Man powered cooling and flying

The designs of cars, airplanes and houses are determined by cheap energy. When our own bodies supply the energy, the forms change. The bicycle,
canoe and man powered Gossamer Condor are interesting examples of design when energy is expensive.
Let us also build man powered air conditioners. It should be interesting, for Nature offers no examples; she only cools passively. Twenty-five years after the invention of the Condor, we have not graduated from cars and highways to commute silently like so many giant moths, but a man cooler might have great consequences.
Until recently man could not fly by his own power. He could fall, he could glide, he could rise on thermals, but until Paul McCready and the Gossamer Condor he could not fly, as birds do, by his own efforts. It wasn't for lack of trying. Old pictures show winged men leaping, racing and crashing, vainly trying to get airborne. A large prize for flying went unclaimed from 1959 until McCready's success in 1977.
We only cool ourselves passively. Passive cooling is giving heat to someplace cooler; by convection, if the air is cooler; by radiation, if cool is in sight; or, mysteriously and around corners, water will accept heat at temperatures far below that of the air if there is no traffic jam of humidity. Evaporation is why panting and sweating works so well to cool us animals. Water vapor finally condenses in a cold cloud or on the earth as dew.
The pilot sits on a bicycle seat pedaling a propeller to drive the 96' wing span, 70 lb. airplane. The cooler pedals a compressor on a similar seat in an insulated cabin that is covered inside and out with finned heat exchangers. Most air conditioners need 1 unit of work to pump out three units of heat. We wish the COP was 10 not 3. Then anyone would have a chance to pump out as much heat as he created on the treadmill, for most of us are at least 10% efficient.
Pedaling or cranking the compressor on an air conditioner lifts the heat to however high a temperature necessary to flow into surrounding air. This is real cooling, no relying on Nature's tricks. Sweating is no more real cooling than gliding is flying. Passive flying and cooling work only as long as one's weight or heat is headed for someplace lower.
The challenge to fly is different than to cool. Both depend on simple ratios - power-to-weight for flying and power-to-heat for cooling. While the athlete can affect his power-to-weight by trying hard, a burst of effort guarantees nothing for his power-to-heat ratio. More effort brings more heat, too. A flyer might fail on the cooler.
Washing out on the cooler is a familiar failure - like all those whose body does not obey the mind, the person who can't stop blushing, or who can't sleep, or worse, suffers an episode of embarrassing impotence. Imagine the desperate sinking pilot who discovers he becomes heavier by pumping harder.
The problem can be simply stated. To cool, the COP of the air conditioner multiplied by the efficiency of the man powering it must be greater than one.
The ASHRAE Handbook states people have efficiencies of 10% to 20%, and sales literature for air conditioners talk of COPs as high as 4.4. With a COP of 4.4 even a 20% efficient man could not crank or pump a standard air conditioner and cool. He does 10,000 ft. lbs. of work, adds 50,000 ft lbs. of heat, but pumps out only 44,000 ft. lbs. of heat. The temperature in the cubicle would rise higher and higher, yet the numbers are close enough to make one think with more investment in the air conditioner and training for the man things would work
Standard conditions should be air temperature above body temperature, 98 F.
The matching of man and machine will be interesting. The man can't get the job done by just being big and strong, or trying hard. He must be thermally potent, able to produce lots of power with little heat.
The machine is the passive partner and must be beautifully made with an efficient compressor and large heat exchangers. Like all joint efforts, there will be recriminations if things don't work.
Building a man powered man cooler is less dramatic, but finally more interesting than flying. Nature flies, but she leaves all her cooling to passive evaporation, conduction and radiation. Where she must have a high metabolism at high ambient temperatures, as with birds, she ups the body temperature and continues to cool passively. Doubtless, we will come to reflect on this if we build man coolers.
Perhaps the first man coolers will use elastic bands, liquid pistons or other Stirling engine components, not Freon refrigerants. They may be as different from conventional air conditioners as the Condor is from a jet airplane. After man coolers have been made to suit even the least efficient of us, someone will accidentally discover the real reward for our efforts. This invention made to cool man wants to run backwards, especially if its radiator is struck by sun. Although some would doubtless try to pass laws against it, God's thermodynamic laws would bless man coolers fed cheap, low temperature heat to power households.
The man cooler, dizzy, turning backwards, but forever obedient, could yield lots of work on a diet of 160 F heat discharged at 80 F.
No one could build these engines as engines; they will be too heavy, too large and too strange looking. Ridicule would defeat their designer. They can appear accidentally as I have explained.
Steve Baer September 2004
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ece.villanova.edu wrote some poetry: <snip>

