the project you are trying to do is not be an easy task as it would look like. First you need a model that can handle the problem in a good way. Due to the fact that you have air / water this would more or less lead to multiphase solvers (that is always expensive). Further more, as you can imagine, the water you could get due to the condensation is more or less - not a big amount, isn’t it (some droplets in a few minutes / hours?). I am sorry but I do not have any idea about the volume fluxes of air and water in that kind of geometries.
Further more you have a separation of humidity air to dry air that will form droplets in the pipes. You see that I can even bring more and more aspects to the simulation. I think the main challenge is to figure out the correct model but as far as I know, FOAM will not offer you a model that will directly handle the stuff you want.
Other topics would be - meshing etc.
What you need would be a solver that includes the enthalpy equation and hence a temperature depended solubility of water in air and a two phase model (water and air). The VOF method would be the wrong approach. Maybe some Euler-Euler approach. If the pipe diameter compared to the length is in a special ratio, I would neglect at the beginning.
In my opinion the critical thing is meshing here (it is definitely not a big deal to mesh something like that, but the amount of cells you get is important).
Hope I could help you a bit