Just a random thought about chillers

[BladeRunner]

Thanks for the timely explanation TerraMex was just about to disassemble my humidity sensor...... had lump hammer & chisel in my hands

Anyway I got a couple of MO's but don't remember them coming with temp sensors. Will try to work something in along those lines, I suppose the MO could be used to report humidity using a humidity sensor on one of the temp inputs (take some time to calibrate it fully though).

[Gooserider]

Bladerunner - I think you and TerraMex have the idea wrong, I suspect through a misunderstanding of exactly what your chart means.... I think that if you built the system the way you describe, it won't do very much, and might very well make your condensation problem WORSE!

Your chart describes the dew point, or what temperature condesation will occur at if the air is FULLY SATURATED with moisture. Or, in other words, given air at a particular temperature and relative humidity, how much it has to be chilled in order to have it reach full saturation and start condensing.

The term "Relative Humidity" describes the RATIO between the amount of water that a volume of air at the given temperature could theoretically hold, versus the amount that it is actually holding. (note that pressure also effects this, but not as much so, and can be ignored for our purposes) At least at the temperatures we are talking about (~10-60*C) cold air can hold less water vapour than hot air.

Thus if you take a given volume of air, and evaporate a specific amount of water into it, when you heat the air, it's relative humidty will DROP, and so will the dewpoint. If you cool the air, then it's relative humidity goes UP, along with it's dewpoint.

The most visible common example of this is a summertime thunderstorm - Air close to the ground is heated and becomes saturated with water, then rises as a 'thermal'. As it goes up, it cools, becomes super-saturated, and condenses, making a cloud. When the weight of the water in the cloud becomes more than the rising air can support, it falls as rain. The falling rain cools the thermal, shutting off it's flow, and the now unsupported water falls abruptly. (This is a gross over simplification of the process)

As another example, if you go into a dry heat type sauna (NOT a steam bath) with a cold can of Buttwiper (I wouldn't insult Guinness by cooling it that much!) you would not get much (if any) condensation on it, because the relative humidity is so low that the dewpoint is lower than the temperature of the beer can. (Once the experiment is completed you can cook some hot dogs with the lousy beer, and get a nice dark beer out of the properly non-functioning Lucas Electric beer cooler )

Now as it applies to your design proposal, what you seem to be trying to do as I understand it, is cool the air entering the case, without changing the amount of water vapour that it's carrying other than possibly having some condensation on the incoming air radiator (which really won't help much).

To pull some numbers off your chart, picking a fairly bad case scenario....

Assumptions - per your previous posts, and my guestimates....
1. Your rad is at 13*C and your blocks are at 12*C
2. Air going through the rad will be cooled 5*C from ambient.

Assume 30*C and 75% humidity (which the person from Southern Louisiana would consider wonderfully comfy...) The dewpoint is 25.1*C. Condensation would occur on your blocks at 12*C.

Run the air through the rad. it is now at 25*, and the dewpoint has now dropped to 20.3*, and condensation is still occurring on the blocks. Even with a really big drop to 20*, your dew point is at 15.4* and condensation is still happening.

But wait! you say, wouldn't there also be condensation on the rad? Yes, there would be, but the amount of water removed would only be enough to leave the air exiting the rad near saturation for the lower temperature. The dewpoint of air at 25*C and 95% humidity is 24.1*C, or ONE degree less than the result with no rad at all.... :shrug:

If I were trying to design something to deal with this, I would probably try to make a box with little or no airflow and try to dehumidify that air some how. Possibly you might also be able to do the same rad and chimney setup, only locating the CPU box ABOVE the chimney.

This way you make a sort of 'fanless dehumidifier' where the air would enter the rad, be cooled so as to get lots of condensation, and then reheated to ambient (or a bit higher) which effectively lowers it's relative humidity. If you can drop the humidity to 30% at 30*C by doing this, your dewpoint in the PC case becomes 10.5*C, and you'll have no condensation. (I would note though, that those numbers would leave less margin than I would feel really comfortable with...)

[TerraMex]

No , i think you're wrong on several issues.
But i (and Blade does too) do appreciate the input. Let the hostility begin .

Your chart describes the dew point, or what temperature condesation will occur at if the air is FULLY SATURATED with moisture.

If it's fully saturated then it has a relative humidity of 100%. That's the definition of fully saturated.
That's not what the chart means. It means that at a given relative percentagem of humidity, to diferent temperatures, when the condensation will occur. It doesnt have to be fully saturated.
I can have very low relative humidity and at low temperatures it will create condensation. More on that later.

At least at the temperatures we are talking about (~10-60*C) cold air can hold less water vapour than hot air.

