[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.