maybe relative in a way? last year I'd connected a 12v 1 GPM 0.32A pump through a 6x9" automotive heater core, with two 3.5" 12v 0.25A 45 CFM computer case fans pulling air through the heater core. on a 100 degree day, 85 degrees of lake cooled air is noticeably nicer, at about 0.8A. 80-90 CFM of air can change-cool a 5x6x6 (180 cu ft) cabin about once every 2 minutes, in my slow little electric runabout toy, sitting in near chest deep cooler air helps lots. (the bow and bench seat area might be 35-40 cu ft total with the fans straight at ya) the 1 GPM pump, probably changes out that heater core 10x a minute or more, and if the lake temp is 70-75 F, air out being about 10 degrees more, still nicer than 100+. it'd probably cool even moreso if there were 2 cores stacked for 4" thick off the same pump, but that'd also be a little extra with its plumbing (not anything difficult). in freshwater, a through hull water cooled heatsink might do good things with peltier? passive solid, or pumped water (at cost to batteries of course), its pretty easy for me to visualize making the cooler latch in to make the physical contact required. dont they lower temp internal to what they see as temp external? (I'm sure no expert!) if they drop temp about 40F, then starting at 70-75F would be nearer frozen than it seeing 90F. not that it matters to me that only goes out half a day or so, where a gallon jug or a couple 2 liter bottles frozen solid in a typical ice chest lasts plenty long enough.
--- On Wed, 10/24/12, John Francis <surv69@gmail.com> wrote:
From: John Francis <surv69@gmail.com>
Subject: Re: [Electric Boats] Re: 12V Accessories (Refrigeration)
To: electricboats@yahoogroups.com
Date: Wednesday, October 24, 2012, 9:21 AM
As to the cooling effect of water on a heat sink . . .
Since you're in water anyway(esp if you're in fresh water), why not make a reservoir(container) of water that "drips" water over the hot side of the peltier heat sink. Sure . . . you'd have to refill the reservoir every once in a while, but hey . . . the water's all around you anyway and best of all . . . it's real simple . . . I like simple and cheap and will compromise being able to freeze things for being able to keep things cool.
John Francis Newport 28 On Wed, Oct 24, 2012 at 7:13 AM, John Green <v_2jgree@operamail.com> wrote: Hi, Kirk, thanks for the response......sorry but I don't understand the reference to 'tons'. I realise that an auto compressor creates cold quickly, and that I don't need that, but surely the HP required at, say, one 20th or one 50th of the RPM is less than at the speed the compressor is driven by a car engine? I suppose a better question I should have asked is "Can automotive AC systems work at lower RPM, and if so, what are the RPM limits if any?" Maybe I ought to just try turning a car compressor with a ratchet wrench, but they tend to have little room around them. I know that at idle, they produce frost on exposed pipes. And I know that they are power hogs at the design speeds driven on a vehicle. What I don't know is if the losses at lower outputs exceed the production rates at those same outputs, assuming reasonable heat insulation. The solar panels I have will have no spare capacity most of the time, but if the HP requirement is low enough, the cooler/fridge application might lend itself also to pedal power - any electricity savings obviously represent increased range and/or lower battery discharge levels for propulsion. It might be possible, too, to combine a compressor system with a Peltier system, that could be used when moored etc. and when there are watts to spare, but I am currently not sure if various charging types, (ie solar and wind and backup ICE) can be combined for simultaneous use to keep the batteries 'up'. John Re: 12V Accessories (Refrigeration) Sat Oct 20, 2012 1:50 pm (PDT) . Posted by: "Kirk McLoren" kirkmcloren you lost it with small. An automobile compressor is sized, depending on application, at 1 to 2 tons. Lots of glass in a car and metal conducts well also. Rapid draw down is important. A sealed compressor with 1/8 that capacity will keep your cream cool. Assuming 50% efficiency mechanical work to electricity and then electricity to mechanical work you are at 1/4 horse versus 1 or 2. Besides in most warm places there is reliable sun. photovoltaics to battery to dedicated inverter is smaller and more reliable. My 2 cents. Will Rogers quote: "Stupidity got us into this â€" why can't it get us out?" -- http://www.fastmail.fm - mmm... Fastmail...
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