All you need for this to be a world-beating idea is an insulated room, full of pedal-driven compressors, detatched from your main dwelling. Then, it's just a simple matter of herding your slaves in from the field to keep you cool. If you were really cashed up, say from your tobacco crop, you could even pay people to cool you down. Sounds like a winner to me.

What does this mean, please? I really want to know if you've found the secret to perpetual motion.
I'd like to see a human-cooled toilet cubicle, sort of the reverse of a tiny sauna. I'm sure an art gallery somewhere would buy it.
Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

could
crashing,
from
cool
at
humidity.
wing
in
exchangers.
the
body
the
harder.
one.
sales
of
lbs.
the
for
F.
the
thermally
efficient
yield
Interesting paper.
This research may never end in a functional cooler. But may bring unexpected discoveries and applications in very different areas. That's one of the most promising thing of energy downsizing.
Pardon my English and let me try to explain what I mean.
When the personal computer was invented in the 70's, it had so little power that IBM and big industries only laughed at it. But it brought new thinkings and led to new applications. The spreadsheet was invented by a student on a small computer. Never did the big computer folks could imagine it. They only used their computational power like brute force and not really tried to add more intelligence in the software.
With it's limited power, the personal computer had to innovate and invest in software. And it was not just a few dozens academic scientists in labs, but thousands of people everywhere with very different backgrounds. No surprise that the spreadsheet, word processor, games, graphics and so many different software applications popped up.
The same phenomena can be expected with downsizing energy generation. At present, utilities are just as the old IBM: they can only think big and therefore miss a whole field of research.
With decentralized power generation, millions of people will experiment different things. They will have to cope with the limitations and will have to invent the energy-software. And eventually new yet unknown applications. Some will try cooling, others will fly drones... no one knows yet what will come out but, if Earth is still a viable planet, we (or our children) will use these applications on a daily basis.
Who knows, some african or asian Einstein, now starving in a desert or a sweat shop may invent a personal energy-efficient plane that sells in billions...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ece.villanova.edu wrote in message

COP is not just limited by the design, but the operating temperatures. At PERFECT carnot efficiency:
COP=T(low)/(T(high)-T(low))
So if you wanted to keep a guy at, say, 80F (even with a PERFECT carnot engine), you'd have to be dumping into a 156F enviroment.

I'm not sure what your definition of cooling is, but anytime a given mass looses thermal energy, I define that as "real cooling".

That's probably a little underestimated. I've heard 30% in exersize physiology classes. 10% is probably stated to be conservative.

1. Human power is not cheaper than, say, gasoline power. Hire a guy at mimimum wage to power your A/C unit for one hour, then calculate how many gallons of gas you could have bought to power the A/C MANY times over (including operating costs of the engine) for the same amount.
2. Look at how much power is required to cool even a small house during summer conditions. Even with a VERY large efficiency, even 2 guys couldn't do it (ignoring their own body heat produced).
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Steve Baer wrote that...

Would you explain that in more detail?

I would too, according to physics. Steve makes a distinction between "passively losing heat to a lower-than-body temperature" (like gliding without thermals) and "active cooling to a higher-than-body temp."

This is a competitive R&D suggestion (like man-powered flight), vs a practical solution to the world's problems :-)
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com (David Harper) wrote in message

Nop COP equation is correct, but yor conclusion is wrong. COP is the ration of the amount of heat moved to the work required to do the moving, when moving it from the low temp to the high temp. If you are cooling a room at 80F and dumping to an outide radiator at 150F you need one amount of power, where as dumping to a radiator at 90F would require much less power.