That's one of the main points. But it's harder for a cold air to release the one it has, if it's a low value of relative humidity, to another cold point (relative cold). The delta T needs a minimum value.

Thus if you take a given volume of air, and evaporate a specific amount of water into it, when you heat the air, it's relative humidty will DROP, and so will the dewpoint. If you cool the air, then it's relative humidity goes UP, along with it's dewpoint.

If you have a given volume of air, with a given percentage of water vapor, if you evaporate an extra quantity of water vapor, then, for the same temperature, it will have a higher dew point. See the chart.

When you increase the temperature , for the same humidity level the dew point will increase. This goes against what we want.
We want to remove some humidity and maintain a cool temperature. If a good deal will precipitate on the rad, then , the air (still relatively cool) that goes through the case will have less humidity and lower dew point. See the chart. And that's what we want.

But I'm assuming the rad is very efficient on doing that.

The most visible common example of this is a summertime thunderstorm - Air close to the ground is heated and becomes saturated with water, then rises as a 'thermal'. As it goes up, it cools, becomes super-saturated, and condenses, making a cloud. When the weight of the water in the cloud becomes more than the rising air can support, it falls as rain. The falling rain cools the thermal, shutting off it's flow, and the now unsupported water falls abruptly. (This is a gross over simplification of the process)

Gross, but i get the point.

But this is better :

When moist air cools, a cloud can form. This much is true.
Sure, a cloud may form as the temperature drops, but not because some mystical holding capacity of the air has decreased.

The air (mainly nitrogen and oxygen) no more has a holding capacity for water vapor, than, say, water vapor has for nitrogen. The atmosphere is a mixture of gases. While saturation (which involves bonds between different molecules) is a real phenomenon in liquids it does not describe the interaction of atmospheric constituents.

Water molecules are constantly coursing back and forth between phases (another word for the three states: vapor, liquid, and solid). If more molecules are leaving a liquid surface than arriving, there is a net evaporation; if more arrive than leave, a net condensation. It is these relative flows of molecules which determine whether a cloud forms or evaporates, not some imaginary holding capacity that nitrogen or oxygen have for water vapor.

The rate at which vapor molecules arrive at a surface of liquid (cloud drop) or solid (ice crystal) depends upon the vapor pressure.

The rate at which vapor molecules leave the surface depends upon the characteristics of the surface. The number escaping varies with:

the phases involved --- molecules can escape from liquid more readily than from the solid (ice);
the shape of the boundary --- molecules escape more readily from highly curved (small) drops or ice crystals (convex);
the purity of the boundary --- foreign substances dissolved in the liquid or ice diminish the number of water molecules which can escape;
the temperature of the boundary --- at higher temperatures the molecules have more energy and can more readily escape.

The temperature of a cloud droplet or ice crystal will be (nearly) the same as that of the air, so people imagine that somehow the air was to blame. But, if the (other gases of the) air were removed, leaving everything else the same, condensation and evaporation would proceed as before (the air was irrelevant to the behavior).

What appears to be cloud-free air (virtually) always contains sub microscopic drops, but as evaporation exceeds condensation, the drops do not survive long after an initial chance clumping of molecules. As air is cooled, the evaporation rate decreases more rapidly than does the condensation rate with the result that there comes a temperature (the dew point temperature) where the evaporation is less than the condensation and a droplet can grow into a cloud drop.

Evaporation increases with temperature, not because the holding capacity of the air changes, but because the more energetic molecules can evaporate more readily (with, of course, the caveat that evaporation is also influenced by things other than temperature, as described above).

And when the temperature drops below the dew-point temperature, there is a net condensation and a cloud forms. This can even happen at ground level, fog, as an example.

Now as it applies to your design proposal, what you seem to be trying to do as I understand it, is cool the air entering the case, without changing the amount of water vapour that it's carrying other than possibly having some condensation on the incoming air radiator (which really won't help much).

Cool it and create condensation. Not one or two. Both. Both will change the dew point considerably (Bladerunner hopes). Assuming it can change by a large percentage, both the relative humidity and the temperature. But it's a big IF.

Assumptions - per your previous posts, and my guestimates...

Wrong assumptions, assume BladeRunners numbers.
Assume a 20º C ambient , average.
8ºC or less at radiator (or even average 10ºC). No forced air.
The issue is how much the temperature drops as it passes the rad.
And how much a drop of relative humidity.

But wait! you say, wouldn't there also be condensation on the rad?

On the contrary, for me anyway, as stated. You misread. I stated condensation will occur, probably. Again, depends on the rad.

But honestly, if the rad reduced enough the temperature of the rising air, it will be suficient to avoid any type of condensation without tampering with the relative humidity. Given the chart that is.

