Re: High tech gadget?

[Bill Wichers <billw at waveform_net>]

As someone that has played with these (not for aquariums, but the same
technology), there are a few things I thought I should mention.
 
>not require plumbing (other than drilling the holes for the bulkhead 
>fittings), and they are relatively energy efficient compared to a 
>compressor.  Goeman did state that the IceProbe would cool a 
>"fully-insulated" 10 gallon tank 20 degrees F below ambient, so the actual 
>performance of the unit can be tweaked some.

They are not as efficient as you might think. The device doing the work in
these solid state chillers is called a "peltier junction", which is an
array of PN junctions (a little like half a transistor) that allow an
electrical current to transport heat in a direction depending on the
polarity of the electrical supply. I'm not sure about the actual physics
beyond that, but that is the basic idea. There is better info at
http://www.electracool.com/moduleworking.htm

What you need to know is that peltier junctions generate a *LOT* of heat
themselves in the process of moving heat. The units are only 50% efficient,
so if you are pulling 100 watts out of your tank, you are also generating
100 watts of heat in the module so you have 200 watts to get rid of. Some
of that heat will also "leak" back to the cold side of the peltier element,
so there will be added inefficiencies there. All that heat then must be
dissipated in a very small area RIGHT NEXT TO the COLD SIDE. You can't have
a large seperation between the hot and cold areas like you can with a
freon-based chiller.

Freon-type chillers will be a better (and certainly more economical) way to
achieve a large cooling capacity. I don't think you'd be able to get enough
peltier-based chillers in your tank to match the cooling capacity of a
small freon chiller. The peltier units are excellent for portable
applications like transporting sensitive fish in a bucket though,
especially considering that most can run on the 13-14 volts DC in your car.

     -Bill

*****************************
Waveform Technology
UNIX Systems Administrator