Airconditioners could use a lot less power if they had much larger radiators. Of course large radiators cost a lot of $$$$ so as always it is a trade off between capital cost and operating cost. I built my own heat pump system for my house out of second hand stuff. Had radiators rated at 25 Kw condensing running at 2 Kw. My system used about 1/3 of the power of commercial unit.
With LARGE radiators cooling the room at 18C (64.4f) and outsife being 30C (86F) and a cycle at 50% of carnot cycle, assumption of 2 people being able to produce 500W combined, they could move 6 Kw of heat, while ( at 15 % eff fom them meaning that they radiate 3.3 Kw )a nett cooling of 2.7kw ( just a few rough figures ) :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@caverock.net.nz (Hamish) wrote in message

Right, my bad, however a COP of 10 would still be difficult under normal operating conditions even if your A/C could approach a perfect Carnot engine.

This statement isn't correct. You get to a point of limited returns. So long as the coolant is returning at about the same temperature as the thermal resevoir that you're dumping into, then you're ok. If it's still much hotter than the reservoir, THEN you need a bigger radiator.
For instance, if the coolant is returning at 100F, and the enviroment is 95F, then a bigger radiator wouldn't buy you much efficiency.
You can offset size requirement by just increasing the heat flux (as with a fan, like the one on most A/Cs, or with fins...or both).
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com (David Harper) wrote in message >

When I said
"Airconditioners could use a lot less power if they had much larger radiators"
It is correct, I just didn't add all the rest that you added. Yes going larger radiators is a game of diminshing returns.
Commercial units I have seen spit out hot air ( when heating the house ), with my home built unit the air fels cool, but it still gets the house warm fast, using much less power than an off the shelf unit because of the oversized radiators.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@caverock.net.nz (Hamish) wrote in message (David Harper) wrote in message >

Commercial A/C units have a large fan associated with the radiator so that they are keeping the coolant cool enough. This has the same effect as increasing the size of the radiator (adding a fan). A larger radiator on commercial A/C units won't buy you significantly more efficiency.

Warming your house? I thought we were talking about cooling.
Warming your house with large, internal radiators shouldn't buy you ANY more efficiency... it will just cool down your radiators and increase the surface area for a net gain of zero... since the end result is still your house's air.
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@caverock.net.nz (Hamish) wrote in message

Just because the radiators are rated to 25 Kw doesn't mean your system is removing 25 Kw of energy.
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@gmail.com (David Harper) wrote in message

Never said it was removing 25 kw, rated at 25 kw runnibg at 2kw
This means the condensing temp of the regeration gas is noticably lower than if it was running at he rated 25 Kw.
Any given radiator wil have an "overall heta transfer coeficient " essentialy in Kw per temp diff between the air and the condensing temp. To put twice as much heat through a given radiator roughly requires twice the temp diff
Hamish
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<sigh>
Another "cheap energy" pipedream, which, like all the others, works by complicating things sufficiently that we can't actually see what it's really all about.
Plants use sunlight, minerals, and water, to make stored chemical energy; and use some of it for themselves while they're at it. Animals eat plants to concentrate the chemical energy, and use most of it for themselves along the way. Humans eat plants and animals to concentrate the energy even further, and use little enough that there's some left over for pushing the pedals on a bicycle, a lightweight airplane, or whatever.
No matter how you slice it, though, this is just solar energy. And, with all the intermediaries between the sun and the end-user, it's an enormously inefficient form of solar energy. The only reason things like wood-burning stoves and other indirect solar processes work at all is that their total usage is tiny compared to the plant matter that's available for collecting sunlight, and compared to the time that collection requires. (Have you ever thought about how many YEARS of tree growth, and how many TONS of water and earth, are required to fuel just one evening's flames in a typical fireplace?)
If we increase the demand for plant-made energy even modestly, then the plant-stuff that converts the energy will need to increase too; but by a MUCH bigger factor.
When people talk about solar energy as a real alternative to fossil fuels, they often quote the (currently tiny) efficiency of available photo-voltaic devices (or photo-thermal ones, in the case of solar-furnace thingies); and calculate that it'd take zillions of acres of solar cells to produce any useful amount of energy. They're right, of course; but - without actually attempting calculations - I'm willing to bet that the acreage required to deliver solar energy through a biological food chain would be even larger.
The advantage (maybe) of using plants to collect energy instead of solar cells is that most of us like plants. They're pretty. They smell nice. And they do some other important stuff for our environment - like making oxygen. The bad news about plants is that they're sorta fussy about where we put them, and they just refuse to work without regular rations of water.
Human-made solar collectors (at the moment, anyway), are neither pretty, nor nice-smelling, nor helpful in the oxygen department. But they have one very important advantage: They don't need water. We could put them in places where neither plants nor animals are able (or willing) to live, and they'd make desert lands productive in ways that are currently impossible. Yes, It'll still take zillions of acres. But until we put solar collectors in space, the acreage is pretty much a given. If we can't find or make enough room for solar-cell farms, then we're surely not going to make enough room for plant-energy farms, either - or for all the zillions of critters we'd need to raise and eat in order to concentrate things enough so that we could pedal ourselves around.
Complicating the process, or making it less direct, might appeal to people who don't think real hard or real deep; but that doesn't mean that hopelessly inefficient schemes can be made workable just because we want them to be.
KG
snipped-for-privacy@ece.villanova.edu wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Kirk Gordon wrote:

