Garage ventilation

manicrodder

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It is so humid here I don’t think that would work. And I don’t really want more moisture in the space. What I want to avoid is the hot, stagnant air, that gets moisture coming up from the gravel floor after it rains and the ground is wet. It just makes for a nasty hot environment, much less comfortable than when you step outside.
But you can leave the pump off and get a lot of ventilation.
 

JHZR2

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The smaller ones move 1000 cfm.
I have an 1800 com box fan right now. Even if I put it in the door blowing inwards, I don’t get what I consider to be a good air exchange. In most of the 20x40 first bay that is my workshop, even with the fan blowing, the air is nasty hot, and on these heat wave high humidity days where it rains at night and the ground is damp, it’s more humid than outside as well.
 
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I have a 10 bay garage, each bay is partitioned from the next, and each bay has a sliding barn door to keep the elements out. They are not sealed. They have combination gravel and cement floors.

The entire building has a gable roof, around 120’ total length. All the bays are partitioned so there really isn’t a way to mix air or flow from one to the next. Id like to keep some airflow in my two adjacent bays where I have a little workshop (and there is the ability for some cross-flow). It is terribly hot in there in the recent heat wave, no air mixing, just stagnant, even with a box fan blowing across the space. Im thinking some sort of small exhaust fan like is used in a Bathroom, just to force more exterior air all the time. I tried a 4” booster fan, it was way too weak. I’m thinking some bathroom fan as it’s considered an originating air handling device, not a booster, and may be able to keep its cams with more drop over a longer length.

I don’t want to spend a ton, but I do want to get some airflow since the gravel tends to allow water vapor to rise up through. I’d prefer not to put any fan on the roof. Any suggestions thst aren’t too big or small?
Pic?

Thinking.. if bay doors were kept closed and air was circulated inside.

Warehouses do get stupidly hot; I am in the AC as much as possible during day, I consider this a luxury and am thankful. Trying to circulate as much cool air as you can will help.

Garage that services my vehicles has doors on the front and back, kept open, three lifts and one in the back, so four. I think they are going for a crosswind
 
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If you haven't already, get some metallized insulation stapled to the underside of the roof. There's a type that reflects longwave infrared.
 
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Garage that services my vehicles has doors on the front and back, kept open, three lifts and one in the back, so four. I think they are going for a crosswind
I've seen many auto repair shops like that, obviously those that aren't air-conditioned (I suspect that's rare - A/C'd, that is). It seems to work quite well or well enough, I mean.
 
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I would try to seal off your workarea decently even if with plastic sheeting or similar.. and run a mini split..
alternative would be some roof mount solar powered(or electric) fans.
 

JTK

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Can you run a gable fan at the peak of one end of the building and a fresh air in louver at the other end? It would have to be a large fan, or several.
 
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I've seen many auto repair shops like that, obviously those that aren't air-conditioned (I suspect that's rare - A/C'd, that is). It seems to work quite well or well enough, I mean.
The movement of the air is key!

It can feel very good, yes
 

UncleDave

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If you cant mix in cool air then a high diameter ceiling fan is how Id cool, these are very quiet while moving a ton of air.

a swamper in NJ won't work a high% of time.

something like this, or as large as you can afford to go, being inside you can get by with a lower end uni.

 
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UncleDave

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If the roof is in direct sun when you are inside, Paint the ceiling white to reduce emissivity of the likely darkened lumber, or staple some reflectix or smartshield radiant barrier to it.

I much prefer the 5mm SmartShield over mylar coated double bubble 'reflectix' , for durability, and ease of installation, though radiant barrier efficacy is very close. The SS will however block more Wifi and its aluminum skin is electrically conductive where the reflectix is not. SS has a version with one white side, and one silver, which makes for a nicer interior feeling, but is slightly less effective at reducing radiant heat than the dual silver sided version.

Your box fan pushing in outside air, will never push out the hottest air above the level of door openings, and a ceiling fan up there mixing the hottest air with cooler from below, is not as effective as if that hot air were exhausted from within, and cooler air allowed in to replace it.

I recently took some large uncreased cardboard boxes from the neighbors as they dragged towards the recycle bins, and made a 20x20" 5 foot long rectangular duct to fit tightly on the box fan. The open end of the duct is withing a foot of the ceiling, sucking the hottest air from there and exhausting it out the opened door and up off to the side with prevailing wind direction, as I too did not want to cut a hole in the roof.

I turn the fan on and put one hand in front of its outflow and it is significantly hotter than the air rushing in at my feet and whole workshop quickly cools to near ambient, an the earlier in the day I start the box fan exhausting the ceiling, the more effective as the ceiling timbers are not allowed to heat as much and radiate heat downward, and preventing that additional heat from heating the contents within nearly as much.

I have not yet lined my ceiling with radiant barrier, but did paint my southwest facing walls white, which greatly reduced the feeling of looking into a blast furnace in the afternoon. I can feel radiated heat from ceiling too, and while radiant barrier would be better than white paint and white paint better than dark old wood, for now I have a secondary ceiling over workbench, made from lightweight lumber scraps, that also holds my LED light bars over my workbench, which blocks ceiling radiant heat from reaching me standing at workbench, and helping to keep all contents below cooler as well.

The 20x20 box fan duct scavenging the hottest air from the ceiling and exhausting it outside, is extremely effective in allowing the workspace to remain pleasant and likely while I will not purchase and install the radiant barrier on the ceiling..

My sheepdog chooses the workshop floor in front of door, whenever it is hottest, and this specific spot is south facing with only a tarp preventing sunlight from hitting the concrete floor and area in front of it.
 

JHZR2

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I took a step in the generally right direction.

