Remote Living > Heating
A look at Peltier cooling
dnix71:
I wonder how NASA does it? The EV suits all have some kind of solid state temp control, but maybe they are smart about it, since in space if you face the sun your back is to deep space.
One side hot, one side cold. You could run a Peltier backwards like that make power.
Multiple modules isn't done commonly because cheap is king in this world.
http://www.mobilegas.co.uk/mobilecoolbox/proelectriccoolbox/tropicool.htm Here is a Peltier fridge with an "insulation bridge" to limit heat flow backwards in power off mode.
joestue:
what i'm saying is the amount of heat flowing backwards throught the junction depends on the temperature difference, the amount of heat flowing forwards depends on the current.
the two are independant. this is why at constant amperage the amount of heat flowing through the junction is linear. 0 at typically 60C temp difference, and x amount at 0C.
those small induciton motor driven compressors are exceedingly inefficient.
If you were to cut the top off, take the stator out and rewind it for three phase, hook it up to a small 3 phase motor driver (you could use those 24/48 volt airplane motor drivers, they aren't that expensive)
and drive it at say 600 rpm instead of 1700 or 3400 you'd use a lot less power.
DanG:
The best efficiency range from thermoelectric devices is 30 to 60%.
7 watts over 24 hours will chill 7 gallons of water 10°F.
It takes .018btu to cool one cuft of (dry) air 1°F, or takes 0.0002197 watt to cool 1 cuft of (dry) air 1°F.
In worst-case real-world small-scale food refrigeration, say tropical oceans keeping hull at 90°F, water temp at 86°F, phase-change cooling regularly achieves 180% input-output gains while thermoelectric at its theoretical very best stays at 30 to 60%.
Space suits are cooled by allowing liquid water to seep through a porous plate and sublimate from solid to gas phase directly into space.
Small DC powered freon compressors use an inverter module power adapter - most of them have an adjustment for RPM, some variable but most are a fixed value resistor that can be changed to control RPM.
zap:
--- Quote from: DanG on February 10, 2011, 07:01:50 AM ---
In worst-case real-world small-scale food refrigeration, say tropical oceans keeping hull at 90°F, water temp at 86°F, phase-change cooling regularly achieves 180% input-output gains
--- End quote ---
???
ghurd:
I am not an expert on Peltiers, except on how to cook one in world record time. :(
Am I following this correctly?
My take on it is 9W is better than 70W, and the things cost $4 each, and RE is expensive.
So $40 saves a lot of RE power.
I think the same way with LEDs. Run more at lower power and higher efficiency to achieve the same result with less power for just a bit more money up front.
G-
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