Using crawl space circulated air to cool an adjacent shop??


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Old 06-18-14, 06:44 PM
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Question Using crawl space circulated air to cool an adjacent shop??

I have a new home in Virginia. The crawl space has a plastic liner. I can nearly stand up in the crawl on the back side of the house. It was nearly 100 degrees today but the crawl space was in the 60s.

The crawl space abuts the garage and a workshop through a cinder block wall. The workshop is essentially a one-car garage with a door to outside and door to the functional garage. There is no HVAC in the shop.

The crawl space is adjacent to the shop, through a cinder block wall. Has anyone used a fan to force some cool air into a garage or workshop from the crawl space? Any reason why this would not work?

Of note, the workshop is not connected to the main living space of the home.
 
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Old 06-18-14, 08:22 PM
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No, but I've thought about using the cooler crawlspace air to circulate in our house. So your post interests me. Seems to me that if you draw the air from the crawlspace through a large air filter, like the ones used for AC returns, the air should be clean enough. But, you will also need a vent to allow air from the garage to be drawn back into the crawlspace to compensate for what you are pulling into the garage.
 
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Old 06-18-14, 10:33 PM
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As far as using that air to help cool the garage I don't see an issue except that there is only a limited amount of cooling BTU's you can extract from the crawl space.

In my opinion... I don't think you'd want to use the air from a crawl space inside a house.
 
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Old 06-19-14, 06:33 AM
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PJ is correct that the cooling capabilities of a crawlspace will probably not handle the heat load from your workshop. In addition, the replacement air (hot and humid) will carry a lot of moisture into that cool crawl and may lead to rot and mold issues. In addition, in case more reasons are needed, the air quality in a cool 95% sealed crawlspace is not a source you would want to bring into your home or work shop. Yes, a crawlspace can be sealed and conditioned to function just like living space, but simply covering the floor with a plastic lined isn't sufficient. In most cases it involves rigid insulation on the walls as well and that defeats extracting any "cool" from that space.

Bud
 
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Old 06-19-14, 07:13 AM
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Good point Bud9051 about the hot, humid air going back into the crawlspace. I am sealing the vents in my crawlspace (in South Carolina) to stop this very thing. But I don't understand why rigid insulation defeats extracting the cool from the crawlspace. I would think just the opposite, i.e., the insulation would enhance the coolness by reducing the heat exchange through the foundation perimeter. Incidentally, I have a remote thermometer and humidity sensor in my crawlspace and the temperature has not exceeded 72 so far this summer.
 
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Old 06-19-14, 07:27 AM
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We are hijacking diyar's thread but it is related, but here are two links that may help.

The first will show a fully conditioned crawlspace (photo #5) and the second is a humidity calculator to convert outside 90 air at 80% RH to 72 and see what happens to the RH.

BSI-009: New Light In Crawlspaces — Building Science Information

Temperature, Dewpoint, and Relative Humidity Calculator

Bud
 
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Old 06-19-14, 08:37 AM
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Thanks. I plan to read your references later this evening.
 
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Old 06-19-14, 07:33 PM
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Well, I found the first article interesting, though complicated. I came away with the impression that the best solution to prevent joists from rotting and floors from mold damage is to apply foil backed foam insulation to the bottom edge of the floor joists. But, since he didn't say anything about closing the crawlspace vents, I'm not convince that his solution is necessary. In my case I had noticed water dripping from the floor insulation and joist bottoms last summer. But, so far this summer, after closing off most of the vents, I haven't seen this. Still, the humidity in the crawlspace is staying 90% or higher. I'm planning on sealing the seams on the ground cover plastic, running it up the walls about 1 1/2', and sealing the remaining vents when time permits. Once I get the ground sealed and vents sealed, I expect the humidity will gradually go down.

Getting back to diyar's interest in using some of the crawlspace cool air to cool the garage, I would probably try that myself if it wasn't a big hassle to create the passage between the crawlspace and garage. But, I would monitor the humidity in the crawlspace to make sure moisture didn't build up and create dampness on the joists. I would just use a small box fan, like you can get for about $20 at Wal Mart, and run it on low, at least at first, then go from there.
 
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Old 06-19-14, 07:58 PM
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Once you seal the vents and seal the floor covering the walls will still be providing some moisture. The photo #5 I mentioned resolves this by covering the walls with a low permeable rigid foam. They don't want a plastic barrier as moisture will just build up behind the plastic and find a way through. Evaporating it slowly to the inside keeps it under control. But then you have to decide how to manage the humidity. If you air condition the house you can share some of that dry air with the crawl. Or you can run a dehumidifier. Either way, you need to get the RH down below 50% to prevent strange things from growing.

The dripping you mentioned is a very advanced indication of a real problem. But 90% humidity still needs some help.

Bud
 
 

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