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RE: [hreg] Solar Air Conditioners

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  • Robert Johnston
    Thanks, Mike. Regarding your responses to the numbered points: 2. Good point. I hear so much more about PV, though (I think it is more
    Message 1 of 28 , Sep 9, 2001
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      Thanks, Mike.

      Regarding your responses to the numbered points:

      2. Good point. I hear so much more about PV, though (I think it is more
      "clean"/"elegant"/"sexy" than thermal technologies), that I wonder if the
      thermal arena doesn't still have some significant untapped potential. In
      particular, with new materials invented constantly, I should think this
      could continue to be developed.

      3. If you get a chance, I'd be curious to know the curve. Actually, I
      should look it up in my CRC Handbook. I wouldn't be surprised if it is
      in there.

      4. Sometime I'll have to root around and see what has been done here since
      the last I read about it. I think there is some potential here. What I
      is that it could be readily supplemented by gas or wood burning, so one
      still get by even off-grid on overcast/rainy days.

      5. It is a good INSULATOR? Really! I would have thought it to be a
      I thought those moon rocks were high in iron and other metals. Is planetary
      soil a lot different than moonrocks? I assume we're talking about Mars.
      Of course, upon reflection, I suppose that for a material to be a good
      radiator on a planet you're really talking about black body radiation rather
      than conduction of heat to the atmosphere. That's different than on earth.
      Is the atmospheric pressure on Mars lower than on earth?

      6. The one I know of was a consortium that included a pretty major
      in rubber elasticity theory at the Univ. of Cincinnati, Prof. James Mark.
      wouldn't of course use rubber banks as in the bands you buy at the office
      supply store. More likely you'd use just a handful of very large bands.
      key is to minimize hysteretic losses, so perfect endlinked networks are
      which is why J. Mark was involved, since he is an expert on endlinked


      -----Original Message-----
      From: Mike Ewert [mailto:mike.ewert@...]
      Sent: Saturday, September 08, 2001 3:20 PM
      To: hreg@yahoogroups.com
      Subject: RE: [hreg] Solar Air Conditioners

      Robert, I hope I can answer all your questions. They are good ones. You're
      an inventor at heart, aren't you?

      2. The conclusion I drew is that, although PV efficiency is low,
      refrigeration cycle efficiency is low for the thermal cycles, so the net
      "solar coefficient of performance" is similar for the 2 types of systems.
      Given that vapor compression and absorption heat pumps and solar thermal
      collectors are all more mature than PV, I expect the most progress in PV
      vapor compression refrigeration systems in the next 10 years.

      I have not followed up on Bergquam.

      3. Vacuum pumps take quite a bit of power. I suspect that is why they have
      only been used for cryogenic insulation systems. I have a reference for
      pressure vs. thermal resistance but I'll have to look for it at work.

      4. Cost, I guess. I think there is hope.

      5. Planetary soil (regolith) is a very good insulator. I suppose some day
      we may make things out of it, but I'm not sure if it will ever make good

      6. Yes, we have had some "rubber band" cooling system proposals. I don't
      think we have funded any. It just didn't seem practical how many bands you
      would have to have to provide significant cooling.

      -----Original Message-----
      From: Robert Johnston [mailto:rjohnsto@...]
      Sent: Wednesday, September 05, 2001 10:16 PM
      To: hreg@yahoogroups.com
      Subject: RE: [hreg] Solar Air Conditioners

      It took me awhile to find time to read the paper; thanks for sharing it!
      Here are a few comments/questions...

      1. (Comment--anyone else reading this paper in MS Word should note that in
      p. 2 there is a formatting glitch [at least in my installation of Word 2000]
      that makes the text jump from near the top of the first column to the top of
      the 2nd column, and then continue on the 1st column after a paragraph. If
      you have trouble making sense of that section, maybe this document did the
      same thing on your system as it did on mine).

