Re: [PSUBS-MAILIST] Humidity control

["Sean T. Stevenson" <cast55@telus.net>]

I would think that, with the possible exception of very short dives, in a 
small space (PSub size) the moisture present in the surface air that gets 
enclosed in the vessel is less significant than the moisture introduced by the 
occupants breath over the course of a dive?

-Sean


On Tuesday 15 March 2011 23:00:13 you wrote:
> We should probably write a white paper on this sometime since it seems
> to come up once or twice every year.  I always find condensation easier
> to understand in terms of dew point.  Simply put, and in all cases, if
> the temperature falls at or below the dew point, you're going to have
> condensation.  You can also get a sense of the relative humidity by
> comparing the current temperature against the dew point.  If the air
> temp is 80F and the dew point is 70F then you've got high humidity and a
> sticky humid day on your hands.  If the air temp is 80F and the dew
> point is 45F then you have low humidity and a nice dry day on your hands.
> 
> The problem starts at the surface when the air in your submarine is
> filled with the atmospheric conditions of whatever the current day is
> like.  Now consider that when a sub is in water the cabin air is
> eventually going to reach equilibrium with the water temperature.  If
> the water temperature is at or below the dew point of the atmospheric
> air, you can expect to have condensation issues as the air temperature
> in the sub begins to drop due to water conducting heat from the cabin
> through the hull.
> 
> In a high humidity situation (warm humid day, cool water temps), I think
> there's a simple and cheap solution that might go a long way to
> controlling condensation during the dive.  By emptying the air from an
> 80 cubic foot scuba tank into the submarine cabin just prior to closing
> the hatch, the dry air from the tank should displace enough of the humid
> air in the cabin to considerably lower the dew point inside the cabin
> and reduce the chance of condensation.  This should be easy enough to
> test without the sub even in the water by simply waiting for a humid day
> and monitoring the relative humidity in the sub before and after the air
> from the scuba tank fills the submarine.
> 
> For warm climates such as Florida, if you have room for the small
> "cooler" air conditioner that David Bartsch was working on last year, I
> think that could be an ideal solution for not only controlling heat in
> the cabin but also the humidity.
> 
> Calcium Chloride is cheap and easily available, and is suppose to act as
> a desiccant although I've never tried it.  The southern boys out there
> probably don't know about this stuff, but us northern boys usually have
> plenty of it on hand for melting snow and ice in the winter.
> 
> Jon



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