Ducted Exhaust Fan

[cory58]

I'm hoping to get some advice from the GJ experts regarding an idea I have for an exhaust fan in my new garage. I've found several exhaust fan threads, but none that address my specific question.

My garage is a 30x50 metal building with 2 large roll-up doors. Walls are 13' and the peak is about 18'. I just had A/C installed, but would also like to exhaust the hot air out of the peak in the summer to keep the building temperature reasonable when the A/C is not running.

Here is the challenge: I don't want to mount the fan on the end of the building that has the peak or cut a hole in the roof. Due to the structure of the building, the max mounting height on the side walls is approx 10'. Since I'm trying to exhaust the hottest air from the peak of the building and the fan (or the output duct from the fan) can only be at 10', I was thinking that some sort of ducted fan would be the best solution. I'm thinking there are 3 options and I am ok with any of them.

1. Fan mounted to the exterior wall with a supply duct run up to the peak. This is what I envisioned, but can't find options made for use with a supply duct.

https://www.globalindustrial.com/p/hvac/exhaust-fans/exhaust-and-supply/tpi-exhaust-fan-10-in-with-shutter-3-speed?trackType=3&trackPrimKey=0&trackCatKey=4449&webCatKey=5463&presentType=3

2. An inline fan like this, but the options I'm finding for this type of fan all seem to be lower CFM for bathroom exhaust or air movement in grow houses.

https://www.globalindustrial.com/g/hvac/exhaust-fans/in-line-duct-fans/in-line-range-hood-exhaust-fans?trackType=3&trackPrimKey=0&trackCatKey=4449&webCatKey=5463&presentType=3?ref=cat/b/inlinefans

3. I haven't thought much about this option, but a fan could be mounted up in the peak with the output ducted down to a hole in the side wall.

Sorry for the long post. I would appreciate any feedback on my ideas. I ran them by the tech who installed the A/C and he seemed to think I would not get the desired result unless I take the traditional route of exhaust fan and corresponding intake vent mounted in opposite ends of the peak wall, which is not an option.

Am I going to waste time and money with any sort of ducted option? If not, what would be the best solution?

Knowing that a building like mine (with roll-up doors) is not even close to air tight, do I need a corresponding intake to get good results?

Thank you!

Cory

 

[Kaizen]

Why don’t you want to cut into the sidewall or roof? I don’t like your idea as it’s going to bring hot air down into the ac space. Even if you insulate it you introduce leak points.
I’d consider either windows or louvers at each peak with one fan inside so it can’t be seen. Yea your garage leaks but a fan with no supply will take from wherever and work way to hard. It could be sucking up the ac.


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[Kaizen]

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[75gmck25]

One simple solution would be a full ridge vent, along with a couple of ceiling fans that are set to pull the hot air up. Of course that assumes you have vented soffits, or a window or door open on the lower part of the wall that will let the makeup air flow in. It would be a great solution on mild days when you have the large garage doors open.

The only downside to the open ridge vent is that the vents will also be open in the winter, so you will watch all your heat go out the roof.

The other consideration for your location is that usually the humidity is more oppressive than the heat, and air flow does not make humidity feel that much better.

Bruce

 

[Vultee]

HVAC Pro here - first post... your shop has approx 20,000 cubic feet of interior volume. So keep that in mind as you select a fan. Prop fans move greater volume with lower power consumption but don't handle pressure well, that's where a squirrel cage blower works best. I've installed a high sidewall prop type exhaust with automatic louvers similar to your link, only much larger. It was to ventilate a comp shingle manufacturer storage warehouse. Worked well.

But I'm wondering if you might need more CFM? With only 1,000 CFM working on low speed it's going to take 20 minutes for an air change - so not much movement. Would a larger fan sidewall fan fit in your install location? Running a bigger fan at lower speed gives less noise signature. Check db or sones if given (usually not for industrial stuff). Typical A/C condensing unit fan is 1/3 hp, moves about 2 or 3,000 CFM. Might be able to repurpose one of those but it won't like blowing open the louvers.

 

[metlmunchr]

Not sure why this would have been moved to electrical.......

Propeller fans like the one you linked won't develop enough static pressure to handle any ductwork on either side. You'd have to use something like a spray booth fan that has a tubular housing and blades with a form designed to develop pressure. These are typically called tubeaxial fans. You can easily spend $1500 on a fan like this once you have the fan, motor, drive pulleys, and belts. They're built for specific uses and have much heavier construction than any sort of normal residential ventilation equipment, hence the relatively high cost.

HVAC contractors are changing out old systems on a daily basis and scrapping the old equipment. A 5 ton air handler from a straight cooling or heat pump system will move about 2000 cfm @ 1/2" external static pressure. I'd check with some local contractors and see what they'd want for a used air handler from a changeout. $50 is way more than it would be worth as scrap. Strip out the cooling coil and you have a cased centrifugal fan suitable for attaching duct. Hang it at the peak of the roof and run the duct to wherever you want it to discharge. Probably best to hang it near one end of the building and install a louver with gravity damper for the makeup air near the opposite end to minimize the chance of air short circuiting directly from the inlet to the fan. You would need a louver at the inlet to prevent sucking in water when its raining.

Lots of ways to do this, but that's the cheapest and simplest way I can think of to avoid roof or end wall openings.

 

[cory58]

I also don't understand why a ventilation thread got moved to the electrical section, but many thanks for the great responses. Once again the willingness of people on GJ to share their expertise has saved me time and money.

Cory