      2. Mike, given the low efficiencies and high costs of PV, it seems
      inefficient and costly to do the schemes that use PV to drive vapor
      compression heat pumps. Yet that is what you spent much of the paper
      describing. I assume this is because that is what NASA sees as most suited
      to space (especially where cost doesn't matter). But for terrestrial
      applications, doesn't your review suggest that solar thermal heat engines
      would be the better way to go? If so, why not more work in that area (or
      did you just not choose to focus on it in your review)? (You did mention an
      interesting study in Sacramento, CA (Bergquam, et al, 1997)--any updates on
      the second phase of that study using evacuated tube solar collectors)?
      Seems to me that with metallized plastics, one could readily make a low cost
      trough concentrator. Not true?

      3. We've discussed this briefly in the past (I lost all my email due to
      computer glitch, so forgive me if I repeat earlier questions), but after
      your lab tour a couple years ago, I was wondering what the barriers to
      efficient vacuum insulation were, and you mentioned they were hard to
      fabricate. I've been wondering, what if you had a dynamic system? E.g.,
      what if your house insulation were cheaper vacuum panels that may have
      pinhole leaks but which are actively pumped by a vacuum pump to maintain
      insulation? The vacuum could be removed if it were desirable for heat
      transfer purposes to remove the insulation (e.g., maybe at night you'd
      remove it in the spring and fall to allow cooling of the home interior, or
      maybe on sunny mild winter days you'd remove it to allow heat into the
      house). Then it could be reapplied if needed for insulation again.
      Probably crazy idea, but what do you think? I suspect your answer will be
      that to effectively insulate, you have to get a SUPER vacuum so it isn't
      practical to do this, e.g., would require a two stage vaccuum pump and long
      pumping times, but thought I'd ask. Do you happen to have a good reference
      for vacuum pressure vs. insulation ability (R value or something)? What is
      the vacuum pressure in your test refrigerator vacuum panels in the lab?

      4. Why haven't solar regenerated dessicant systems found more use? Why
      couldn't you combine that kind of trying with some of the techniques like
      cool water tubes (see separate discussion with Kim, LaVerne Williams) to
      have dry cool air/thermal mass?

      5. I was curious about this conclusion: "Engineering trade-off studies
      have shown that with current technology, vapor compression heat pumps have a
      distinct mass advantage over thermally driven heat pumps for human
      spacecraft and planetary base cooling (Ewert, 1993) (Swanson, 1993). The
      thermal heat pumps have lower coefficients of performance and thus need to
      reject a large amount of relatively low temperature waste heat. In space
      there is no atmospheric heat sink and heat rejection must be via thermal
      radiation. This means larger, heavier radiators for the thermal control
      system, leading to higher launch-to-orbit costs." While true in space, is
      it true for planetary base cooling? Why couldn't you use the planetary soil
      to build radiators? For example, what if you pulverized it to a powder,
      mixed it with a binder, and molded it? A relatively small mass of binder
      would enable large mass of radiator. Or, maybe just use the planet surface
      as a heat sink (perhaps after shielding it with aluminized film), with fluid
      circulating in pipes buried beneath the surface. Just wondering; seemed
      like the planet itself was an untapped resource...

      6. Elastomers/rubber undergo heating/cooling during stretching/retraction.
      I've seen proposals (I think even funded by NBS) to use elastomers as
      refrigerants in heat pumps, replacing the gas with an elastomer undergoing
      cyclic mechanical deformation. Right now I can't see how that would
      necessarily help you in solar, but just curious if you'd run across it in
      your reading.

      Thanks for your comments,

      Robert Johnston

      -----Original Message-----
      From: Mike Ewert [mailto:mike.ewert@...]
      Sent: Tuesday, September 04, 2001 8:32 AM
      To: hreg@yahoogroups.com
      Subject: RE: [hreg] Solar Air Conditioners

      Here is a review paper I did a while back on solar AC and heat pumps.

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