And you forget that Bladerunner stated that the cooling loop will be cooling pelts, so the water wont be that cold, and the interior wont need very low temps.

[TerraMex]

Damn, i gotta stop making big posts.
Forgot to make a comment.

---
Dehumidifiers solve the high relative humidity (RH) problem by simply pulling the moisture out of the air.

A small fan pulls the rooms humid air into the dehumidifier and the air is passed through a cooling coil and is chilled to its dew point on a cold surface where condensation occurs, similar to a refrigerator. The condensation then is then released into a bucket or is released through a hose. The moisture reduced air is then heated back to room temperature and blown out into the room.
----

But. Because of the non fan setup pictured by BladeRunner, the air current formed (theory) wont maintain a very low temperature after passing through the radiator. In fact it will be cooler than ambient, but the cooling system is already cooler than ambient as it is , in particulary the blocks and tubes (due to the nature of BR setup). So no harm done there , assuming not that large detal T. It will (theory) have less RH , which is the whole point. Cooler than ambient, less RH , very low risk of condensation . In theory of course.

It's all very nice in theory but only by testing it (IMO) can be see what are the real flaws. Alot of tweaking can be done , shape , size, temperature of the chimney, etc etc etc.

Sorry about the jumps. I've got the organize my posts better. .

[Boli]

Hmmm just had a thought:

I would hate to sleep in a room with an active Dehumidifier, or even work in one with it. Anyone who wanted to install them need to get their head seen to, after ten minutes in there it'll be like a bad hangover.

Any solution should not include a dehumidifier as the human body will complain unless you can find a way to put the moisture back into the air or vent the dry air COMPLETLY out of the room. It won't be nice.

Sometimes people forget when they turn off the heating in the computer room - or vent all the moisture out of the room to "improve their computer" that people have to work in there. (NB: I know turning off your heating is the worst thing you can do in a computer room)

~ Boli

[Groth]

If you've ever worked or slept someplace that was air conditioned, you've already survived a dehumidifier encounter. Ain't nothing wrong with dry air; being in the desert is nothing like a bad hangover.

Turning off the heating is the worst thing you can do in a computer room? Huh. The upper floor of my house is heated solely by computers... :shrug:

[Boli]

Turning off the heating is the worst thing you can do in a computer room? Huh. The upper floor of my house is heated solely by computers...

You either have them on and the heat off... or heating on and them off. It is REALLY bad when you turn them all off go away for a few days and come back and power up directly... this is what my old school did and blew quite a few fuses and a couple of computers, because it was chilly and damp... stupid f***ers.

If you've ever worked or slept someplace that was air conditioned, you've already survived a dehumidifier encounter. Ain't nothing wrong with dry air; being in the desert is nothing like a bad hangover.

Maybe not... but some people are more suseptable to humidity(or absence of) than others. I can't stand dry air myself, still a point worth raising though. (even if it was a bit ranty - apologies to anyone offended.)

~ Boli

[BladeRunner]

Interesting topic, and while I'd admit I don't have more than a passing understanding of all the physics that is involved in the formation of condensation and other atmospheric related things, I understand what I need to do to prevent it forming on my cold blocks and tubes.

A factor not to forget is where I live, (UK), and it rarely gets to 30C let alone above that. Mostly its 20C and 75% of the year that is artificially raised by house heating. Central heating tends to dry out the air a bit raising the due point as well. The chart shows the dew point at the humidity % at a certain temp and like I said it seems accurate to my personal findings using temp and humidity gauges. 100% humidity is very unlikely unless you are in a tropical rain forest although parts of the us can get near 100% I hear? Also rain has little to do with it as It's often high 30% low 40% when its rain in the summer here.

Like said there are so many specific variables to my plan the only way to know if this will work, and how well is to build it, just can't be worked out on paper or via equations at least not to my mind anyway.

I'm the opposite I hate "wet" air and find it uncomfortable when it gets above 60% humidity. We are all different as a girlfriend years ago continually complained of drying out on a trip to the US. The air-conditioning in the malls and cars, (we were in Florida), affected her badly where as I liked it full on ice cold and it didn't appear to dehydrate me, it was an excellent excuse for us to argue and fight, not that she really needed a reason....

[satanicoo]

What about isolating the case, and having an interior radiator cooling the inside air, so the delta between the air and the blocks is low?

[TerraMex]

Er.

( Estás a apanhar do ar .