I was experimenting with cheap 4” duct booster fans from Amazon. That was folly - it didn’t flow worth a darn. I then tried the cheapest Broan-NuTone vent fan from HD on a whim; they are designed for pushing air from a space, through a duct, to the weather. $15 or so and made in the USA. Put in a horizontal support on my rafters at the very top, and mounted the fan. Put 4” duct to one of the between rafter spots where I saw some daylight.

While the 4” booster fan, rated at 100CFM could barely move any air in a meaningful,way, the $15 vent fan rated at 50CFM moves… 50CFM. Or enough to make a difference.

If I assume that the 20x20 workshop space is on average, 10 ft high, it’s 4000ft3. 50CFM seems like nothing. It would only exchange the air every 80min. But that seems pretty good. It did enough to feel different, feel a much better comfort level after running maybe 30 mins. Even without the exhaust really getting out to the weather as effectively as it should. Just mixing the hottest air in there by forcing it through the fan makes a major difference.

No idea how well a fan like this will work in near continuous duty. I might put it on a timer. But for $15 I can afford to replace them I guess. Perhaps for my workshop area I’ll get a higher rated one, but other bays this is good enough… I think. The higher cfm fans are all designed for quiet and are more expensive.

Will need to see how well it does over another few hot days, but this is easy enough to implement. Some guidance talked about 1cfm per square foot of floor space, or the need to exchange all air many times per hour. That seems for now to be overkill. Knock on wood this is all it takes to just get some fresh air blended in here.
 
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CFM ratings are not actually done by measuring the volume of air moved in 60 seconds, they take the velocity of the air exiting, and multiply it times the diameter of the aperture. There is NO restriction to airflow in this test, and when there is actually restriction, the actual amount of air moved can be a tiny fraction of that CFM claim.

Even if there is no restriction to flow in a certain application, most fans have hotspots of flow exiting the fan. No doubt the anemometer is placed to measure these higher velocity areas of flow, making the published cfm figure even less representative of real life efficacy.

Computer fans use a static pressure rating in addition to cfm rating, and impeller blade design has a huge effect on this outcome. When attached to a computer heatsink a low cfm 120mm fan, like the Noctua [email protected] ~ 53cfm, but which has a high static pressure rating for its 1500 rpm, greatly outperforms fans with 70% higher CFM ratings and which also draw 2 and 3x the amperage, and create more noise while being less effective.

The 100 cfm duct booster fan, with its flat metal blades, relies solely on angle of attack of those blades to scavenge and push air. Such blades can be easily stalled when enough resistance is placed to the airflow, and even a smooth duct presents a surprising amount of restriction. These fans work best when the air they are moving already has some momentum from another fan.

The computer fans blades are foiled nicely and rely not only on the angle of attack but this airfoil to efficiently move the air.

The centrifugal fans like the Broan unit are basic and effective, but are wasteful of electricity. I have one similar looking design, and while I cannot easily measure airflow out of the 3 inch vent, I did measure amp draw, and at 77 watts, decided against employing it to scavenge air from my workshop ceiling. Seems this centrifugal design is much less affected by restriction, and is perhaps why your 50cfm broan fan is outperforming the 100cfm duct booster in yuour subjective impressions of efficacy.

The amount of restriction out your rafter is likely an area for improvement of efficacy.

As I want heat evacuation without relying on the power grid, and with everything locked up and me gone, and I have solar and some batteries already set up, I employed some 120 and 140mm 12v computer fans, and a cardboard divided housing which forces their flow out a rafter at roof apex.

The 120mm fan is rated at 74cfm and 0.24 amps and does actually draw that much. Some computer fan ratings are the start up surge, like the 140mm fan next to it, which claims 7 amps, but I've only measured just over 5.5 on the start up surge. I have put this 140mm fan on its own switch, and control the speed/ voltage via a modified voltage bucker. Flat out at 12.8v input, this 140mm fan draws about 3.25 amps and turns 4k+ rpm and is very loud. If placed face down on a flat surface will levitate about 1/4 inch over it. Its 7 large wide blades jut well forward and are a low angle of attack, for a very high static pressure rating, but considering the noise made and amp draw, it has a comparatively low cfm rating. I have another 140mm fan with more fan blades, shorter and higher angle of attack and a 2.3 amp rating, which in free air moves significantly more air at higher velocity, but it cannot levitate itself, the blades just stall.

I only turn on the 140mm fan at generally no more than 0.7 amps of draw via my voltage bucker, come afternoon, but the 120mm fan is fed battery voltage directly, 24/7, and when I open the workshop door late morning, it is still cooler inside than out, whereas before i added this 12v exhaust shroud the opposite was true.

The combination of radiant barrier and exhausting the ceiling can be taken to unneeded extremes, but its nice to not bake in one's own workshop on the hottest of days.

I want to remove the grid entirely from my workshop ventilation, but the 20 inch box fan with 20x20 suction from ceiling shroud is hard to beat in terms of effectively replacing interior air with outside air. Placing it on an inverter at high speed is ~430 watts though, and I only have a 100 watt solar panel feeding my 190Ah of Deka intimidator AGM.

In terms of efficiently exhausting air, for low wattage consumption/ noise, the computer fans are hard to beat, but 230mm seems to be their largest size, and those in this size range are just low rpm designs and many would be needed.

There are 115VAC computer fans, but much less options than their 12vDC counterparts. I think even if I did not have batteries to power my ventilation I would be using the 12v fans on a transformer/ switching power supply as the amount of design and thought that goes into the computer fans by companies like Noctua, Delta and others, makes fans like the inline duct booster fan into a joke of design.
 
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