Sweating metal building. Exhaust fan???

[Chris2]

So my last wooden pole barn (30x30x10) didn't sweat at all, doors faced north and south. My new all metal building (40x50x16) with two doors facing west and one facing east sweats like crazy. Not really sweating but condensation, all over everything this time of year. Ill literally have beaded up water all over anything metal.
So my question is do you guys think a 1700 CFM exhaust fan would help? Should i mount it up high near the roof, midway up the wall?
Close behind the East wall with one door there is a creek bottom and a pond. From the West wall with two doors the elevation is all up hill. Should I mount the fan blowing out of the East wall so as to not pull in the damp air from the creek bottom?
Thanks for the help.
Louisiana weather!

 

[RNeumann]

If this is an uninsulated and unconditioned space then it needs to be vented. The condensation is caused by temperature differences between inside and outside.

I don't think you need to install a fan at this point.

Start with something easy like a 12x24" vent down low in one corner and another high in the opposite corner. Put one on the side with the predominant wind and the other opposite that.

If you are able to balance the temps with just vents you won't need the fan. If the barn has windows leave a few open and see how that does.

 

[RNeumann]

Btw the issue has more to do with roof aspect and color instead of which direction the doors face. The roof is getting sun and warming the structure creating the temperature difference and condensation is the result- assuming you are not heating the barn.

 

[Texasmark]

Anytime a surface is below the ambient temperature dew point it will sweat if the relative humidity is adequate to support it....iced tea glass, loaded tractor tires, tractors, sheet metal buildings. To sweat you need moisture in the air aka relative humidity up. If you had a roof vent at the peak, natural convection would vent the air out of your shop. This helps to reduce the condition and is a recommendation. I had bubble roll insulation applied to my new barn prior to steel sheating to prevent this problem which it has. The ridge cap also has 10' vents every 20'. Floor is concrete with a vapor barrier between the concrete and cushion sand. Seldom do I have sweating of anything in the shop and when I do it's on a real damp day and you can see the water accumulate from the open door gradually moving across the shop wetting the floor and cooler objects.

The roof continues outside making a 15' overhang (uninsulated) for protected parking. Moisture runs down the sheating big time and when it gets to the wooden purlins, it accumulates and drops down on whatever is below.

I don't know if a blower (located high on the wall, would work or not but if a roof ridge vent works then why wouldn't a blower....same principle only forced vs natural convection. Only thing I think you would need to do would be to not turn it on with humid days, keeping your door closed as much as possible till the humidity dropped. Use it/them after the dew has burned off things or on non humid days. I usually keep my doors closed if not immediately in use on humid days and it really helps in keeping the floor and things inside dry.

On your location, yes you want to pull the drier air into the building so you want to pull from the hill side. 32000 cu ft at 1700 CFM = 18 minutes to replace contained air. I don't think I'd use up power and listen to it run all day. Turn in on half an hour before you close shop or better yet, turn it on around 2-3 pm when the air is dryest. On humid days leave it off....do more harm than good.

 

[chim]

Moving air doesn't always help and can hurt. The air being introduced into the building needs to be dryer than the air it's replacing.

Years ago I was on a new school project and the building's HVAC wasn't ready to operate. It was in the Spring and the humidity was high. The temperature of the steel structure in the building was lower than the dew point and there was some condensation on the columns. The superintendent for the GC brought in a few large fans to ventilate the building. The result was a much worse problem with condensation. Instead of the columns just sweating, there were little streams of water coming down from them. In areas where he had gotten the cart before the horse (ceiling tile ahead of the HVAC) the ceiling tile sagged down and was removed and taken to the dumpster.

 

[RNeumann]

BA-149: Field Testing Unvented Roofs with Asphalt Shingles in Cold and Hot-Humid Climates | Building Science Corporation

Condensation - Wikipedia

Dew point - Wikipedia

Solar gain - Wikipedia

Some interesting responses. Here are a few links to pertinent subjects. I'm thinking that understanding what is happening would be the place to start. Then we can move toward ways to prevent it.

 

[Chris2]

So a little more info. Yes the building is insulated (ceiling and walls) with double bubble. No ridge vent but the doors are 14'x14' roll-ups so with the doors closed the diameter is much smaller leaving a rather large gap between the door and the door frame acting as a vent. This gap is probably about 6" so that gives three 6"x14' openings at the top when the doors are closed.

 

[brown40]

I think if you have the eaves and ridge properly vented (theres formulas to determine how much surface area for your building to open up) you're in good shape for the moisture and heat to passively move out... the question is how much time you're swinging around the dew point and the metal provides the temperature differential to form droplets.
Even with open vents, ridge, eaves, and vapor barrier beneath the floor--I still see condensation on the floor and equipment in my building on humid days when conditions are wrong (3-6 days a year in temperate Maine). Unless you have a genuinely conditioned space you can't stop the differential--just try to manage it.
In your state with the extra sun and humidity, probably a power vent would help to move out the hot air once the sun goes down, They come with temperature and/or humidity activated controls.

 

[Texasmark]

So a little more info. Yes the building is insulated (ceiling and walls) with double bubble. No ridge vent

All the better. I'll iterate what I posted earler. I think it will work for you. Besides, it's the least involved solution and since you mentioned it, you are already considering the cost and installation. Sounds like a done deal.

 

[RNeumann]

The venting idea is sound but the reasoning, as stated, isn't. You are not trying to lower humidity with ventilation. You are trying to balance temperatures. If OP's tractor or metal object was outside I'm gathering he does not believe it would form condensation. The reason is because the temperature of the object is rising at or near the same speed as the air.....no condensation.
Move that object inside the barn and things are different. The solar gain on the structure heats the air inside the structure faster than the object (which receives no solar gain). When this occurs the object will form condensation from the temperature difference between the air and object.
The goal with moving air (mechanical or natural venting) is to mitigate the solar gain which will slow the warming process inside.
So, beyond the big ticket obvious exterior moisture issues like proper drainage around the structure, the goal is to slow temperature change. If the goal is to lower RH the OP needs to seal the structure and mechanically remove moisture.
Thoughts on a solution-
With an insulated structure this could go either way. Vent or not vent. It's time to experiment.

First air the place out to balance RH between inside and outside. Then leave 2 roll up doors on opposite sides up overnight and see if condensation forms. If not, continue to lower the doors daily until it does. This will give you an idea how much venting you will need. Assuming you don't have a good predominate wind from a different direction. The vent sizing can be slightly less if you are using the low and high venting suggested by a few folks as this creates some natural convection.

However, I'd also try this since it's insulated. Maybe the insulation can slow the temperature change enough that having the holes in the doors is the issue. In this scenario the goal would be to make the structure as air tight as possible. To do this the starting point is the same with airing the structure out to balance the RH. Then seal up the openings in the roll up doors and any other major sources of air infiltration. See what happens the next day. Maybe, just maybe, the insulation is slowing the temperature changes enough to prevent condensation.

Both of these experiments will cost little to nothing except some time. If objects outside aren't condensating but objects inside still are with doors fully open or everything sealed then it would be time to think about a fan on a switch that is reading temperature differences.