O Balde (pun) quer um radiador que arrefece o ar a entrar e reduz a humidade relativa porque algum do vapor precipita no radiador (fresco em função da temperatura ambiente). A caixa é isolada, e apenas tem uma saida de ar, a chaminé aquecida que provoca uma subida de ar quente (acima de ambiente) , e cria correntes de convecção que arrastam o ar mais fresco embaixo (que por sua vez já passou pelo radiador e arrefeceu a temperaturas abaixo de ambiente). Menos humidade, menos temperatura, menos propenso a condensações nas tubagens principalmente.

O que estás a querer dizer (que é diferente) é isolar totalmente a caixa do ambiente. E arrefecer o interior. Mas isso não é lá muito prático , especialmente que a quantidade de vapor de água ainda se mantinha no seu interior E para usares um radiador para tal tens de ter movimento de ar, quer seja por ventoinhas quer por convecção. E como usar ventoinhas está fora de questão , fica por criar correntes de convecção que não existem de maneira decente nesse tipo de montagem fechada. Tem de ser aberta. É para isso que se tem a chaminé, forçar movimento de ar com o frio/quente , sem auxilio de ventoinhas.

E se se conseguisse isolar a caixa e ser estanque, podia-se criar um vácuo (e sem ar não há vapor em suspensão, nem condensação). Mas ai é ainda mais chato, especialmente se se quer aceder ao hardware.

A teoria é porreira (e deveria funcionar), na prática nem sei se funciona correctamente. )

[BladeRunner]

Santanicoo

Because that would require a fan, or some way to move the air around, my system has to be totally fanless..... zero fan zone Another possibility is to expand your idea to make the complete case a water box, similar to a central heating boiler. it could then be virtually sealed up and the air inside should remain almost as cool as the blocks / coolant temp...



TerraMex

Can you translate that last reply please

[satanicoo]

Já tinha pensado nisto uma série de vezes, talvez um dia me "passe" e trate do assunto

Ok ok fanless . Just an idea.
The main problem i can think off is the chimney. The "thing that heats the air" would also heat the room, depending on the power of it.

[N8]

Originally Posted by Aardil

I see alot of messages about people wanting chillers for thier PC's.
Most are converting Dehumidifiers or building true Phase change setups.

My random thought is this....
Has anyone ever tried using a old water fountain? You know the kinds made 20 years ago that actually cooled the water.

Again this is just a random thought I figured I would share with you guys. I have no Idea if it would really work but it seems to me It should.

Aardil

I have one of these old fountains that I used to chill my old Celeron 300a and peltier setup. It worked really good, but that probably was less than 100w of heat to deal with.

It actually could get the cpu down to almost freezing, and the water temps were below freezing. I even had to add some automotive antifreeze to keep the water flowing as it would freeze plain water in the water lines. This was probably because they were only 1/4" ID, copper, and I didn't have a very good pump. I bypassed the temperature control switch to make the compressor run all the time.

I didn't get the exterior case, just the guts, so it looks rather ugly. I still have it in storage in case I ever feel like using it again. Pretty damn heavy and awkward. I would need to fabricate an exterior case/covering for it.

[TerraMex]

Can you translate that last reply please

It's just some of the things we've been discussing, but in portuguese , for better understanding by satanicoo.

It's not "something new".

[pelikan]

I am in a similar situation as BladeRunner. My water is chilled to 10-15C by copper pipe in the ground. I get condensation on my blocks if its very humid and I then cook something like soup that adds a lot of moisture to the air (my kitchen/living room is one large room and my computer is there). When this occurs I've been avoiding condensation by opening some windows to vent the steam and cool the room down.
This chimney idea is very interesting to me. Its now one of the solutions that I may try out. I also like the idea of cooling a sealed case with a radiator and fan.
I have been considering raising the temp of my water to ambient by using a valve that would recirculate a portion of the water back through my blocks before it goes through my underground radiator. But its hard to give up the cold water.

Edit: After reading about surlyjoe's project at AOA Forums I'm going with the radiator and fan idea. He put a heater core in front of his intake fan in the lower front of the case. His chilled water passes through that first on the way to the blocks. But I'm going to put the rad after my gpu block for slightly lower block temps and easier plumbing for my particular set up.

[Gooserider]

TerraMex: No , i think you're wrong on several issues.
But i (and Blade does too) do appreciate the input. Let the hostility begin .

fair enough.

Quote: (GR)Your chart describes the dew point, or what temperature condesation will occur at if the air is FULLY SATURATED with moisture.
(TM)If it's fully saturated then it has a relative humidity of 100%. That's the definition of fully saturated.
That's not what the chart means. It means that at a given relative percentagem of humidity, to diferent temperatures, when the condensation will occur. It doesnt have to be fully saturated.

