheaper route.

 

[stickyfinger]

I refurbished an old "Variac." It's super quiet from 0 - 110V and has pretty decent fan control, though, I don't know how low I will be able to run it and still get good exhausting.

 

[Hello]

I'm curious, is there any reason I could not use this duct fan through the bowl? I have the bowl, not the fan. My thought was to just do that, use ducting, then outside and buy the vent for the outside of my building.

http://www.amazon.com/dp/B005KMUHWY/?tag=skimlinks_replacement-20

 

[stickyfinger]

The manufacturer of that fan says it can be used for indoor grow rooms, but I don't know how good it would be with super high humidity conditions. If you have a short run, it might be able to move enough air. I bet it has a very poor performance curve, meaning the longer your run, the greater number of elbows and the smaller the ducting, it will drop off in CFM very quickly compared with a nicer fan. If you don't mind risking $26 to try it, it might work for a short run. I think someone else in this thread tried one or thought of trying one.

 

[theck]

I think I'm going to build a box out of 2x2s and cover the inside with galvanized duct then punch a hole in the side and use a 8" duct fan like http://www.amazon.com/dp/B005KMUHWY/?tag=skimlinks_replacement-20 not connected directly to the box but maybe a little ways off... I figure I might be able to do a drip edge as well and collect the water down a tube or ?

 

[schematix]

The manufacturer of that fan says it can be used for indoor grow rooms, but I don't know how good it would be with super high humidity conditions. If you have a short run, it might be able to move enough air. I bet it has a very poor performance curve, meaning the longer your run, the greater number of elbows and the smaller the ducting, it will drop off in CFM very quickly compared with a nicer fan. If you don't mind risking $26 to try it, it might work for a short run. I think someone else in this thread tried one or thought of trying one.

This style of inline fan has a high theoretical CFM with nothing attached, but they develop very little static pressure and so get bogged down very quickly when you put anything on them. Mfr says this 8" fan develops a mere 0.1 inH2O. The 6" vortex makes 250% more. Static pressure is your friend when you want to get high CFMs.

 

[Hello]

This style of inline fan has a high theoretical CFM with nothing attached, but they develop very little static pressure and so get bogged down very quickly when you put anything on them. Mfr says this 8" fan develops a mere 0.1 inH2O. The 6" vortex makes 250% more. Static pressure is your friend when you want to get high CFMs.

The manufacturer of that fan says it can be used for indoor grow rooms, but I don't know how good it would be with super high humidity conditions. If you have a short run, it might be able to move enough air. I bet it has a very poor performance curve, meaning the longer your run, the greater number of elbows and the smaller the ducting, it will drop off in CFM very quickly compared with a nicer fan. If you don't mind risking $26 to try it, it might work for a short run. I think someone else in this thread tried one or thought of trying one.

Oh that makes more sense now that I read about static pressure. I just saw it and thought it was an option. I'll stick to the 440 cfm vent fan that has been linked here. Thank you both.

 

[orangehero]

I've seen a small plastic tote used for the hood. Definitely easier to cut. I don't think it's necessary for it to be round or stainless.

 

[schematix]

That thin stainless bowl was a ***** to cut. Ate up 3 jigsaw blades and took about 15 minutes. Even my nice cobalt step bit was having a slow time getting my pilot hole cut.

I thought about using a plastic tote, but I have built a stainless steel shrine in by basement and didn't want to tarnish it

 

[orangehero]

Spray paint.

 

[schematix]

This is the only thing in my brewery that isn't stainless.View attachment ImageUploadedByHome Brew1423113047.444067.jpg

 

[stickyfinger]

didn't want to tarnish it

nice pun!

 

[BrewWho]

That thin stainless bowl was a ***** to cut. Ate up 3 jigsaw blades and took about 15 minutes. Even my nice cobalt step bit was having a slow time getting my pilot hole cut.

I thought about using a plastic tote, but I have built a stainless steel shrine in by basement and didn't want to tarnish it

What blades were you using?? I think the only thing i could find was a fine tooth wood blade and it ripped through it in no time!!!! Step bits seem to have trouble with ss, at least that was the case when putting holes in my keg.

 

[Minbari]

That thin stainless bowl was a ***** to cut. Ate up 3 jigsaw blades and took about 15 minutes. Even my nice cobalt step bit was having a slow time getting my pilot hole cut.

I thought about using a plastic tote, but I have built a stainless steel shrine in by basement and didn't want to tarnish it

I used a bi-metal jigsaw blade on mine. Took about 5minutes

 

[stickyfinger]

maybe it depends on the gauge of the pot, the quality of the bowls, etc. what is the approximate size of the flat, bottom part of those 30 qt SS bowls? I assume it is at least 7 or 8"?

 

[schematix]

I used Bosch bimetal fine tooth (17-22 TPI?) jigsaw blades and cut a 5 7/8" diameter hole. The bowl bottom was right at 8".

My step bit cut the Blichmann kettles like butter. On this mixing bowl it was throwing sparks and just didn't want to go.

 

[stickyfinger]

was the bowl flexing under the pressure of the bit? i fond that can cause a lot of problems unless your bit is really small. then, it will kind of pop through the metal as it flexes back.

 

[schematix]

Yep that's exactly what was happening.

