CraftWEB Hot Glass Talk  

Go Back   CraftWEB Hot Glass Talk > Hot Glass > General Hot Glass Discussion

Reply
 
Thread Tools Display Modes
  #1  
Old 11-11-2017, 11:45 AM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Naturally vented furnace

Iím finally moving to a bigger space. Itís time to build a gas furnace and leave the wire melter behind. In planning a new shop, Iím considering putting together some sort of draft flue for venting the furnace with the natural stack effect. It seems there would be so many benefits to having a naturally vented furnace in addition to having the typical fan vented hood over the equipment. Itíl take some creativity but I think I can plan a mechanically sound system.

Im sure someone has experience with this but I canít recall ever seeing it in any studios. Anyone have any input?
Reply With Quote
  #2  
Old 11-11-2017, 04:39 PM
Jordan Kube Jordan Kube is offline
?
 
Join Date: Aug 2003
Location: Seattle, WA
Posts: 1,505
Jordan Kube is on a distinguished road
Unless you have the ability to build a very tall flue you will want to go with fans.
__________________
WWUD? Think for yourself.
Reply With Quote
  #3  
Old 11-11-2017, 06:39 PM
Eben Horton Eben Horton is offline
Registered User
 
Join Date: Apr 2002
Location: Wakefield, RI
Posts: 3,944
Eben Horton is on a distinguished road
The longer the flue, the more the pull and the more it will cost to run. Stick a funnel shape of metal above the normal sized furnace flue and it will draw room air up the vent along with what ever exhaust was naturally going to vent out of the furnace. Does that make sense ?
Reply With Quote
  #4  
Old 11-11-2017, 06:41 PM
Rich Samuel's Avatar
Rich Samuel Rich Samuel is offline
Registered User
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 2,249
Rich Samuel is on a distinguished road
A giant vertical venturi, right?
Reply With Quote
  #5  
Old 11-11-2017, 07:06 PM
Steven O'Day Steven O'Day is offline
Registered User
 
Join Date: Jun 2002
Location: portland oregon
Posts: 264
Steven O'Day is on a distinguished road
You could try a small version of those vents they have on glass factory roofs, I believe they are called Robertson ventilators. They look like a horizontal venturi.
Reply With Quote
  #6  
Old 11-11-2017, 08:51 PM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Ohh thatsss what they're called! Yea Robertson ventilators are a really cool concept. Not really what I was thinking though.

Let me be more specific about what I have in mind. Eben, you pretty much nailed it. Imagine a furnace with a recuperator stack under a normal x' by x' vent hood. Just Over the recuperator would be a small draft hood and a length of 7" chimney pipe piercing through the vent hood (the draft hood is the little funnel thing and the vent hood being the big thing over the funrace and ghole). The chimney would then continue rising up through the building roof and terminate. Following building codes for chimeys and wood burning stoves and maybe adding a few inches to the clearances should be safe. I figured 7" pipe being that is a typical size vent for 180k-300k btu boilers and furnaces, and should be generous for a recuperated 150# or 200# pot furnace.

It would be nice to have this type of setup during the winter. Just getting rid of the exhaust and keeping the furnace heat in the studio. No fan power to pay for. One less mechanical thing to worry about, especially while idling the furnace for a week of coldworking or a show or something. Then while blowing, the fan for the vent hood can be turned on and the furnace exhaust would spill from the draft hood and leave through the fan.

Either this would be a totally superfluous addition to a studio or there are studios out there already doing this. I'm scratching my head.
Reply With Quote
  #7  
Old 11-12-2017, 09:36 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 19,309
Pete VanderLaan is on a distinguished road
Having tried it years ago, it was hopelessly inadequate on a 250 pot furnace. The smokey newspaper test at the edge of the hood will tell you everything. It's OK for clear melts but not any more than that
Think hot shopinsulate your hood.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #8  
Old 11-12-2017, 11:32 AM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Pete, I'd really like to hear more about your experiment. Are you talking about the big ventilation hood over your furnace and ghole or a small chimney draft hood above the flue? How tall was the piping?
Reply With Quote
  #9  
Old 11-12-2017, 04:58 PM
Josh Bernbaum Josh Bernbaum is offline
Registered User
 
Join Date: Feb 2009
Location: Brattleboro, VT
Posts: 494
Josh Bernbaum is on a distinguished road
So Marc, all those phosphates you've done were in a wire-melter? Wow.