Hmmm, I didn't make myself very clear on that one. I should have said that at the dew point, the air immediately adjacent to the condensor would be saturated, assuming ambient temp and relative humidity as stated in the chart. In essence there is a mini-convection flow, where the air next to the condensor cools to the dew point where it reaches saturation, moisture condenses out and the air flows back into the ambient space, where it warms back up....

Quote: (GR) At least at the temperatures we are talking about (~10-60*C) cold air can hold less water vapour than hot air.
(TM)That's one of the main points. But it's harder for a cold air to release the one it has, if it's a low value of relative humidity, to another cold point (relative cold). The delta T needs a minimum value.

Sort of, but it's not a question of Delta T, but rather that cold air at a low relative humidity(RH) has a lower dew point.

Quote: (GR) Thus if you take a given volume of air, and evaporate a specific amount of water into it, when you heat the air, it's relative humidty will DROP, and so will the dewpoint. If you cool the air, then it's relative humidity goes UP, along with it's dewpoint.

(TM)If you have a given volume of air, with a given percentage of water vapor, if you evaporate an extra quantity of water vapor, then, for the same temperature, it will have a higher dew point. See the chart.

Correct, but not what I said... Assume a box full of dry air (0% RH) Evaporate water into it until saturation is reached. Measure the amount (mass) of water used. The amount of water needed to reach saturation will be a function of temperature, at lower temps less water is needed, at higher temp more water is.

Assume the box has been saturated (100% RH) at 20*C. If the temp is raised to 30*C, (and no more water is added) the relative humidity in the box would be less. If the temp is dropped to 10*C you will get condensation, and the air would still be at 100% RH.

(TM)When you increase the temperature , for the same humidity level the dew point will increase. This goes against what we want.
We want to remove some humidity and maintain a cool temperature. If a good deal will precipitate on the rad, then , the air (still relatively cool) that goes through the case will have less humidity and lower dew point. See the chart. And that's what we want.
But I'm assuming the rad is very efficient on doing that.

Agreed completely, except that I'm not sure the rad would do well enough.

{Cloud physics discussion clipped, IMHO we were both saying the same thing, I just wasn't getting as deep into the details...)

Quote: (GR)
Now as it applies to your design proposal, what you seem to be trying to do as I understand it, is cool the air entering the case, without changing the amount of water vapour that it's carrying other than possibly having some condensation on the incoming air radiator (which really won't help much).

(TM)Cool it and create condensation. Not one or two. Both. Both will change the dew point considerably (Bladerunner hopes). Assuming it can change by a large percentage, both the relative humidity and the temperature. But it's a big IF.

Well, cooling without condensation will RAISE the RH, and bring the dewpoint closer to the temperature of the cooled air. Cooling with condensation will lower the amount of water vapour in the cooled air, but that air will still have a high RH (because of it's low temperature) as long as it isn't warmed back up.

QuoteGR) Assumptions - per your previous posts, and my guestimates...
(TM)Wrong assumptions, assume BladeRunners numbers.
Assume a 20º C ambient , average.
8ºC or less at radiator (or even average 10ºC). No forced air.
The issue is how much the temperature drops as it passes the rad.
And how much a drop of relative humidity.

From one of BR's earlier posts in this thread (highlight added)

BladeRunner:
My system will be cooled by an underground tank the rad will do nothing for the cooling except raise the coolant temp a small amount before it goes back to the tank. At the moment all the blocks in my system add under 1C to the coolant temp in one pass. This might increase to 2C or 3C with Tecs. So if I add this air "conditioner" rad, in the loop, (after its been through the blocks), it will get around 3C warmer coolant than enters the PC, so about 12C is my guess.
The plan is to build an improved underground cooler that will cope with the Tec's and not heat up at all, (probably a large run of copper pipes buried instead of a tank). Assuming I can build a truly effective ground cooler this time, (and It's going to be very large trust me ), then it will return the coolant to the PC completely re-cooled to between 8C to 10C )

Thus, 10*C @blocks, 12*C at rad assuming conservative values for his numbers. (not that it makes a big difference)

Quote:
But wait! you say, wouldn't there also be condensation on the rad?
On the contrary, for me anyway, as stated. You misread. I stated condensation will occur, probably. Again, depends on the rad.

But honestly, if the rad reduced enough the temperature of the rising air, it will be suficient to avoid any type of condensation without tampering with the relative humidity. Given the chart that is.

And you forget that Bladerunner stated that the cooling loop will be cooling pelts, so the water wont be that cold, and the interior wont need very low temps.

My assumption was also that there would be condensation, but that the air coming out of the radiator would be cooled and still have a high RH because of it's low temperature, which would NOT be as low as the cold side of the pelts. Thus the CPU area could still be below the dew point which would not have dropped significantly.

