We have two containers for storing equipment at Scouts. We suffer from condensation in one of them and even when I finish insulating the ceiling I think it will be a problem.
I am thinking of an extractor fan to get the moist air out, but do I need to add heat, another vent or are there better solutions.
Cost and DIY ability are obvious limitations!
Thanks
Desiccant wheel dehumidifier with a permanent drain.
You get air circulation, a little heat and operation down to .
However, they will cost more to run that other solutions.
Where's the water coming from?
If the container is well sealed then I would use a dehumidifier, which would warm as well as dry the air, possibly with a humidistat. They are expensive to run 24/7 as they do take 100 or more watts.
If not well sealed then perhaps ensure the the container is off the ground and apply even more ventilation?
How insulated?
The steel (high emissivity) radiates heat to the sky (approximate black body) on clear nights and can get well below the air temperature. Permeable insulation is useless since the water vapour penetrates it, condenses on the steel and saturates the insulation. It needs a continuous vapour barrier or closed cell material. detailing the insulation on chilled water pipes is a similar problem, any gaps in the vapour barrier (outside the insulation) and you get condensation dripping out at random points.
I saw a BRE (or BSRIA?) digest years ago on steel roofs, it was a common problem. I don't recall the findings. I think you may need external insulation.
Either a dehumidifier or an extractor fan that comes on only when temp and RH are such that it will reduce water vapour load. Desiccant wheel type dh required, not compressor or peltier based.
NT
What is the difference between the one with a problem and the one without? Does one of them have a leak of rainwater into it?
Chances are that the cold steel is radiating from the roof to the clear sky and then acting as a magnet for damp air and forming dew. Your best best is to paint the roof and sides with aluminium paint to minimise radiation losses and insulate the inside as best you can. This should also prevent excessive heating internally in the sunshine.
Vents at the top to let warm air out might help too provided that they are weather proof.
Solar powered fan or simply passive solar warm air rises and roof vents of some sort would be my suggestion. You only want to exchange air with the outside of the container when there is warm dry air available.
The guy with the big industrial steel garage door condensation problems has the same issues as you will have.
Good point.
Maybe one has a hole, vent, unsealed door, etc., that allows air in from outside but not rain. As water vapour condenses inside, the water vapour in the outside will migrate in to the container since it then has a lower vapour pressure.
Even a "new" standard shipping container will not be air tight.
Jim K
Agreed, but one may actually be leaking rainwater into its internal space if there is one good one and one bad one. A wooden shed is much better behaved in this respect since wood doesn't supercool at night.
er well, I was responding to the flawed theory of one having a "hole,vent, unsealed door" through which damp air **but not rain** enters etc..
...my point being *both* containers will have air leaks (even new ones are not air tight)
Indeed.
Jim K
Are they different materials? Steel, aluminium and GRP are all used for cladding containers.
Colin Bignell
Not completely air tight, but some will be more airtight than others. Water vapour will migrate in through any openings. The question was, what is the difference between the two.
More openings = more condensation.
They can be sufficiently airtight to asphyxiate stowaways or float for several weeks, though not at the same time.
In article , Onetap writes
Sorry - one of them has our tents and cooking gear in it - which is why we are more concerned - the other has less perishable items. Both suffer the same. Partly it is everytime we open it we tend to take moisture in with us.
floating for several weeks is a function of their contents being lighter than water, not that they are airtight- (as anyone with any experience of them would know...)
Jim K
Remove the illegal immigrants?
outside but not rain. As water vapour condenses inside, the water vapour i n the outside will migrate in to the container since it then has a lower va pour pressure.
After checking for leaks, question what is in them, how often they are open ed and for how long compared to one another and is one set on a slight slop e?
How much would it cost to spray-foam the walls and ceiling of the damp one? Once coated you could improve it with something cheaper; plasterboard or w hatever? You would need a vent in the roof though. Something fairly large, with a bo x above and maybe a small fan below. Put a dozen holes on a high rib and se al around them with silicone and put a box over that to keep rain out. A co mputer fan below and pray you haven't torn it.
It wouldn't have to be all that powerful, a large computer fan might do, as all the damp will be at the highest point inside initially. Meanwhile you should get some desiccant. It is cheap enough and easily recharged with the empty oven after Sunday's dinner.
That might even solve the problem if you never leave it too long.Four feet of troughing along the top of a side should do; swap the charge over at eve ry meeting, depending on the weather. See how you get on.
om outside but not rain. As water vapour condenses inside, the water vapour in the outside will migrate in to the container since it then has a lower vapour pressure.
ened and for how long compared to one another and is one set on a slight sl ope?
e? Once coated you could improve it with something cheaper; plasterboard or whatever?
box above and maybe a small fan below. Put a dozen holes on a high rib and seal around them with silicone and put a box over that to keep rain out. A computer fan below and pray you haven't torn it.
as all the damp will be at the highest point inside initially. Meanwhile yo u should get some desiccant. It is cheap enough and easily recharged with t he empty oven after Sunday's dinner.
t of troughing along the top of a side should do; swap the charge over at e very meeting, depending on the weather. See how you get on.
Yes, but I think you're going OTT.
It seems to be a (fairly well) sealed steel box, the relevant points being that;
1) the steel gets baking hot in sunlight (as does a parked car) evaporatin g any water; 2) the steel can cool below the air temperature on a clear night, and act s as a condenser plate and water drips where it's not wanted. 3) the water volume is small, and comes from the damp(ish) contents with some probably infiltrating from the external air.Sealing, intercepting & removing the water (internal gutter &/or moisture trap dehumidifier) seems the best way to progress. Introducing ventilation introduces more air & moisture. A moisture trap will give an idea of the water volumes to be removed daily , even if it proves uneconomic in the long-term. A bulk supply of calcium chloride would probably make it economical.
The spray-on insulation is fine, but costly (for scouts) & is marketed at those who use containers as offices or homes & so have a constant ingress of moisture and have the most problems with damp. The sealed box probably doesn't need this.
Thank you for your advice so far. Having had a good look it was obvious that there was more water/vapour inside that outside since wet mud gets walked in, the tents are often slightly damp, etc, and then the door gets sealed.
The addition of a cheap extractor fan (on time switch) and a few holes at the opposite end has already reduced the amount of condensation on the roof dramatically.
I am going to monitor the situation for the next week or so but we also want to put a small amount of heat in there to reduce the risk of damp in the canvas, etc.
Thanks for the advice and will keep you posted.
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