So this "air conditioning" thing is looking like a hit. Us in the rich northern hemisphere dig it plenty, which means that our sweat-shopping brethren in the south will be even hungrier for in once they can scratch up the dough/labor reform.
And at the same time, this ozone-eating refrigerant business just sucks. They say they're phasing out freon, but I say bullshit. It will take an all-out block-by-block invasion of China (and/or Monsanto) to close the books on that business.
So. Ridiculous growth industry, approaching environmental disaster. Well then!
So you know how refrigerators work, but let me remind you anyway:
1: A compressor, uh, compresses gaseous refrigerant (like freon), thus heating it up.
2: The hot refrigerant is cooled in a "heat dumper" heat exchanger (that heat going outside onto hapless sidewalk pedestrians), cooling it down to room temperature or so. In most modern systems the refrigerant condenses into a liquid here, but a phase change isn't required.
3: The medium-temperature refrigerant is expanded, thus making it way cold. In conventional condensed-liquid systems, this simply happens in a pressure-blowing "expansion valve". In all-gas systems, the refrigerant is expanded in some sort of engine.
4: The cold gaseous refrigerant goes through a "heat sucker" exchanger that sucks in heat from the building's inside air.
Keep in mind that the "heat-dumper" heat exchangers is a gas-to-gas type, unlike the liquid-to-gas type exemplified by a car's radiator. This is why a replacement car AC heat-dumping exchanger (aka "condenser") is more expensive than a new radiator, even though it's much smaller. Manufacturing a heat exchanger with all that exterior AND interior exchange area that doesn't also leak is a very tricky=pricey undertaking.
I have it on good faith from both theory and the literature that smaller temperature differences ("delta-T's") between the four steps above make for a more efficient, but necessarily bulkier and more expensive system. A lower delta-T across the condenser means that more exchange area (= $) is needed to reject the same amount of waste heat, etc. This is why Carrier requested a more stringent USA standard for AC efficiency (more money for them), and is also why Dick Cheney and His Idiotic Majesty said no (more money for them).
An air-conditioning system that uses no refrigerant at all, but air itself. The key component is basically a car-style turbocharger that is driven by a high-speed direct-drive electric motor.
So, to transpose from the four steps above:
1: The compressor side of the turbo unit compresses some air, thus naturally also heating it up.
2: That compressed air passes through the same kind of "heat dumper" heat exchanger, cooling down a bit.
3: The compressed-but-cooled air then passes through the turbine side of the turbo unit, coming out at ambient pressure, but colder than it was going in.
4: Um, there is no fourth step. There is no "heat sucker" exchanger with which to transfer heat from the building's interior air to the "refrigerant" (air). The cold "refrigerant" goes right out into the room and that's it.
So. Since this is a low delta-T process (the compression ratio of a single-stage radial-flow turbocharger-style compressor is limited to 3 or 4), the overall efficiency is high.
What's better is that the step 4 heat exchanger isn't even there, thus reducing the cost and reducing that step's delta-T to zero zero zero.
The "heat-sucker" heat exchanger from step 2 IS there, alas, and it'll be a whopper, too, since the system delta-T is low. However, the good news is that it can leak, since leaking a little air out into the atmosphere is perfectly OK. The step 2 heat exchanger thus be correspondingly and significantly cheapened.
That electric-driven compressor/turbine unit will be tricky, of course. The main speed bump will be integrating the high-speed electric drive into turbocharger body, and the rotor into the turbine shaft. Super-high surface speeds preclude cheap iron-based magnetic materials as well. It's still doable however, and straightforward to those who really know that sort of thing.
(Look at the one-piece compressor/turbine/generator in the <http://www.capstoneturbine.com>Capstone microturbine</a> for an example of that kind of direct-drive integration between a turbine electric machine.)
And then there's the reliability issue, since the thing must run for months at a time. Help is on the way, however! Check out how Capstone's turbine uses an air bearing. No friction! What a score. That's great, because it means that the friction/reliability issue has already been handled by someone, so we know it's not impossble.
And that's what I got. 'Could be neat.
Request for Help:
Turbine noise is more unnerving than compressor noise, so this probably wouldn't fly in a window-mounted unit. Can active sound cancellation help?
How small can the compresser/turbine/motor unit be before the efficiency goes to hell?
Below a certain size, is a free piston type of compressor/engine a better idea?
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birth: 3:20pm January 30th 1975, Beloit Wisconsin, 7lb 4oz (3.29kg)
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