Condensation on Sun Tunnel

I posted this on another thread about condensation on windows. It would be cheap enough to try. Maybe even the rain x for windshields. Never heard back from the other guy. Running fans to circulate air might help also.

If air is real damp, maybe a dehumidifier.

http://www.rainx.com/Products/Windshield_Treatment/Anti-Fog.aspx

two good ideas, rain-x and small solar powered fan just beneat the dome.Especially good since I am off the grid, Thankx,Redbaron

Maybe small low rpm solar powered fans up near the globe for some air circulation near the top?

Suggest double glazing to reduce thermal gradient and dehumidifier if RH goes above ~60%.

IMHO indoor RH of 40-60% is quite comfortable. When I moved into my current house, I had condensation problems begin at 65% RH on pipes and windows in my basement. RH would occasionally rise to 90%+ (yikes!) and my shop tools started to develop a rusty patina. I quickly purchased a dehumidifier to limit RH to 60% during those warm/wet months. It has been running well for over 7 years and only adds about $2-$3 to my monthly electric bill (Apr-Sept). Forced air heating plus cold weather (Oct-Mar) automatically limits my basement RH to comfortable levels. My problem solved. Good luck on yours.

From a physics viewpoint, you are getting condensation because the surface temperature of your light tube is below the dew point of the nearby air. You have two options. increase the temperature of the light tube or lower the dew point of the air. If your earth sheltered home is new construction, you can expect elevated dew point until the concrete cures. This could take many months. A dehumidifier would be a good first start.

If both ends are covered, I'd try to seal them as best as possible. Try blowing dry air perhaps from a hair drier then closing them. You might also try a bag of silica gel desiccant in the tube someplace relatively unnoticed. The bag might not have to stay permanently if the tubes seal well.

This may seem counter intuitive at first....

Install a small ceramic bearing computer fan - about 80mm, at the top of the tube, to drive air into the tube and the slowly force ventilate the building.

That, a 5W solar panel and a small battery....

Ceradyna makes brilliant fans that have a mean time till bearing failure of about 300,000 hours.

What you have is a distillation apparatus, with you being the steam source and the cool outside as your condensation point.

The best way to stop this is to make the light conduit fully sealed and moisture free. A few people have suggested this. Being plastic, it should be easy to seal the bottom with glass or acrylic, as well as the top. Getting it dry by adsorption or filling with dry air will work. But it must be sealed.

Clear plastic film allows too much moisture to penetrate, unless you use thick crystal clear acrylic. A silicon bead will seal the bottom. The top of the light tube should already be waterproof, but should also be sealed against gas penetration.

They do this with thermopane windows, 2 pieces of glass with dry argon/air between them.

The only other way is to seal it on the inside and vent the upper part to the outside. Make sure you have a fine screen in the vent, or you may have an ideal wasp home

GA. I am not sure if a double bubble (2 layers of plastic or glass like thermal pane) is available or would even work in this sun tunnel. I like the idea of sealing the bottom of the tube and sealing a dry area inside the tunnel. Interesting house (or bomb shelter) and I have seen one built on an island nearby Wolfe Island. Not sure what this house has for humidity issues. It did have a quarter moon glassed in entrance area and is on grid. No AC and very little heating required.

close the tubes on both sides with glass and fill them with Nitrogen. That would prevent condensation!

Take a soap bar and make a cross. This was method used during WWI on glasses of gas mask to prevent fogging and it had worked perfect.