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Old 01-17-2009, 02:45 AM   #1 (permalink)
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Workable a/c alternative

I've got this massage device that I place on a lounge chair and plug in. I love it.

While in massage heaven and watching a doco on the tube about thermoelectric devices I had a thought. It was lonely so I place it here.

A cigarette lighter powered car seat liner that has thermoelectric cooling built in to cool your back and make person cooler overall.

The thing with this idea is efficiency. None of the coolness produced would be wasted into the atmosphere but rather work directly on the object required to be cooled.

Cool idea or no?

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Old 01-17-2009, 12:57 PM   #2 (permalink)
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Thermoelectric cooling is very inefficient. COP of 0.4 or so.Your Rankine cycle AC is very efficient. COP of 3.0 routinely.

I have batted around the idea of using an adsoption machine for car AC. It would run off the exhaust and/or jacket water heat. Adsorption is also very inefficient (COP of 0.8 vs COP of 3.0 for Rankine cooling) but it has the virtue of being able to work OK with a very low temp heat input. Solar adsorption machines work A-OK with only 200 degree input heat. My thermstat is 203 degrees and my EGT (post turbo is in the 300 degree range.

Problem is that it is worthless until the vehicle gets warmed up enough to put out the requisite temps. So you have to retain the Rankine cycle unit. Also we now need ANOTHER condenser and it needs to be four times the size of the Rankine cycle condenser.

Doable, but a engineering problem.
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Old 01-17-2009, 12:59 PM   #3 (permalink)
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A very cool idea!

I think Lincoln (luxury division of Ford Motor Co.) had some Peltier effect seats that both heated you and cooled you. Probably not at the same time.

If the covers of a car's seat and seat back were perforated, IMHO even a humble little fan (or fans) inside there would provide noticeable cooling, even without thermoelectric coolers.

My pet idea is a perforated steering wheel with little hand cooling fans inside. Maybe--- to avoid wiring complexity --- the fans could be removable and rechargeable, maybe shaped like a lipstick case.

BMW had a rechargeable little flaslhight with its recharging dock in the glovebox, 1985 325e.

OTOH the steering wheels of today's cars must be full of wires, so, a few more wires for the teensy-weensy sweaty palm blowers wouldn't be that much of a challenge to manufacture.

The US Army has some efficient cooling vests, either in the works or else already in use in "hot places".

I've heard that the Peltier effect coolong isn't that efficient, but if it is a "targeted, localized cooling effect" so to speak, yes, I would guess you'd save energy in comparison with the typical A/C set-up blowing cold air everywhere and dragging down your fuel efficiency in the bargain.

[edit: Big Dave, what if the thermo-electric isn't trying to cool the cabin but only oldpecan's butt?][has anyone compared the comfort/energy ratios of those two different cooling strategies?]

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Old 01-17-2009, 03:26 PM   #4 (permalink)
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Aww heck, I just noticed there are already some ideas out there for the a/c seat, re previous threads.

And i thought I was pretty clever...
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Old 01-17-2009, 03:46 PM   #5 (permalink)
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exhaust/cooling sys.

Quote:
Originally Posted by Big Dave View Post
Thermoelectric cooling is very inefficient. COP of 0.4 or so.Your Rankine cycle AC is very efficient. COP of 3.0 routinely.

I have batted around the idea of using an adsoption machine for car AC. It would run off the exhaust and/or jacket water heat. Adsorption is also very inefficient (COP of 0.8 vs COP of 3.0 for Rankine cooling) but it has the virtue of being able to work OK with a very low temp heat input. Solar adsorption machines work A-OK with only 200 degree input heat. My thermstat is 203 degrees and my EGT (post turbo is in the 300 degree range.

Problem is that it is worthless until the vehicle gets warmed up enough to put out the requisite temps. So you have to retain the Rankine cycle unit. Also we now need ANOTHER condenser and it needs to be four times the size of the Rankine cycle condenser.

Doable, but a engineering problem.
Big Dave,in Israel,solar ponds are used to gather and store heat,and heat-exchangers are submerged in the ponds,which contain a working fluid like 134-A which goes superheat,is expanded through a turbo-generator,pumped to a raised pressure to allow condensation back to a liquid at ambient temperature,then returned to repeat the cycle.They skip the lithium bromide absorption cycle with low efficiency,opting for the mechanical cycle.----------- For long I've believed that such a system could be boot-strapped onto vehicles to take advantage of waste heat.The system could also generate electric power,be completely hermetically sealed like any refrigeration unit.Do you see any potential for such a device?Obviously,for short commutes,it would be worthless,but for extended travel,the 66% waste heat of the I.C. engine would provide enormous energy input.And if the refrigeration cooled only the "occupants" and not the entire cabin,their would be "scaling" advantages as far as Btu requirements.
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Old 01-17-2009, 03:50 PM   #6 (permalink)
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Just read through some previous threads and this

Amazon.com: Wagan Universal-Fit Air Circulating Ventilated Seat Cushion: Automotive

was suggested. What about connecting the air intake to a small chiller box with a ice pack. With a properly insulated chiller box I imagine an ice pack could last a couple of hours... Its been hot here in NZ...

Seems easy, cheap and effective?
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Old 01-17-2009, 03:54 PM   #7 (permalink)
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Waste heat recycling, converting to 13.8v(turn off alternator) and a/c like coolness seems the best way to go.

Is this technology readily available to ecomodders at a suitable cost?
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Old 01-18-2009, 01:16 PM   #8 (permalink)
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Low delta-T Rankine cycle machinery is A-OK in stationary applications where huge collectors and heat rejecters are possible. That doesn't sound like something usable on a car, particularly a small car. At a low delta-T, these equipment gets very large (and heavy and expensive) for the amount of power (air conditioning) produced. Just that pesky Second Law ofThermodynamics in action.

What might work on a bigger vehicle, like my F-350, is to get the smallest 12volt RV frig you can find and use it as a water chiller to provide cool water for a driver cooling vest/chaps. Fighter planes, particularly ground attack planes use these to efficiently cool the pilots.
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Old 01-25-2009, 12:34 PM   #9 (permalink)
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here's a Renault concept car that minimzes accessory power consumption; it heats ONLY the STEERING WHEEL:

Renault looks to wee-hued windows to cut car power draw • Register Hardware

if your hands are warm, YOU'RE warm... ... ... ... ... ... right?
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Old 01-25-2009, 01:05 PM   #10 (permalink)
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Simplest, cheapest alternative A/C? A spray bottle of water. Works pretty good, especially in dry climates.

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