Well, I'll agree that this whole human powered cooler thing is ridiculous but for other reasons. Mainly because people have already developed all the kinds of technology for cooling that he is ultimately aiming for past the "let's lower humanity to beasts of burden" stage.
...

Actually, solar thermal collectors (heating air or water) are much more efficient than photovoltaic and cheaper as well. It's just not as romantic to have a water heater and some air panels to take the chill off.
If you want to know how large something needs to be to do the job then you're gonna need numbers. PV panels are more efficient at converting sunlight into usable energy than plants by about one order of magnitude (10 times).

There are plants that grow in water, even salt water. Some of these can be very efficient at converting sunlight into hydrocarbons, almost as efficient at converting sunlight into useful energy as PV cells. Lucky for us, about 7/10th of our planet is covered in salt water. Besides, humans only use a small fraction of the total land area of the planet. No shortage of area or water.
I agree though, focus on the real goals instead of silly ideas like people powered ice machines.
Anthony
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Anthony Matonak wrote:

Yeah. I stayed away from ocean-based biology just to keep things short and simple. But no matter where it lives, a plant takes its sweet time collecting and storing energy. If, after only 100,000 years of (sorta) human existence, and only a handful of centuries of technological civilization, we're already overusing the biostuff (petroleum) that took millions of years (billions, maybe) to make and store, then what are the odds that ANY source, other than the sun itself, will satisfy us for very long. We could wreck the oceans (and the whole planet with them, maybe) by harvesting plant-energy there for a hundred years. Or maybe two or three hundred, for all I know. But then we'd be screwed again. And we could live on coal for a while, too, if we figure out how to burn it without choking ourselves to death. But when that's gone, we're right back where we started, only with more people, and more time gone by, and almost certainly with bigger than ever appetites for all the energy we can find.
EVERY plan that uses more than we get - in real time - from outside our world will eventually deplete the world and leave us broke. We have oil, right now, and coal, and oceans, and the beginnings of space-travel capability. We need to invest in the future, long term and for real, BEFORE our bank accounts run dry. Otherwise, when the day comes that we really CAN'T go pick some more free wattage off the energy tree, we won't have the resources, or the time, to do anything about it except lay down and die.
KG
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yeah, especially beets, figs, and sugar cane...
--
-john
wide-open at throttle dot info
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A great achievement, from a guy that I highly respect, but that technology has not come to much over the last quarter century.

Bad example: I am a certified flight instructor for sailplanes and I can tell you conclusively that flying gliders IS flying. In fact, it is a much greater challenge than normal (powered) flight. Your goal is to harness the energy of the sun to remain aloft.
Vaughn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.