I've been liking this in-line small "flue vent" fan I put in the (I think 7" or so) vertical pipe I have above the flue on my recuperated gas furnace. The motor is offset outside the piping but the fan parts are not, but it's still rated for a couple hundred degrees F I think. The flanged piping is about 2-3 inches above the top of where the gases exit the recuperator stack, and then that in-line motor is a couple feet above that. It passes Pete's smoke test and seemed to have passed my fluorine tests and it draws very little wattage. I can send you some pics if you'd like to consider the idea further.
__________________
www.jmbglass.com
instagram.com/joshbernbaum_glass
Reply With Quote
  #10  
Old 11-12-2017, 05:34 PM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Thanks Josh. Yes but my wire melter has a tiny air/oxy flame in the headspace for when i'm cooking or blowing. Anyway, a good phosphate recipe needs no hotter cook temps than a clear. In my case thats 2250.

That exhaust setup sounds really cool. Did you design it? How do you like the benefits of it? Yes I'd very much appreciate a pic or two of that.
Reply With Quote
  #11  
Old 11-12-2017, 05:42 PM
Peter Bowles Peter Bowles is offline
Registered User
 
Join Date: Sep 2002
Location: Breadalbane, Tasmania
Posts: 597
Peter Bowles is on a distinguished road
If you are using forced air, its not such an issue, but if you are naturally aspirating your furnace you might run into issues with changing barometric pressure if the flue is directly connected to the stack.
Reply With Quote
  #12  
Old 11-12-2017, 08:21 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 19,309
Pete VanderLaan is on a distinguished road
When I built my first indoor furnaces, I made way too large a hood and it was just sheet metal with duct tape on the joint and it was essentially a giant radiator. It had a 16 inch pipe right over the top of the furnace going through the roof but there was a gloryhole to it's left. It had a natural venturi top piece and the whole thing was about fifteen feet tall.

That shop was really hot.

At that time, I wasn't doing such things as smoke tests but all it essentially is is a damp piece of paper, lit that is held right at the edge of the hood. If the smoke gets sucked into the hood, you're good to go. If it curls up outside the hood anywhere along the line, you're not only heating the building, you're exhausting the hood contents into the room as well.

When we built the second shop, I abandoned the venturi and had six 3500 CFM fans mounted in the hood at the top of the pitch. I had three additional 3500 fans in the batch room. Each fan had a separate switch so it could be ramped up or down. It exhausted about 30,000 CFM and that was an air change every 20 seconds. If you have less than an air change every two minutes based on the cubic footage of the room, expect it to be hot. People from the first color class seemed to think it was good and It certainly passed the smoke test, or sucking just about anything into the hood. This time, the hood was made of metal but had one inch HVAC board attached to that metal so it was actually insulated.
The third shop, when we moved to New Hampshire has a smaller hood, still insulated but less exhaust. I recognize now that if you build the hood tightly around the units to be exhausted, you can use far less exhaust power.

These days I have much smaller tooling and my days in production are done. After working all these hoods over decades, I would not try to use a venturi hood. This last shop, with the smaller hood runs about two to three degrees hotter indoors than out. I bring the gloryhole out from under the hood in winter just to heat the joint.

