That's a 25 degree (F) [13 C] differential. Remember, heat pumps "move" the heat from one area to another. In essence, a heat pump would be trying to "heat all outdoors" - or the entire lake, as the case may be.
One calorie per gram (of water) per degree - it is going to take a lot of calories out of your boat to raise the temp of the lake from
48C to 49C. That is what you have to work with.
snipped-for-privacy@hamster.jcbsbsdomain.local:
The figures I think are wrong are Karl's 9 btu to melt a lb. of ice. The numbers I learned in high school were 144 btu's per lb of ice.
Karl is no dummy. But he must be thinking of something else.
Dan
" snipped-for-privacy@krl.org" fired this volley in news:c5ef16f3- snipped-for-privacy@i2g2000yqm.googlegroups.com:
And you're right.
The "ton" is confusing, too. Most people think the 12K BTU is the amount of energy necessary to melt a ton of ice -- not so, it's the amount of energy PER HOUR to melt one ton in 24 hours.
So the total energy required would be 288,000 BTU, and of course, one two-thousanth of that would be 144 BTU.
LLoyd
FWIW... that last can put the boat cooling project in perspective.
Let's say the cabin was small enough to cool with a 5000BTU AC.
That's 5/12 of a ton, so it would take 5/12 ton of water ice to provide the same cooling capacity (ignoring the other thing about extra calories derived from raising the temperature of the water)
Airgas corp. says dry ice has three times the cooling capacity per pound as does water ice.
So now we only require 5/36 ton of dry ice to cool that cabin for 24 hours.
So that's what... about 278 pounds!
LLoyd
Or put up a picture of Al Gore and get some darts . . .
How about powering your existing AC unit from a portable gasoline or diesel fueled welder/generator? I've seen many of these with 12 volt battery charging outputs. Art
[ ... ]
On a boat? Likely so, most of the time.
Enjoy, DoN.
-- Most powerful is he who has himself in his own power. -- Seneca
Here is what I got this morning from Geof.
You only get 241 BTUs/Lb of dry ice.
5000 BTU/241 = 20.7 LBs of dry ice/hr or about 500 lbs/day. Cost/lb > $1, so at minimum you're spending $500/day My 16000 BTU AC can't keep up with 100 degree temps. A 5K unit certainly can't.
That's an important point, of course.
MY boat is 26 feet long, 10 feet beam, and displaces about 6000 pounds. Call is 500 cubic feet of interior volume.
That much water would be way over weight - a large water bed could weight 2500 to 3000 pounds!
Not to mention what could happen when tacking!
Ok, it was a hair-brained idea.
But an interesting discussion.
Ah yes, :) the global-warming types would have a fit - and I'd have to wear a heavy coat (at least!).
Pete, start a rain dance.
Do you know why a rain dance always works? It's because you don't stop dancing until it rains!
The thought has wandered through my head a few times.
120 vac units are cheap, and other than disposing of the hot air, easy to use.And 12 volts to charge batteries would be a God send after a couple of days.
I think someone is missing the boat by not offering just such a thing for sailboat use. Probably the liability factor?
Here's a few of them.
But if you had something more like a couple of hot water bottles with tubes connected to them so a 12 volt bilge pump could change the water a couple of times an hour................or maybe something like an air mattress half filled with water.
Dan
Dan
The build-it-yourself approach has a lot of merit, except for...
The two big gotchas for me are:
1) physical size of the system, where could it be mounted?2) it MUST be OUTSIDE the boat. (There is no place inside this boat that it would be safe to have gasoline vapors).
Somewhere along that link I saw an old 500 watt Honda gen set. THAT would be perfect. Small, Light, and enough power to handle our needs. Alas, they are not made anymore...
While dry ice is really cold, I don't think it has a huge amount of heat capacity. So, you might do a lot better with blocks of water ice, which might be cheaper too!
Most heat transfer fluids will turn to slush or worse when exposed to dry ice temperatures, so you may have real problems keeping the fluid flowing. Probably 200 gallons of Fluorinert would break your budget.
And, of course, the dry ice will generate HUGE amounts of CO2, great to keep fires from starting on the boat, but otherwise kind of a problem. What you may not understand is that you are going to need TONS of dry ice to keep it cool for 4 days straight in a warm climate. Huge amounts of insulation may help, most boats have none at all.
Jon
Are you talking about air conditioning while at a mooring or under way?
In the tropics everyone has a canopy they put up when moored. Usually full length but at least covering the "living" part of the boat which drops the deck temperature quite a bit. Another scheme is a canopy and big fans, regular 14" or larger floor fans with the pedestal taken off and hung in the boat.
A heat pump sucking up seawater and pumping it through a radiator with a fan blowing air through it might also help.Use a submersible bilge pump and a small car radiator or car heater radiator to test the idea.
Worth fooling around with... I'll dig around and see what I have to mess with. If this is a workable solution at all, we could just tie into one of the existing thru-hull valves and pick up water there.
Mostly it's at the mooring. Under weigh the wind helps keep us cool, and you are busy. But at anchor, and especially at night while trying to sleep, temperature becomes a big factor.
"J. Clarke" on Sat, 10 Sep 2011 15:17:33 -0400 typed in rec.crafts.metalworking the following:
You can do that anyway. I'm not "environmentally sensitive" - I'm cheap! CO2 doesn't grow on trees you know, and it ain't free!
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