Lampwork Etc.
 
AKDesign

LE Live Chat

Enter Live Chat

No users in chat


Jelveh Designs - Glass Beads Torched One-by-One

Beads of Courage


 

Go Back   Lampwork Etc. > Library > Safety

Safety -- Make sure you are safe!

Reply
 
Thread Tools
  #1  
Old 2015-09-25, 10:47am
x_phoenician's Avatar
x_phoenician x_phoenician is offline
Senior Member
 
Join Date: Aug 07, 2005
Location: Michigan
Posts: 2,135
Default Fan size based on hood size only? Makeup air under bench? Ventilation Help Needed

We're finally in the process of getting an exhaust system and electricity added to my new studio. I've been reading and reading and all the math involved is giving me a headache (literally).
What I'm understanding is that the only measurement that matters in deciding on what size fan to get is the opening of the hood...which we haven't had fabricated yet. Is this true?

The hvac man was here a couple days ago to look at the studio, which is 10x12 and give an estimate. He had no clue what we needed and said we have to figure out our exhaust requirements and then tell him what we need installed. He did mention installing a 800cfm high velocity fan with a controller that allows me to dial it up or down.

I like the design of Mary's studio in this thread http://www.lampworketc.com/forums/sh...d.php?t=265333
and that's what we're modeling mine after. I plan on having makeup air coming in from the side and up under that back of my bench. But now I'm worried that if I have air coming right up under my hood, that it won't pull enough contaminants away from my face area. I do have two small windows behind me on either side of the door so one or both could be cracked open. I just want to be able to work as long as possible during the cold months.

1. We need to decide on a hood size (30x30 is what we were thinking) but now I think I need an actual box to capture and funnel fumes. Originally I didn't want a fume hood because I was worried about it getting in my way, reaching to the sides, etc. Safety has to come first over convenience.

2. Then after we decide on the size for the extraction hood/box I have to multiply (say 2x3 box opening for example) by 125cfm? And that's it?

3. What about makeup air coming in from outside through 8 or 6 inch duct and under my bench and hood? Will I still need to have the back window open?

4. The exhaust is going straight up through the roof. I originally wanted the fan outside to help keep it as quiet as possible but the hvac man thought that was not the best idea (how to keep out bugs, critters, weather, etc.) He also mentioned having a cap on the end of the exhaust duct, like we have on our home roof where the water heater vents. I forgot what he called it (B pipe or something).

I appreciate any help. Thanks!
~Tracy
__________________
~*Tracy*~
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*

To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
Reply With Quote
  #2  
Old 2015-09-26, 2:47am
Speedslug's Avatar
Speedslug Speedslug is online now
Phill
 
Join Date: Mar 21, 2009
Location: Winnebago, MN
Posts: 1,956
Default

1) The cap on the top of the out side end will keep the rain from funneling straight in to you bench.

2) If you can control the make up air coming to the back of you bench that will allow you to adjust how much air comes over your shoulder and into your breathing space and since you are up in Michigan that can make a difference in how much expensive heated air $ goes to waste going outside.
If you can duct the make up air to your bench then you can at least put something over the opening to control the flow. More on this thought below.

3) I found a ten inch "blast gate" on Ebay for some $40 some 8 years back when I set up my system and I have it between my fan (inside) and the duct work going through the wall outside.



This closes the vent ducting when the fan is off to keep the heat from flowing outside when I am not running the fan.

4) The 125 cfm per square foot of hood area is the suggested minimum and the 800 you mentioned is only going to give you a hood of 3 feet by 2 feet.

Those numbers are for the air flow right at the face of the hood opening and would only apply if you are putting your hands through the face of the hood opening like a barley box with the torch actually inside the hood enclosure.

If you are going to mount the hood horizontally ( like you would over a standard kitchen cooking stove ) You need to in increase the flow rate by ( and I am guessing here, hopefully one of the experts can chime in here ) at least a factor of 4 if not a factor of 8 to ensure capture of the combustion fume sphere.