I rarely see a shop with an insulated hood. Indeed it costs more to build but the comfort level is really nice.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #13  
Old 11-12-2017, 08:26 PM
Josh Bernbaum Josh Bernbaum is offline
Registered User
 
Join Date: Feb 2009
Location: Brattleboro, VT
Posts: 494
Josh Bernbaum is on a distinguished road
Here ya go Marc. Disregard the other bigger duct in the background (that's for a separate small hood capturing fumes over door) but you can see the top of the flue/recuperator in the foreground in the first pic, a couple inch gap, then that flange that starts the ducting up for a few feet then turns horizontal to go out side of building. I was wrong we mounted that fan closer to the wall. It may or may not matter how far it is from the intake. This way at least it keeps as cool as possible but honestly the exhaust gasses aren't that hot after going through a good recuperation system. I think this is the fan info:
http://www.tjernlund.com/Tjernlund_8506000.pdf Sorry, just noticed the pics are sideways after posting them here..
Attached Images
File Type: jpg IMG_7916.jpg (25.0 KB, 23 views)
File Type: jpg IMG_7918.jpg (22.9 KB, 18 views)
__________________
www.jmbglass.com
instagram.com/joshbernbaum_glass

Last edited by Josh Bernbaum; 11-12-2017 at 08:29 PM.
Reply With Quote
  #14  
Old 11-12-2017, 08:28 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 19,309
Pete VanderLaan is on a distinguished road
toxic melts and recuperation can be really problematic. It's fine on a clear furnace.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #15  
Old 11-12-2017, 08:30 PM
Josh Bernbaum Josh Bernbaum is offline
Registered User
 
Join Date: Feb 2009
Location: Brattleboro, VT
Posts: 494
Josh Bernbaum is on a distinguished road
Quote:
Originally Posted by Pete VanderLaan View Post
toxic melts and recuperation can be really problematic.
OK I'll bite. How so..?
__________________
www.jmbglass.com
instagram.com/joshbernbaum_glass
Reply With Quote
  #16  
Old 11-12-2017, 09:14 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 19,309
Pete VanderLaan is on a distinguished road
well, that preheated air got heated in the furnace atmosphere and has a way of settling on the recuperator to the point where you want to be careful when time comes to clean it which will come.
I did not run really efficient recuperators in Santa Fe so they actually didn't clog up but I've seen the ones that can run 700F air and they do eventually clog. Sometimes faster than eventually. Just be cautious.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #17  
Old 11-12-2017, 10:02 PM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Ahh yes Peter, I see what you're saying. I'm planning on using forced combustion air and a draft hood gap.

Pete, thanks for the extra info. I just found this nifty calculator online http://chuck-wright.com/calculators/stack_effect.html . Punching in the numbers, with a 140f underhood temp (that sound right?) and 70f outdoor temp, a 16" stack 15' tall would vent about 578 cfm. Not terrible but when you divide that figure by the area of the hood opening, I wouldn't be surprised if it didn't pull smoke from a couple feet away. That calculator looks like a sterile equation though, not taking into account real world factors like the benefits of wind on a venturi cap or the drawbacks of heat loss in the stack. Now 30,000 cfm sounds like a goddamn wind tunnel! I don't think the neighbors would let me get away with that haha.

I'm very interested in recuperation issues too but I'll save that for another thread. Oh and I'm definitely sold on the insulated hood idea. Sheetrock, really? Eh, you da fireman.

Thanks Josh! That looks like a really cool setup and a nice little fan. The specs on the unit really help me with sizing a draft system too. According to the draft calculator, a 15' rise of 7" pipe would have similar venting capability (218 cfm) as long as the flue gas is above 500f.
Reply With Quote
  #18  
Old 11-13-2017, 10:03 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 19,309
Pete VanderLaan is on a distinguished road
Don't neglect adding in the forced air from the glory hole or the heat generated from a pipe warmer. It's deceptive. If you indeed are using forced air for combustion, it's creating a positive pressure in the furnace , which along with the expansion gasses of combustion ( either 9 or 27 to one, I forget) is creating more pressure and velocity than you may realize. So, coupling that up with what is essentially a static venturi draft from the stack, and if it uses one of those wind driven exhausts, You are likely to be disappointed in how well it works, or if it really satisfies you at all.

