Re: [PSUBS-MAILIST] Condensation in a psub

[Jon Wallace <jonw@psubs.org>]

Paul,

Just looking at the unit specs and your estimate of 1.7oz/hour of human 
water vapor output, it appears this unit would not be able to handle the 
water vapor added by respiration, and have no effect on the overall 
cabin humidity.  I used http://www.bom.gov.au/lam/humiditycalc.shtml as 
a reference and had to calculate back and forth between metric, but this 
is what I came up with.

1) 86F = 30C = .95oz water per cubic meter @ 80% relative humidity
2) 3 feet x 7 feet = 50 cubic feet = 15.24 cubic meters = area of 
typical small sub (did not include area of tank heads)
3) 15.24 x .95 = 12.8 oz of water in cabin @ 30C / 80%RH ( 86F / 80%RH )
4) 20.5oz/day = .85oz/hr = efficiency of dehumidifier unit
5) 1.7oz/hr = human respiration

The unit could only be expected to slow the rate of water vapor being 
added to the cabin by respiration, and even then only by about 50%.  In 
a starting environment of 86F/80%RH it wouldn't even be worth turning 
the unit on.  However, at 60F and 40%RH it would likely help delay the 
effects of condensation.  How useful the device is compared to other 
alternatives we've discussed is unknown since I haven't seen any data 
that describes the efficiency of other methods (desiccant for example).  
I'm not sure that anything other than a cabin flush is going to help a 
cabin that starts out at 86F / 80%RH.

Jon



Paul Lassen wrote:
> I was just wondering about this problem of condensation myself after noticing a picture on Emile's KSS / Garabaldi wreck photo album of the camera man wiping the inside of the main viewport with a towel to (presumably) get rid of the condensation. I've done some poking around and found that a good figure for calculating water output of the occupants is about 50 ml / hr per person, higher if the occupants are "stressed". That's about 1.7 US fluid ounces / hr. per person for our non-metric friends. I also found a solid-state dehumidifier product that might be suitable to modify and perhaps put in line with a CO2 scrubber. It draws 72 watts and can run on 12 volt power. It will pull out 20 oz. of water a day from air that is 86º F and 80% RH. I don't have any idea how that translates to performance in the temperatures and RH conditions common in a Psub. Does anyone out there know how to calculate that? The product is the EDV 2200 which can be seen at 
>
> http://www.eva-dry.com/images/products_2200.jpg
>
> The MSRP is $119.95 US but it seems to retail on other sites for around $70.00.
>
> I suppose that a canister of silica gel in line with the scrubber is probably better from a power consumption point of view.
>
>   





************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 53
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************