The equations the safety folks work with use the idea that the air is moving through an opening in the side of a big box and that you are sticking your arms and your nose into that opening in the box and are doing work through the side of the box. The box you're working in will contain the combustion fume sphere and the 125 cubic feet per minute of air flow through the opening is enough to prevent the fumes from getting into the room you are sitting in.

If you then lift this box over your head and turn it so the opening is parallel to the floor then you are going to need much greater air flow to keep the now uncontained combustion fume sphere from leaking out of the column of air moving toward the opening and into the room you are in.


A barley box is the best method of ensuing you capture all the fumes but working through a large hole in the side of a box is annoying.

When I put the knuckles of my hands together my elbows are about 3 feet apart. Add another 6 inches on either side for a little wriggle room and that totals 4 feet.

Resting my elbows on the bench with my hands straight up reaches at least 1 foot and a half. Add another 1 foot because I don't like bumping my head on the box I am working in and that works out to an opening in the side of the box of 4 feet by 2 and a half feet.

The math totals that out to a 10 square foot opening that you want to move 125 cfm through each square foot of and that math gives a minimum of 1250 cfm needed to keep the combustion fumes from leaking into the home I and my family live in.

The 3 foot by 2 foot opening that 800 cfm works for would be a lot like trying to work through the face of medium sized LCD TV.


Having the ability to vary the speed of the fan can also be a problem source.
The size of the working space is not going to vary at all and that would be the only real reason you would want to vary flow rate of the ventilation fan.

What you would want to adjust is the ratio of A) how much heated / air conditioned air you want to flow past your shoulder into your breathing zone and then in to the fan and B) how much make up air flows from the back of your bench to mix with the combustion fumes and then into the fan.

You could do that with another blast gate on the duct work of your make up air but you will need to set up some kind of incremental mechanism to get discrete control of how much air moves in that duct.


When I set up my blast gate to close off the fan ductwork from letting heated air flow up my chimney I used a pulley and wire rope with a magnet tied to the free end. I got the wire rope used for picture hanging from the hardware store and I used some of those magnetic business cards as landing pads to prevent the magnet from making marks on my painted hood.

I put the magnet on my metal hood at one spot to hold the gate open and I move it to another spot to let gravity close the gate. I only use the gate all the way open or all the way closed.

But a similar method could be used to control just how much make up air you allow to flow to the back of your bench.
__________________
So, What Do We Do Now? We continue to try to make a difference when and where we can. Because that's what we do.
Reply With Quote
  #3  
Old 2015-09-26, 12:54pm
x_phoenician's Avatar
x_phoenician x_phoenician is offline
Senior Member
 
Join Date: Aug 07, 2005
Location: Michigan
Posts: 2,135
Default

Thank you Phill.

I didn't plan on having the sides of the box go all the way to the edge of my bench so now I know the 800 cfm won't work. I like your magnetic pulley system, good idea.
__________________
~*Tracy*~
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*
To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
*

To view links or images in signatures your post count must be 5 or greater. You currently have 0 posts.
Reply With Quote
  #4  
Old 2015-09-27, 7:17am
Speedslug's Avatar
Speedslug Speedslug is online now
Phill
 
Join Date: Mar 21, 2009
Location: Winnebago, MN
Posts: 1,956
Default

Just be sure to always keep a little tension on the cable over the pulley.

Mine is up near the ceiling and behind the fan and my huge hood and is a real pain to get to when the cable gets caught out of its track and down in the crack between the pulley and it support cage.

Very annoying to bring in the 8 foot ladder and have to do the acrobatic act to get it unstuck.

In another decade I will be looking at 70 and I think the wifeunit is going to rescind my tight rope and high wire license.
__________________
So, What Do We Do Now? We continue to try to make a difference when and where we can. Because that's what we do.
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump




All times are GMT -7. The time now is 7:24am.


Powered by vBulletin® Version 3.7.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Your IP: 34.228.41.66