In my proposed modification; which locates the rad > airbox > chimney assembly below the computer box, and supplying the airflow to it; I am assuming that the air would be cooled and condensed by it's passage through the rad, just as you are. I am also assuming some drain or equivalent to get rid of the condensate. But I am suggesting that the air should then pass through the chimney so that it is warmed back up to ambient (or slightly above, but not grossly so - this would need some design tweaking) thus greatly lowering it's RH, and therefore the dewpoint.

This is exactly the same process that a regular de-humidifier uses, except that it eliminates the fans and other motorized bits per the Zero-Fan-Zone spec.

I would be tempted to draw more ASCII art to show what I mean, but the new rev doesn't preserve it properly.

Gooserider

[Grayson]

Hi Guys

Just a quick question to stir things up. What is the Tempeature inside the case now? Is it above ambient? If so the rest of the components are heating the air as it passes through the case. Would this not lower the RH and the Dew Point?

Grayson

[BladeRunner]

At the moment the PC is open and there is some warm up of the air in the pc. This is due mainly to no fans to move the air around, so it stagnates in areas. Natural convection will avoid this getting excessive, but convection requires a differential to work.

With artificial convection currents caused by the chimney effect this slow warm up probably wouldn't occur.

(GR)Well, cooling without condensation will RAISE the RH, and bring the dewpoint closer to the temperature of the cooled air. Cooling with condensation will lower the amount of water vapour in the cooled air, but that air will still have a high RH (because of it's low temperature) as long as it isn't warmed back up.

Sounds good but I really don't think atmospherics are that simple. If that were the case the only way the air could release moisture when it was cooled would be to condensate on everything around it, and that just doesn't happen. At times in the summer here in the uk, (and I use the term summer loosely), we can get big swings between relative humidity and temperature. almost always the humidity % goes down significantly when the temp drops.

Another point to clear up any Tec(s) used will have, and require the cold side to be insulated / isolated. This proposed solution is to prevent condensation on the block surfaces & tubes.

[TerraMex]

Goose, your going well but ... you must drop the "saturated" stuff.
Doesn't exist when talking about atmospheric events. It's a wrong concept.
Confined gases/liquids can be/get saturated. The atmosphere (and including oceans) doesn't, it looses significance when talking about a open system of that magnitude. That's why it's a "relative" humidity.
It all about energy balance and transfer in the natural condensation/evaporation events. It's a constant process.

To give an example , sulphur expelled from a volcano as a vapor sublimates to solid state. The atmosphere wasn't saturated. The super heated vapor just lost energy to the surroundings and the energy balance was altered abruptly to the point it no longer had energy to maintain it's present state. Same goes to water vapor in contact with different surfaces at different temperatures , with different air temperature .

To give another example , in the outskirts of the Sahara Desert, you can have up to 100% RH , and no condensation whatsoever during the day. But in theory, it would be saturated and condensation would be forced (which does not happen). But as night falls, things literally freeze over. Lots of condensation occur (and ice) because of the balance shifted with temperature to the other way, surfaces dropped temperature considerably and energy is removed from the water vapour.

You can have just about any temperature / RH combination. And not have huge amounts of condensation or evaporation (uneven balance).
What changes (and we are discussing) is the Dew Point in those combinations when in contact with a temperature differencial (surfaces or air fronts).
I know it's a tricky subject.

I dont know how to make it more clear, language differences isnt helping either. Maybe it's my fault (probably).

A Dehumidifier re-heates the air to minimize temperature diferentials between the ambient air because it's not his job to maintain cool air. We just want less RH.

Anoher thing you're missing.
The interior of the case is not the main issue. The blocks and the tubes are because they are well below ambient, a few inches can have a delta T of several degrees.
Bladerunner assumes , if he can get the new ground rad, 8 ºC intake, even cooling pelts , it can go up to 12 ºC ... maybe 15 ºC on worse case scenario , not more that that I think. Equal air temperature of air passing (lets say those 15 ºC) and tubes will yeld no condensation because the delta T is minimum , even with high RH (if the radiator forces no condensation). Which if goes according to plan, will. Cool air, less RH, lot less risk. Of course, if things are tweaked properly. May assumptions. You dont need to heat up the air. I dont even think you should. It can shift the balance towards condensation if the delta T is high enough, given the cool surfaces of the blocks/tubes.

If , however, no insulation is used (i strongly advise against it), temps will depend on the cold side of the pelts. Things get even more tricky there. You'll have to know how low can the pelt go when crunching numbers , playing a game, etc. Some degree of control will be necessary, IMO.