 

[h22lude]

Glad I found this thread. I just put together my e-BIAB system. Right now I own a townhouse but will be buying a house relatively soon so I didn't want to do anything permanent. Anyway, I will be brewing in my bathroom. The closest window is about 15 feet away. I use a 5500W element. Would this fan work with that much duct?

http://www.amazon.com/dp/B002EC01XS/?tag=skimlinks_replacement-20

And since it is in my bathroom I will need to figure out how to build a stand for it since I can't mount it on my wall or ceiling. I like the bowl idea but a plastic box may be easier to create a stand for. Could just attach a leg to each corner and be done.

 

[stickyfinger]

Glad I found this thread. I just put together my e-BIAB system. Right now I own a townhouse but will be buying a house relatively soon so I didn't want to do anything permanent. Anyway, I will be brewing in my bathroom. The closest window is about 15 feet away. I use a 5500W element. Would this fan work with that much duct?

http://www.amazon.com/dp/B002EC01XS/?tag=skimlinks_replacement-20

And since it is in my bathroom I will need to figure out how to build a stand for it since I can't mount it on my wall or ceiling. I like the bowl idea but a plastic box may be easier to create a stand for. Could just attach a leg to each corner and be done.

I bought that exact fan recently. I haven't installed it yet, but it can really push some serious air. I think it would work perfectly for your application. It comes with a mounting bracket on the side that you can screw into a frame of some sort. You could just put four 2x4s together as legs and screw into them through a plastic tub or something and put the fan on top of that resting on the tub and then put an elbow and flexible duct on the fan. should work fine.

 

[h22lude]

I bought that exact fan recently. I haven't installed it yet, but it can really push some serious air. I think it would work perfectly for your application. It comes with a mounting bracket on the side that you can screw into a frame of some sort. You could just put four 2x4s together as legs and screw into them through a plastic tub or something and put the fan on top of that resting on the tub and then put an elbow and flexible duct on the fan. should work fine.

My only worry is condensation building up in the duct. My bathroom is attached to my bedroom which is where the window is. So the duct would start above my pot, go down to the floor and then up to the window. I would think water could build up at that low point. Not sure if that is a problem or not.

 

[stickyfinger]

I assumed your window was in your bathroom, but 15' would be a lot of bathroom i guess! i don't know. you could just try it and see what happens. you're going to have a house soon and will use the fan for sure and probably some of the duct, so why not give it a try and see. you could always poke a drain hole in the duct and let it collect in a bucket if it is a problem

 

[schematix]

Worst case when you're done tilt the duct and drain it. It's not permanent and with occasional water exposure nothing terrible is going to happen.

 

[h22lude]

I assumed your window was in your bathroom, but 15' would be a lot of bathroom i guess! i don't know. you could just try it and see what happens. you're going to have a house soon and will use the fan for sure and probably some of the duct, so why not give it a try and see. you could always poke a drain hole in the duct and let it collect in a bucket if it is a problem

It is 530CFM which is almost double what I would need. I assume the extra power would be able to handle the added duct length.

Worst case when you're done tilt the duct and drain it. It's not permanent and with occasional water exposure nothing terrible is going to happen.

Good point. Just drain and let dry.

 

[stickyfinger]

I don't know if my calcs. are correct, but assuming you have the equivalent of 3 elbows and 15' of straight duct run (using 4" duct), you would generate a static pressure of at least 0.398 in.H20 with some thrown in for the hood itself. The Tjernlund M-6 is still good for 460 CFM at that pressure.

Maybe you could mount a plastic tub over the BIAB and then poke a hole in the side, mount the fan inline on a little box or something, and then go around and out your bedroom window. it should work fine.

 

[h22lude]

I don't know if my calcs. are correct, but assuming you have the equivalent of 3 elbows and 15' of straight duct run (using 4" duct), you would generate a static pressure of at least 0.398 in.H20 with some thrown in for the hood itself. The Tjernlund M-6 is still good for 460 CFM at that pressure.

Maybe you could mount a plastic tub over the BIAB and then poke a hole in the side, mount the fan inline on a little box or something, and then go around and out your bedroom window. it should work fine.

If mounted on top I would only need one 90° elbow. The duct would go down from there, lay on the floor and then up to the window. Where my brew stand is, it is basically a straight line out the bathroom door to the window. The duct obviously wouldn't be all on the same level. From the elbow it would drop down to lay on the floor then back up to the window. The window is big, probably 2 feet from the floor.

 

[stickyfinger]

even better, i just threw in the 2 extra elbows as a worst case scenario for your floor dip arrangement.

 

[schematix]

sticky - are you always assuming a constant effective length for every elbow or are you varying it based on type and the velocity?

the right way to determine the flow you get is to first get the pump's static pressure vs CFM curve. Then you need to solve the piping systems static pressure for several CFMs and connect the points on that curve. Where the 2 curves intersect is the actual CFM you'll get. The trick here is that for every CFM and fitting you have a different velocity and different equivalent length, and a thus different static pressure loss.

 

[stickyfinger]

I'm using this document to estimate SP:

http://custom-wheels-blowers.centralblower.com/Asset/Determining-Static-Pressure.pdf

6" elbow is always 12' linear duct equivalent. there is no number for 4", so I estimated at 9'.

How do we solve for SP of ducting as a function of CFM? My calcs don't consider CFM until the fan curve. Do you have a good reference or calculator?

 

[schematix]

This is the document I was using. It is very long and has a lot of details. Between that and now being sick I haven't had the time to get through all of it, but it looks thorough.

http://web.fscj.edu/Mark.Bowman/handouts/ACCA Friction Rate Reference Chart.pdf

Note that for most fittings and pieces they gave an "EL" or equivalent length at a given velocity. There is a also a formula to calculate the EL if you have a different velocity.