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External peltier box

post #1 of 4
Thread Starter 
One problem with various forms of extreme cooling is condensation. Would it work to put the cooling & therefore the condensation in a different chamber than the PC?

I do not need a pretty machine or exposed innards & would definitely rather not have a bunch of flashing lights; I just want it to work well. Here's the design I am currently thinking of, which I'd probably build in a 19" rack since those are dirt cheap used & a good place for things like a UPS, router, ethernet hub, ....

Upper chamber has a pretty much conventional air-cooled PC in a desktop case, maybe with some big heat sinks glued on. The trick is that the ambient temperature around it is about 5 C, 41 F, because of cold air blown in from the lower chamber. There are one or more fans -- preferably one big 30 cm or 12" unit -- blowing right on the bottom of the case and an air outlet above the center of the top so airflow goes around the whole case. The chamber is well insulated for both sound & heat, probably with big slabs of styrofoam. I won't mind if it is somewhat ugly and it might not be with fabric covers or some such.

The lower chamber has sides about 30 by 50 cm, 12 by 19 inches and one is an insulated door; the floor is also insulated. The other three sides are sandwiches, two big aluminum heat sinks with peltier units between them. You want the whole thing to be capable of cooling whatever load the PC presents. I figure for my rig 900 watts total, 300 per side, should do it. All the condensation should happen in the lower chamber & it should be fairly easy to arrange drainage for that. The actual PC gets de-humidified cold air and it would be easy to add a dust filter so it gets clean air as well.

Except for being distinctly bulky and possibly rather ugly, this sounds awfully good to me. What do others think?
post #2 of 4
Air is an extremely poor heat conductor.
You're going to waste a lot of energy cooling the air down below the dew point (Google latent heat).
Just blowing the air over peltiers isn't going to dehumidify it enough.

Other that that it should work.with much more air flow and much larger heat transfer surfaces. You need to work out the math. Just saying X watt of heat and 2X(?) watts of cooling doesn't account for heat transfer inefficiencies.
Edited by billbartuska - 7/22/16 at 2:32pm
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post #3 of 4
Quote:
Originally Posted by Pashley View Post

One problem with various forms of extreme cooling is condensation. Would it work to put the cooling & therefore the condensation in a different chamber than the PC?

I do not need a pretty machine or exposed innards & would definitely rather not have a bunch of flashing lights; I just want it to work well. Here's the design I am currently thinking of, which I'd probably build in a 19" rack since those are dirt cheap used & a good place for things like a UPS, router, ethernet hub, ....

Upper chamber has a pretty much conventional air-cooled PC in a desktop case, maybe with some big heat sinks glued on. The trick is that the ambient temperature around it is about 5 C, 41 F, because of cold air blown in from the lower chamber. There are one or more fans -- preferably one big 30 cm or 12" unit -- blowing right on the bottom of the case and an air outlet above the center of the top so airflow goes around the whole case. The chamber is well insulated for both sound & heat, probably with big slabs of styrofoam. I won't mind if it is somewhat ugly and it might not be with fabric covers or some such.

The lower chamber has sides about 30 by 50 cm, 12 by 19 inches and one is an insulated door; the floor is also insulated. The other three sides are sandwiches, two big aluminum heat sinks with peltier units between them. You want the whole thing to be capable of cooling whatever load the PC presents. I figure for my rig 900 watts total, 300 per side, should do it. All the condensation should happen in the lower chamber & it should be fairly easy to arrange drainage for that. The actual PC gets de-humidified cold air and it would be easy to add a dust filter so it gets clean air as well.

Except for being distinctly bulky and possibly rather ugly, this sounds awfully good to me. What do others think?

what your looking for is a chill box.
http://www.overclock.net/t/1533164/the-24-7-sub-zero-liquid-chillbox-club
I am building one myself for my PC as I do not want condensation.
http://www.overclock.net/t/1584867/tec-chill-box-chamber-build-log
post #4 of 4
You will need very powerful peltiers, much more powerful than simply the heat load of the computer. You need to cool all the air moving through the case to 5°C and I assume you aren't going to have the flow rate tuned such that the air leaves the case near ambient temperature (that would defeat the purpose, you might as well just to water cool if you want to cool to ambient temperatures). This means you need to remove the extra heat from all the air moving through the case, not only the air that is actually heated by the computer. This could be a lot of air too, I am not sure how efficient the heat exchange would be in the top chamber but a single NH-D15 reports a max flow rate of 140,2 m³/h.

Using 25°C Air at 60% humidity going to 5°C Air at 100% humidity:

100% humidity at 25°C = 0.0203 kg/kg * 0.6 = 0.01218 kg/kg

56.17 kJ/kg = (1.006 kJ/kg°C) (25°C) + (0.01218 kg/kg) [(1.84 kJ/kg°C) (25°C) + (2501 kJ/kg)] | (25.15 + 0.56 + 30.46 = 56.17)

17.58 kJ/kg = (1.006 kJ/kg°C) (5°C) + (0.0050 kg/kg) [(1.84 kJ/kg°C) (5°C) + (2501 kJ/kg)] | (5.03 + 0.046 + 12.505)

56.17-17.58 = 38.59 kJ/kg

at 5°C 100% humidity ( x = 0.0050 kg/kg, ρda = 1.2690 kg/m³):
ρ = ρda (1 + x) / (1 + 1.609 x )
ρ = 1.2652 kg/m³

At 140.2 m³/h:
140.2 m³/h * 1.2652 kg/m³ * 38.59 kJ/kg * (1h / 3600s) = 1.901 kW

1901 Watts of cooling needed just to cool the max flow rate of air through a NH-D15 from 25°C (and 60% humidity) to 5°C. A lot of the energy required is due to condensing the water out of the air so at a higher humidity it would require more power to hit 5°C.

Maybe vent the cool dry air exiting the top of the case past the external heatsinks somehow? That way you reclaim some of the energy by improving the efficiency of the peltiers.

edit: I decided to add back 500W of heat to the 140.2m³/h 5°C air flow to represent the computer's heat and calculate what the exhaust air temperature would be.

17.58 kJ/kg + 10.15 kJ/kg = (1.006 kJ/kg°C) (X°C) + (0.0050 kg/kg) [(1.84 kJ/kg°C) (X°C) + (2501 kJ/kg)]
27.73 kJ/kg = 1.006X + 0.0092X + 12.505
X = 15.00°C exhaust temperature

Not very impressive really, the air is below ambient but the CPU temperature would not be <25°C; water cooling seems more effective. You need a lot more than 1901W of cooling for a good chill box.

edit2: I also decided to calculate the amount of water produced in the bottom chamber, 0.7956 L/h. Snorkle.gif
Edited by Asmodian - 7/22/16 at 4:08pm
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