Agreed completely, except that I'm not sure the rad would do well enough.

You head him BladeRunner , make it happen .

[Gooserider]

TerraMex, I think we agree on the physics of what is going on, (at least I didn't see anything to argue about in what you wrote) but are approaching the problem from different directions. You are doing a threoretical physics approach, while I am taking a simple language approach.

For instance, I agree that 100% saturation doesn't occur in a natural solution (though it gets close in some places) however it is a good working approximations.

I think my description of what could happen is consistent with what BR describes, including using his own temperature figures taken from his earlier posts (I don't know where you get your numbers from, but they aren't the same.) However I'll admit that it's "guestimation based" rather than on any direct evidence.

TM: Dehumidifier re-heates the air to minimize temperature diferentials between the ambient air because it's not his job to maintain cool air. We just want less RH.

Only partially true. A dehumidifier that didn't rewarm the air would have a very clammy feeling exhaust because the air it output would be colder but still have a very high RH because it was cold. I have experienced this with window AC units in Southern Louisiana - the air coming out is cold, but still so damp that it condenses into fog and feels clammy. (And a few minutes later the cooling coils ice up and freeze solid!)

What I am proposing in effect is to put the computer box at the output end of a fanless dehumidifier. What you and BR are proposing is to put the computer box between the condensor and the rewarmer.

Gooserider

[TerraMex]

including using his own temperature figures taken from his earlier posts

Well, he stated clearly that an achievable scenario for the ground radiador would be 8 ºC (see previous posts). Also that he will be using peltiers. Now depends on the peltiers , but 12º isn't that far off for a heavy pelted WC given his ground radiator. And if the (auto) radiator comes before or after the cooling loop (preferably before to maximize the dehumidifier effect). Lots of If's like i've said before.

but still have a very high RH because it was cold

No, it will have the exact same RH of the heated air IF no condensation/evaporation occurs in the heating element and/or exaust of the Dehumidifier. It has already removed an amout of water from the air, the heater doesn't remove any more (not even it's job). Water vapour doesnt "disappear" with temperature shifts. It has to condensate , or water has to evaporate to change de current RH. Thus de Dehumidifier purpose. If the heating element is shut down, the air will exit cold, but with the same RH, but different dew point.

Same temperature can have a wide range of RH, and vice versa. What acts up on them is the enviorment.

( I'm getting the feeling you're reading the chart wrong, and getting a good deal of ideas from that. You need the RH % AND the temperature of the air in order to read the dew point chart. One without the other doesnt make sense. For all the stated reasons. At a given air temperature, at a given RH % , if the air is in contact with a surface (solid , liquid or gas) with lower temperature, condensation will form. )

What I am proposing in effect is to put the computer box at the output end of a fanless dehumidifier. What you and BR are proposing is to put the computer box between the condensor and the rewarmer

Exactly.
But i already understood that. But again, the difference is the dew point. How cold are the blocks and tubes ? Dunno. One of key issues.
The difference is that BR's rewarmer has no comparison to a rewarmer from the dehumidifier. It's only purpose is to enforce convection currents which won't happen normaly given the cold air at the base. If the cold air isn't forced up (through the case) the system won't work (in BR's idea). Maintain cool air, as blocks and tubes are cool, passing through the case.

[Skoddelos]

I suggest you take a look inside your refrigerator. Hmm, not much condensation at the groceries, right? But in the back you can see some sort of plate with plenty condensed water. The water condeses there because the plate is the coldest place inside the frigde.

If you make relatively air tight case with a small plate or block as the first part of the wc-loop then the same thing will happen. The humidity will condese at the plate instead of the cpu waterblock since the plate is coldest.

I guess somebody could have mentioned this before in the thread but it is only 16 C in appartment right now so it is kind of hard to concentrate.

Btw, I am not dyslectic, just from Norway

[BladeRunner]

That's because the inside of the fridge gets to a preset temp, (around 5C), and so does the air trapped in there, along with the non heat producing food.

The reason you get condensation form ice on the cooling plate part, is because its much lower than the temp of the air and food in the fridge part. The dew point equation has just be moved lower down the temp scale. It's possibly reduced like you say by the fact a fridge is sealed and insulated for greater efficiency.

"If you make relatively air tight case with a small plate or block as the first part of the wc-loop then the same thing will happen. The humidity will condense at the plate instead of the cpu waterblock since the plate is coldest."

Admittedly I haven't got an air tight case, but I just don't think this would happen. You'd get more condensation on a colder part yes... but if other parts were below dew point, they will also form condensation too. I can't see it magically avoid those parts and divert somewhere else because it's colder.

