Need help designing ventilation system

[Melissa]

Hello Garage Journal!

I am having trouble designing / finding parts for my ventilation system....

My garage is about 14,750 cu ft. I would estimate about 4,750 cu ft of space is taken up by solids, leaving ~10,000 cu ft of air.

I have 2 wind powered roof turbines, each with a throat diameter of 18". I feel like mounting an exhaust fan in line with them would not work well due to them restricting the flow and creating turbulence. Therefore, I would like to remove the one in the rear of the garage, and replace it with a simple straight pipe that has a vent cap on it to keep rodents/rain from entering the system.

I was thinking something like this http://www.amazon.com/dp/B0085UZNKE/?tag=atomicindus08-20

If it came in 18", I would have ordered it already.....

The turbine is mounted to a metal "flange" that is 18" diameter at the top (mated to the turbine) and 22" x 22" at the bottom between the joists.

I then found this product...

http://www.amazon.com/dp/B000IJV7Y6/?tag=atomicindus08-20

For 3000 CFM, it seems like a great deal at $229 shipped. In the reviews, the shutters are made to seem of poor quality. I suppose I could fiberglass a hood that turns 90deg to place above it on the roof and integrate some mesh to keep the rain/rodents out...

What I don't like about that is that once I have it installed, I will be maxed at 3000 CFM. I will eventually be adding a spray booth that will require roughly 8000 cfm...

I am mostly interested in getting rid of the turbine and terminating it with an 18" pipe that extends above the garage and prevents rain. Then, at the 22 x 22 rectangle, I want some sort of Wye that I can build off of. Does anyone have any suggestions on how to get started with this?

 

[DEnd]

Why do you need such high cfm?

For the spray booth I would recommend you use a small cfm fan to positively pressurize the booth with filtered air, and then use a personal supplied air respirator system to get clean air for breathing while you are spraying in there. That will give you the cleanest air for breathing, and greatly reduce the amount of dust and dirt in the space as you are spraying.

Your use will determine how many cfm you will need, if you are going by ASHRAE recommendations then you need 1.5 cfm per sqft of floor area for auto repair rooms. That is a really high cfm rate, and due to this I would recommend separating the repair area from the storage area if you are using it as a automotive hobby garage. You also want to have the exhaust pull air from the floor area of the shop as most of the pollutants are heavier than air.

If you are using it for woodwork, then ASHRAE recommends a minimum of .5 cfm per sqft. If you are using a dust collection system that evacuates the dust and air outside the building (such as a vacuum system where the bags and equipment are in an outside shed) then those cfm can be used in the calculation as well.

Regardless of the use if it is going for professional use or if you will have employees working in there it is much better to find a licensed architect or engineer with appropriate experience to design your ventilation system. Not using the appropriate professional in this case is asking for trouble.

 

[pseudorealityx]

Those ASHRAE numbers are just the normal ventilation requirements for those types of spaces. For a specific fume hood/spray booth/whatever, that should be determined in addition to those numbers, based on the manufacturer's data, or if designing your own, using typical air change/flow velocity/etc to determine the right airflow.

Also... you don't provide a location. Either 3000 or 8000 cfm... unless you live in a perfect climate, that sounds like a potential problem.

 

[Chris705]

The vent cap you link can be found in 18" at a commercial supply house that sells ductwork. I would recommend a larger thru the wall fan with louvers also available at the HVAC supply house. These are not cheap but you want to move a large among of air not sure going thru the roof turbine is going to accomplish what you want it to.

 

[Melissa]

I live in a Mediterranean climate. All of my tools and work stations are on wheels so my space can be reconfigured based on project. I do more than just work on cars, so I like having everything modular and re-configurable.

I already have a dust collector w/ 1550 cfm/ 2 micron bag, and that is attached to my table saw. I cut a lot of MDF which produces very fine dust and I feel like that floats around in the air and would be evacuated fairly easy with a powered roof turbine without having to have the inlets extend too far down toward the floor. I'm also concerned with welding fumes and other things so I would like to make something like this

http://www.grainger.com/product/2DB...ci_sku=2DBX2&gclid=CJPRsLCIusICFRRcfgodyKoAzA

Has anyone seen or heard of someone making a nice one for substantially cheaper than this? Link would be amazing. I have the end fitting down, I just need to design the arm.

Your combined advice is very appreciated and I think I'm going to partition off storage areas completely, as well as do a better job of sealing off my office from the rest of the shop. I'll visit a local HVAC supply store to find the appropriate materials for the roof vent and Wye. I am the only person who works here (no employees) so this is strictly for my personal safety, although I'd like to comply with the standards because they are there for a reason.

I am going to make a separate thread regarding the DIY fume extractor hood here http://www.garagejournal.com/forum/showthread.php?p=4448437. With a roof turbine, my dust collector, and a maneuverable hood, I think I will be 90% of the way there.

 

[Melissa]

For the spray booth I would recommend you use a small cfm fan to positively pressurize the booth with filtered air, and then use a personal supplied air respirator system to get clean air for breathing while you are spraying in there. That will give you the cleanest air for breathing, and greatly reduce the amount of dust and dirt in the space as you are spraying.
.

This is exactly my plan, and I have already made a direct air supply respirator. I will post up pics when I have a chance to see if it is up to snuff.

 

[DEnd]

You said you are in a Mediterranean climate, will you be heating and cooling the space at all? If you don't need to heat, cool or dehumidify the space you are probably just as well off to get a gable end fan or two (as well as using your fume extraction ideas). If you need to heat and cool the space however that won't really work well.