X-Message-Number: 2051 From: R. Ettinger Subject: Thermoelectric Cooling I have appended below Robert Ettinger's replies to the March 20 - 26 CryoNet messages concerning thermoelectric cooling. Kevin Q. Brown ----- March 30, 1993 From: Robert Ettinger To: Wowk & Correspondents Subject: Thermoelectric Cooling Brian Wowk has had some good ideas for using thermoelectric effects in regulation of a cold room, and then has proposed it for the actual cooling, and asked whether his cost projections are not too good to be true. I'm afraid they are. First, a minor quibble or two. Mr. Wowk uses "Peltier effect" for both the actual Peltier effect (using a potential difference to produce a temperature difference) and its inverse, the Seebeck effect (using a temperature difference to produce a voltage). If you want a generic term, you could say "Thomson effect," which includes the others. Also, he uses the term "efficiency" of a refrigerator when he means "coefficient of performance." The efficiency of any system is defined as the useful work output divided by the energy input, and can never be more than 100%, while the coefficient of performance of a refrigerator, the ratio of the heat extracted to the energy input, can be more than 100%. Now: Mr. Wowk uses a heat engine formula to show--correctly--that in the ideal case, operating between 143 K and 283 K, the coefficient of performance is greater than 1. He then guesses that, in an actual case, the coefficient might be only half of that, which would still be good. Unfortunately, that guess is almost certainly much too optimistic. I don't have hard numbers, but I'm almost certain of this on a common sense basis, as follows. First, Peltier kitchen refrigerators are not competitive, although they are said to be getting closer. Second, heat pumps for home heating are apparently sold almost exclusively in the warmer states where there isn't much heating load, and even there they are premium priced compared even to electric baseboard heating, which in turn is maybe three times as expensive (ongoing) as fuel heating. I think this indirect evidence is nearly conclusive--that we would have to pay a high premium price for thermoelectric cooling. Eventually--as I pointed out in The Prospect of Immortality and at various times since--we may be willing to pay a premium price to get both energy (thermopiles) and refrigeration (Peltier cooling) without moving parts or purchased supplies, a high capital cost but virtually no maintenance or ongoing cost, giving us cherished reliability and independence. That time is getting closer, but I don't think it is here yet. We probably still need better transistor junctions and maybe better superconductors (since Joule heating is one of the major problems in Peltier cooling). I wish I had something more positive to say about this, but this aspect of Mr. Wowk's cold room probably won't be realized for a while. ----- Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2051