[Skoddelos]

Originally Posted by BladeRunner

Admittedly I haven't got an air tight case, but I just don't think this would happen. You'd get more condensation on a colder part yes... but if other parts were below dew point, they will also form condensation too. I can't see it magically avoid those parts and divert somewhere else because it's colder.

It will work in the long run if you maintain a stable coolant temperature and humidity inside the case.
You were planning to do something like this I assume. This will maintain a rather stable water temp throughout the year. This guy's setup varied 4,3 C over a time of 2 years.

We all agree that the first part of the wc loop (the plate) will be the coldest part and will extract humidity when it's temp goes bellow dew point.

The next step in the loop will not extract any humidity as long as the plate extracts the humidity fast enough to lower the dew point. And that is possible if you have; a slow water temperature change and slow air exchange.

But you must also insulate the case or you will get condensation at its outside.
Therefore it is more common to insulate the tubes and water blocks.

[Gooserider]

TerraMex:
Well, he stated clearly that an achievable scenario for the ground radiador would be 8 ºC (see previous posts). Also that he will be using peltiers. Now depends on the peltiers , but 12º isn't that far off for a heavy pelted WC given his ground radiator. And if the (auto) radiator comes before or after the cooling loop (preferably before to maximize the dehumidifier effect). Lots of If's like i've said before.

The 8*C number was the minimum, with a range of 8-10*C. Since we are talking about Summer humidity, I'm assuming the upper #, but it doesn't matter that much, since changing just shifts all the temps ~ the same amount. Also per BR's spec, the rad comes AFTER the blocks / pelts, which per his temp numbers the blocks will be on average 2-4*C colder than the Rad. (I don't know why we keep arguing about BR's #'s on each post, they don't change... :shrug: )

o, it will have the exact same RH of the heated air IF no condensation/evaporation occurs in the heating element and/or exaust of the Dehumidifier. It has already removed an amout of water from the air, the heater doesn't remove any more (not even it's job). Water vapour doesnt "disappear" with temperature shifts. It has to condensate , or water has to evaporate to change de current RH. Thus de Dehumidifier purpose. If the heating element is shut down, the air will exit cold, but with the same RH, but different dew point.

I agree the water vapour isn't dissapearing, but the air temperature is changing. As I have said before, if one has a box of air at a given temp and RH, then cools the air (but not to the dew point), the RH goes UP. If instead, one heats the box, then the RH goes DOWN

If the air cools to at (or below) the dew point then condensation will occur, but ONLY enough to lower the RH to the point where the dew point of the now cold air is below the ambient temp, but the RH of the cooled air is going to be effectively saturated so long as it is cooled.

One of my key assumptions is that the air coming through the rad will be cooled to something close to the rad temperature since the airflow will be low. (If the airflow were higher, then you would still have condensation on the rad, but not as much air temp change so more dehumidification effect would be occurring) I also make the assumption that the air temp will not change significantly between the rad area and the block area.

If the air coming through the rad is close to the rad temp, then it will have a high RH for air of that temperature. When that already cold, humid air hits the slightly lower temp blocks, then the blocks might be just enough colder for ADDITIONAL condensation to occur.

But i already understood that. But again, the difference is the dew point. How cold are the blocks and tubes ? Dunno. One of key issues.

I agree it's a key issue. If they are above the dewpoint of the cold moist air coming off the rad, then there is no problem. If they are below, then there is a problem. My opinion is that since per BR's spec, they SHOULD be colder than the rad, the risk is considerable.

The difference is that BR's rewarmer has no comparison to a rewarmer from the dehumidifier. It's only purpose is to enforce convection currents which won't happen normaly given the cold air at the base. If the

In the design as BR proposes, I agree, the rewarmer doesn't do anything to the RH in the computer chamber, which I see as a problem.

In my proposed alternative, the rewarmer still drives the convection currents, it just now ALSO serves to effectively lower the RH (and thus the dewpoint), hopefully enough to the point where further condensation on the cold blocks will not occur.

---------------------------------------------

Skoddelos:
I suggest you take a look inside your refrigerator. Hmm, not much condensation at the groceries, right? But in the back you can see some sort of plate with plenty condensed water. The water condeses there because the plate is the coldest place inside the frigde.

Actually Skoddelos, if the air is humid enough, you WILL initially get condensation on all the stuff in the fridge, especially if it isn't a self defrost model.

After that, you have a semi-sealed box, where the water vapour condensing on the plate is effectively removed, lowering the RH of the air in the fridge below the dewpoint of the groceries, but not that of the plate. Since it's now drier, the water that was condensed on the groceries will evaporate back into the air, leaving just what condensed on the plate.

Gooserider