Re: [PSUBS-MAILIST] fridge vs. Ice CALCULATIONS - psub air conditioner

[Alex <spm2@nomad.ignorelist.com>]

Maybe you could get one of those 12v mini fridges and put the condenser (the
hot side coils) either outside the psub somehow or have some kind of heat
exchanger to the outside water. Then you just have to put your food, beer and
ice inside it and then when you want to cool off inside the psub you can just
leave the door open.

If you get a fridge that takes 15 amps that'll be 180 Watt
s, so you could expect it to put out maybe 600 Watts of cold air. A 5,000
BTU windor air conditioner unit used to cool a room in a house down takes 500
Watts and puts out 1464 Watts of cooling capacity.

Ice requires 220,000J / kg to melt it, and 4220J to raise 1kg by one degree K
after it melts. So it takes about 42200J to raise it up to 10 deg C. In total
your 1kg of water will put out about 262,000 Joules. A Joule is 1 Watt*second so
262,000 / 3600 = 72 Watts for an hour.

30 liters (kg) of ice will give you about 7,860,000J or 545 Watts of cooling for
4 hours. A 30 kg lead acid battery will put out 125 Watts for 4 hours at 50%
DOD, which is probably about 400 Watts of cooling, but you still the space that
the mini fridge takes up. The ice takes up about a 32cm square area, and you
have to haul in a new ice every 4 hours or so. I would go with the fridge. With
the fridge when you're not in the psub you can close the door and not use as
much power, and keep your food cool too. When the door is open you can put your
food in the little freezer compartment to keep it cool.

Alex



On 09-Aug-2010 ShellyDalg@aol.com wrote:
>  
> In a message dated 8/8/2010 9:04:26 P.M. Eastern Daylight Time,  
> spm2@nomad.ignorelist.com writes:
> 
> Is the  object of the psub air conditioner to lower the temperature to 
> below  the
> outside water temperature?
> 
> Alex
> 
> 
> 
> Hi Alex. I believe David's goal with this device is to provide a little  
> cooler air when a psub is on or near the surface. A psub submerged should
> cool 
>  down quickly but also heats up quickly when on the surface in an area like 
>  Florida.
>  It's been mid to high 90's here lately. The water temp is hovering  around 
> 84 degrees as measured at the beach but I'm pretty sure it drops rapidly  
> as the depth is increased.
> Now if we can figure out how to drop the humidity level in the air. Any  
> device being designed must be simple to operate, cheap to build, and use as  
> little precious battery power as possible.
> Frank D.

-- 
Mailed with XFmail on 10-Aug-2010.
God saved Noah, but Noah had to build an ark!



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