melamine fume hood build more space? or better air flow?

[BGDOCK]

Using those Furnco”s is a good idea , back to the drawing board

 

[skinny]

I think where your horizontal airflow intersects your vertical airflow it will cause back pressure issues. I would angle the horizontal up at a 45 a few feet past where it picks up the hood air and insert a second TY a few feet above where the vertical TY picks up the hood air. This way you would have both airstreams well on their path and not interfere with each other.

You realize you have to compress the airflow from the blower and allow it to decompress and draw air from the hood just as it passes the hood opening. Your sketch does not show that compressing.

Hey man thanks for your input Ive got two new drawings to account for your suggestions I'm sorry they are so bad but what do you think of this? I'm thinking of just using rigid schedule 40 for all of the ducting up to the ceiling and then converting to a PVC dryer vent type ducting to the roof which will be a PVC roof exhaust flashing

 

[4metals]

As long as you exit the roof at the same diameter your riser to the roof is. don't narrow it down as it will cause back pressure. Also consider drawing in outside air for your fans, the smaller the room is the more important it becomes. If the fan is 100% room air it competes with the air you draw from the venturi and lowers efficiency. Outside air is nice, especially in winter when you have to heat all of the air in your shop. The air pulled through the fan is exhausted and the only air you have to heat (or air condition) is the extra air the venturi picks up from the hood.

 

[4metals]

I made long tapers for the venturi by cutting up traffic cones so it sat snug in the pipe close to the fan and opening the discharge end to about 3" for an 8" pipe. That made a smooth taper to compress the air. (It also pissed off my son because I stole one of his soccer goal cones.)

 

[skinny]

As long as you exit the roof at the same diameter your riser to the roof is. don't narrow it down as it will cause back pressure. Also consider drawing in outside air for your fans, the smaller the room is the more important it becomes. If the fan is 100% room air it competes with the air you draw from the venturi and lowers efficiency. Outside air is nice, especially in winter when you have to heat all of the air in your shop. The air pulled through the fan is exhausted and the only air you have to heat (or air condition) is the extra air the venturi picks up from the hood.

Good points I do plan to go 8 inch all the way to the roof pretty much a straight shot. As for the intakes I positioned my fume hood about 4 feet from the opening of my garage door I live in Texas so it's hot in the garage about 8 months out of the year I have a small shop swamp cooler I use to move air around and cool it off. I'm also a night owl so I'll be doing most of my work after my kids have gone to bed overnight when it's cooler as well I'll include some pictures for reference but Ill probably mount the 8"blower on the wall where my whiteboard it and I'll have to relocate that but it would put the blower 2 feet from the garage door entrance hopefully giving it access to plenty of air as long as the garage is open. The 6 inch booster blower though I'm not sure if I can rig it up the same it will be piped through my workbench closer to the ground but still suspended pulling air up from ground level. I included a second design I just came up with both vents on the hood being on the top instead of having one on the side can you tell me your opinion on which you would go with? If you had my hood and garage how would you vent it differently than what I'm trying to do to accomplish what I'm wanting to?

 

[4metals]

If you are always going to work with the door open the outside venting of the air intake is moot, that only matters in the winter. From the press about Texas power outages in winter storms I have changed my thinking about how cold Texas can get. Especially north Texas.

As far as 1 venturi or two, I have no experience using 2 in the same hood and I always vented from the top center. One thing nice about 2 fans is if you have a lot of reactions in process you can shut off the larger fan if the reactions are proceeding slowly and save on electricity.

 

[skinny]

cool, yeah i live in west texas in the oil field desert although we did get hit with that ice storm that definitly wasnt normal it does get cold but not too cold i couldnt be in my work area with a good hoodie. thats what i was thinking too with two fans both are controllable so i can turn them up or down as needed turn one or both off. ill also be building a gas scrubber this weekend thatll be in use at the same time i just want to make sure i get a good vacuum at the front of the hood so if im working with that right sash up i still wont worry about anything escaping. i guess the best i can do is experiment with the parimeters youve given me and see what works i just dont want to be poking a bunch of holes in my new hood and failing haha

 

[skinny]

If you are always going to work with the door open the outside venting of the air intake is moot, that only matters in the winter. From the press about Texas power outages in winter storms I have changed my thinking about how cold Texas can get. Especially north Texas.

As far as 1 venturi or two, I have no experience using 2 in the same hood and I always vented from the top center. One thing nice about 2 fans is if you have a lot of reactions in process you can shut off the larger fan if the reactions are proceeding slowly and save on electricity.

 

[4metals]

I see a sheet metal tee in the photo. Just hoping that isn't for the acid exhaust!

 

[skinny]

I see a sheet metal tee in the photo. Just hoping that isn't for the acid exhaust!

hahaha no its not it was attached to the blower to the blower i own no all pipe will be pvc if i can help it itll look a bit industrial but thats what this calls for
i wont be using tees either im gonna try to use as many 45s as possible like you said the sir flow has to be at the right velocity to work and a t or 90 will kill it

 

[Martijn]

I used an outdoor light. Just replaced it after ten years. I use one with a cable gland that can be tightened so there won't get any gas inside.

 

[BGDOCK]

That stained plywood and curved plexiglass is a nice touch it’s kinda art deco .

 

[4metals]

I used an outdoor light. Just replaced it after ten years. I use one with a cable gland that can be tightened so there won't get any gas inside.

The hood looks like it comes from an old Frankenstein era laboratory! It could go into Hoke's book as a centerfold.

 

[Shark]

Yep, I like that curved hood as well. A Lot!

 

[snoman701]

Using those Furnco”s is a good idea , back to the drawing board

Just know that they are the ones that work. I spent a good amount of time researching it. There are different ones for different types of ends. From PVC to Black pipe to concrete...and they all have different inner diameters that they snug down on. Those ones will get you over the lip of the blower, so you can tighten the hose clamp down on the body.

 

[BGDOCK]

I came up through the HVAC trade spending some time in the sheet metal shop. Went with what was familiar to me when you mentioned the Furnco’s , I was like why didn’t I think of that