Early hoods I had were freestanding and again, too large. The last two are lean to structures against a wall and have 24 inch diameter fans built into the wall going outside, so there's no stack at all. Each fan pulls about 3500 CFM and in the current shop, given the tiny nature of the hood, that works quite well. If the hood was large, it wouldn't work. The HVAC board is critical to comfort but keep in mind the resin in it is flammable so it needs sheetrock on the hotface side and if you don't like dust from the studio, having rock on the outside is far easier to clean, which you probably won't do.
The penetration of the wall was my biggest issue and I am a former paid firechief and the building is made of white Pine we milled from the forest, so in building that particular interface, I really went overboard on using steel and dead air in triple forms to keep it highly fire resistant. The fans live in a welded angle iron frame which is isolated thermally from the wooden walls as well. It was a job figuring out how to do that. I now have to live with propane and it's a scary gas for me. I simply refused to install a conventional safety system given the cost and devised one of my own design which has repeatedly worked perfectly yet only cost 400 dollars. I also doubt it would be acceptable to an inspector unless they were smart. There is no building code where I live. They brought the propane tank one day, we buried it, they filled it and left.

The local motto should be "every man's home is his own crematorium"

But that draft hood is gonna give you trouble.
************


Quote:
Originally Posted by Marc Carmen View Post
Ahh yes Peter, I see what you're saying. I'm planning on using forced combustion air and a draft hood gap.

Pete, thanks for the extra info. I just found this nifty calculator online http://chuck-wright.com/calculators/stack_effect.html . Punching in the numbers, with a 140f underhood temp (that sound right?) and 70f outdoor temp, a 16" stack 15' tall would vent about 578 cfm. Not terrible but when you divide that figure by the area of the hood opening, I wouldn't be surprised if it didn't pull smoke from a couple feet away. That calculator looks like a sterile equation though, not taking into account real world factors like the benefits of wind on a venturi cap or the drawbacks of heat loss in the stack. Now 30,000 cfm sounds like a goddamn wind tunnel! I don't think the neighbors would let me get away with that haha.

I'm very interested in recuperation issues too but I'll save that for another thread. Oh and I'm definitely sold on the insulated hood idea. Sheetrock, really? Eh, you da fireman.

Thanks Josh! That looks like a really cool setup and a nice little fan. The specs on the unit really help me with sizing a draft system too. According to the draft calculator, a 15' rise of 7" pipe would have similar venting capability (218 cfm) as long as the flue gas is above 500f.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #19  
Old 11-13-2017, 04:36 PM
Marc Carmen Marc Carmen is offline
Registered User
 
Join Date: Jul 2015
Location: New Jersey
Posts: 66
Marc Carmen is on a distinguished road
Pete I agree with everything you're saying. I don't think anything short of an old-timey brick stack could get rid rid of the exhaust and heat of an entire shop's equipment. What I have in mind is something like what Josh has pictured except with a stack vent instead of a power vent. somthing that just takes care of the furnace exhaust. This would be in addition to a big hood with power fan over all of the equipment. I'd imagine only needing to turn on the big power fan while blowing or charging, and then let the little stack vent take care of the furnace exhaust overnight or when the furnace is just idling.

So you're using sheetrock on the hotface of the hood? I guess the temps don't get hot enough to mess with the paper face? And when you say HVAC board, you mean the fiberglass board kind of stuff? The custom iron frame for the fan sounds like a great idea for going through wood walls. Is it just an air gap between the fan and the frame or did you insulate it?

Can you be more specific about this safety system? I know exactly what you mean about smart inspectors. I was a plumber before glass. Unique or creative solutions would sometimes offend dumber inspectors. I'm working with very strict plumbing and building codes here in NJ so I may start a thread about staying on the right side of all that.

I appreciate the good info
Reply With Quote
Reply


Thread Tools
Display Modes

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 Off
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 02:31 AM.


All published comments within these message boards are the opinions of its contributor and does not represent
the opinion(s) of the owner(s) of this website. Please see the Terms of Use file for more details.

Books to Help Artists Avoid Online Scams: Top 10 Email Scams | Social Media Scams

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
© CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.