Cabinet Condensation

Wow, to pool water on a 12.5 square foot floor is a lot of water, too much for even the best desiccant to manage. You've applied a gasket to the cabinet door, do you need that? Air flow will help, a vent on top and an inlet on the bottom, both screened to keep insects and rodents out. Or possibly a fan in the vent on the roof, with an inlet in the bottom...

... and a drain for the (nearly) inevitable condensate.

Are the compressed gas cylinders just stored or is there gas cycled in (warm) and out (cold) of them?

Are you building ice on the tank wall in the evening when it is cold, then the ice melts during the day and runs to the floor? I have seen this happen on tanks of liquid CO2 and nitrogen which were used for modified atmosphere packaging in the food industry.

Doesn't have to be ice, just condensation from the atmosphere is the probable cause.

The surface of the tanks gets below the dew point at night and condenses on the tank surface, dripping to the floor.

Just put an insulating blanket on the tanks.

The surface of the metal tanks gets cooler than the ambient air causing condensation in the cabinet.

You have two choices:

1) Raise the internal temperature of the cabinet with an incandescent lightbulb or...

2) Wrap the tanks with a foam insulation blanket.

Where I live the conditions are similar to yours; 90 F in the daytime and mid 60s at night. It's also very humid where I live. I've seen condensation on the outside of cabinets that are outside at night; I've never seen condensation on the inside of them. So I'm wondering if the condensation builds up at night on the outside of the cabinet and seeps in somehow during the night and early morning; perhaps in spite of your gasket.

I'd check to see if there some other way that it can get in. I'd also think about covering the slab with 1/2" thick foam insulation board, around the base of the cabinet. The slab may be contributing to the condensation.

You are right. Of course it seeps in. Air at 90°F will expand. Air dropping to 60°F contracts, creating relative negative pressure.

Here is another vote for the idea that is the tanks getting cold as their contents are withdrawn. If insulating blankets are impractical, you could put a drip tray under the tanks, with a drain to the cabinet's exterior. If the ambient goes below freezing, use heat tracing on the drain. [?? Not sure that's the exact problem.]

Aerate the box, without air circulation you will never stop condensation.

Bazzer.

If the compressed gas is flammable I would hope that the cabinet is ventilated as per code.

Any time that you draw off from a liquid that changes to a gas you have a change in state. This will cause the remaining liquid to chill down. Condensation is inevitable.

Do not insulate your tanks, as this may affect the ability of the liquid to turn to vapour or it may trap moisture that will promote rust of the tank.

There is no gas escaping from the cylinders. These cylinders contain fire suppressant and will only discharge in the event of a fire. The discharge pipes exit the cabinet en route to the protected equipment. The annular space around these pipes is not sealed. My thinking is that moist air might be entering the cabinet here and condensing.

Now that I know this, then you are probably correct about moisture migration. Warm moist air will always go to a cooler area. The best example of this is in a walk in cooler or freezer when the vapour proof light fixtures start to fill up with water. It is a result of the electrical conduits to the lights not being sealed on the warm side of the box.

Just insulate the tanks and it will be fine.

Adding ventilation to the cabinet is also warranted, if it doesn't already have it, or it will deteriorate just like an unventilated roof.

I would also get the tanks off of the concrete or wood floor if possible just to avoid rusting and possible rupture of the tank.

"Do not insulate your tanks, as this may affect the ability of the liquid to turn to vapour..."

So, that's why the foam keeps falling off the Shuttle's main tank? ;-)

Probably a good point. Without knowing exact conditions and materials being used, unintended consequences may develop.

Correct GURU. The liquid must absorb heat to completely discharge. I cannot ventilate the cabinets as low temperatures during the winter will not allow all liquid to boil either. I have twin 5000 btu heaters installed for this purpose which will turn on at 40 deg F. The tanks are not rusting yet but obviously will soon. I have calculated seismic and wind loads on the system and cannot provide any wood supports. I believe the moist air entry is the culprit; some of you seem to agree.

If you can't set the tanks up on blocking or maybe treated wood furring strips, maybe you could paint the bottom 2" of the tanks with a urethane paint. Strip to bare metal then prime and paint. An epoxy primer makes a great undercoat for urethane finish. Only down side is that changing out bottles means either scratching the coating or losing the tank all together. An alternative I've seen are plastic or resin tank bottoms. I don't know where the guy found them but I thought they looked handy for stabilizing the tanks.

Even resting the tanks on a sheet of plexiglass would be better than concrete or wood.

Looks like you need to bump up the lower level for the heaters. Ideally, it would be good to use a microcontroller to sample temperature and humidity to determine the lower threshold due to the dew point. However, you just need to find a lower threshold the works for all conditions.

Have you tried talking to the manufactures of the tanks? They have to be dealing with this every day.

This is an unusual application for these tanks. Normally they would reside inside the hazard area they protect. In my case they are protecting a hazard area that has a 130 deg. ambient, at the upper limit of the tank functional range. My problem is not keeping the tanks from rusting but getting rid of the condensation altogether. That is an owner mandate.

I'd still contact the manufacture or the installer and at least see what they have to say.

You can accept or reject their opinion as you see fit.

After buttoning up the shed has not given you the results, than I suggest a dehumidifier in the shed, with the condensate piped outside. I would put a trap in the drain line to prevent moisture migration.

If you can not resolve the source of the moisture, you will a least be able to control it.

Be careful on the trap, make sure the vertical distance from the dehumidifier's drain to the flow line of the drain line is greater than than the flow line of the drain line to the bottom of the trap. Otherwise the head pressure in the trap will exceed the pressure to drain and it will back up. Another way to go is (an I can't remember if there's a drain in this storage unit but if there is...) run the drain line from the dehumidifier to the floor drain and leave an air-gap between the top water line of the drain hub and the bottom of the drain line. This will prevent back flow.

A condensate pump would also work.

It falls off, as they have not got their act together for the last twenty years. If they had actually listened the the boots on the ground and those engineers who had who actually understood the problems and resultant consequence's, and had the cajoles to speak up we might of not seen the "O" ring failure on the booster rockets or the damage done to a wing on lift off due to piece of foam insulation falling off the LH2/LOX tank.

We are not dealing with cryogenic fluids in this case. If we were he would be talking about ice build up.

Just like going outside in the morning before the sun warms things up, you'll see condensation on anything metal that is allowed to assume it's natural temperature at any given cool morning. Condensation is a function of water vapor (humidity) and temperature. Raising temperature or reducing humidity will alter the amount of condensation. As one respondent noted, even though the door is gasket-ed, humidity will pass to the inside. In fact it will probably be higher to to the temperature fluctuations he noted and the lack of conditioning or dehumidification. Raising the nighttime temperature above the dew point will work. Covering the metal surfaces with an insulated blanket will help. Ventilation to reduce humidity build up will help. BTW there are several good dew point calculators on the Web that you can use to anticipate what the condensation conditions will be.

I would agree that allowing air to flow through the cabinet would help.

I'm wondering why this matters. Are the tanks rusting? If so, it's probably at the base. Set the tanks on pallets or wood strips to prevent rust and allow air flow. Drill some holes in the bottom of the cabinet to allow airflow and as weep holes for condensate and forget about it.

Maybe the best suggestion. Ventilate and let it go. Unless you're storing liquid nitrogen or similar material that creates an exceptionally high temperature differential, I think most guys that store gas bottles do so in expanded metal cages. If L-N2 is being stored expect condensation even with the slightest RH.

Reading through this thread reminds me of schooling years ago. It would take me longer than most to explain what little I recall of this.

Suffice to say as others have that it's got to do with the change of temperature from the outside to the inside