Best place to run first stage compressor for Shoebox?

[Franklink]

I've been eyeing the Shoebox since the price drop and finally ordered one a few days ago.

Is it better to run the first stage compressor in my cool garage or in my climate controlled house?

The garage is attached, but not insulated, nor heated/cooled. The garage is basically hot in the summer, cool in the winter.

I live at pretty high altitude and only have about two months of the year where the climate is hot enough that the garage doesn't cool off at night. The other ten months of the year, the garage is either fairly cool or cools off each night.

The interior of the house is air conditioner cooled and wood stove heated.

I have some conflicting thoughts on this. First, the wood stove drops the humidity, but the cooler air in the garage is supposedly easier to get the water to condense out of?

I'm going to use the Wilkerson dessicant bead filter on the low side and I bought a cheap, small volume tampon filter for the high side for about $20. The plan is to see if that tampon filter gets wet, if it does, then I'll pony up for a more expensive high side filter. I also plan on using 25ft of low pressure hose between the first stage compressor and the Shoebox, with the Wilkerson next the the Shoebox.  I'm kinda considering running everything in the garage, with the 25ft of hose zigzagged between some nails in studs 6 or so feet apart to see if gravity can help condense water back into the tank on the first stage compressor. I've also thought of running the first stage in the garage and putting the compressor hose through the wall to feed the Shoebox inside since my gun-room shares a wall with the garage (probably the hardest sell with the wife since the "gun-room" is also our SHARED walk-in closet).

Just doing it all out in the garage would be the most convenient due to noise and my wife's preference. But I can convince her otherwise if the garage means more moisture in my tanks/guns.

Obviously, the goal here is the most dry air possible. I'd like to keep the dessicant drying in the oven process to a minimum too.

(This question is for the 10 months of the year that the garage is either cool, or cools down at night. The two hot months (which are also the high humidity "monsoon season") I plan on filling inside the house where the central AC is keeping the moisture level lower than outside.)

[AlanMcD]

The best answer for the Shoebox is to run the shop compressor wherever the temperature is lowest, so the shop compressor tank can cool down the most.  Ambient humidity is irrelevant.  This is because you want as much vapor as possible to condense out of the air in the first stage, and that will occur where the tank is at it's lowest temperature.  Even very low ambient air humidity levels will have saturated air when compressed to ~100 psi and then cooled back to ambient.

And of course the best answer for you is to keep your wife happy.  Fortunately, both answers are the same!

[FuzzyGrub]

In AZ, there might not be as big of difference, but currently my indoor humidity is 45%, but outside/garage is 84%.  As long as I have had a SB, it has been inside.  It is paired with a nice quiet CAT primary compressor. 

[AlanMcD]

Here is why I said the incoming relative humidity really does not matter:

In another post, I showed the different dewpoints and absolute humidity levels for various pressures in an attachment.  In that table, I picked 68 degrees Fahrenheit.  I will build on that a bit here . . .

If we compress air to 100 psi, and allow the tank to cool back down to 68F after compression (and we will assume we still have 100 psi at this point), the most water vapor that the air could hold would have an equivalent dew point of 17F if allowed to expand back to ambient pressure (that was all in the table).  But if we look at ambient pressure air at 68F that has a dew point of 17F, then we are looking at air that has a relative humidity of only 14%!  Said another way, the only way that the shop compressor's tank won't have any liquid water in it from condensation would be if the ambient air used for compression had an RH no higher than 14%  at 68F . . . .

I expect that unless you live in a true desert (like the Sahara), any air you run into your shop compressor will result in having condensation form in the shop compressors tank.  The only question is how much liquid water condenses, and thus how often you need to vent it out.  Either way, you are still going to have to vent it out at some point.  The best result for your desiccant air drier in front of a Shoebox is to have that air in the shop compressor's tank get as cool as possible, so that as much vapor can condense out as possible.  Personally, I would prefer to vent my shop compressor more often that having to regenerate my desiccant beads. And the reality is that if you use your shop compressor much, you should be venting fairly regularly anyways, so there really is not much difference on that end.

[Franklink]

Thanks. That's the kind of info I was looking for.

As a somewhat related side note: current humidity is 30% and the lowest I saw today was 19% at around 2pm. That's pretty typical for us unless we've seen some precipitation in the last few days. Sounds like the garage is where the compressed air magic is gonna happen (for everything but monsoon season when it's hot and humid).

Thanks again.

[FuzzyGrub]

FWIW, I have yet to trap any moisture in my HP side filter.  70 F inside vs cold or hot outside?  Make your choice.  I only see that low of humidity in the middle of the winter.  You will be fine with whichever you chose.

[AlanMcD]

I will admit that 19% humidity is lower than I expected, but you also said that was at 2 PM . . . . so it was probably a good bit warmer than 68F, so the air could hold a lot more water then to start with (and thus 19% of a bigger number is even more vapor than 14% of a smaller number).

The problem with speaking in terms of relative humidity is that it is exactly that - it is all relative.  In other words, you need at least two data points and then calculations to know how much water vapor is actually in a given unit of air.  That is why when doing all the calculations for figuring out what I was going to do for my set up I used absolute humidity values.  That let me determine the ccs of water involved and calculate what I should expect to have happen.

Then I went ahead and built my filter system, used it, and verified the results: a large silica desiccant filter (leading to long dwell times for the air in the filter) fed with air from a shop compressor cooled to ambient (~70F or less) conditions will remove all the water vapor needed to prevent condensation from happening in a tank stored and used at ambient conditions (colder use, like outdoors in the winter, would likely lead to some condensation, but that would likely evaporate when the tank warms back up).

Here are the key results:
1) I inspected my guppy tank after compressing about 500 cubic feet of air into / through it, and I found no signs at all of any water condensation.
2) I dried my silica beads and the reduction in weight after drying yielded an absorption rate of ~2.2 grams per cubic meter of air passed through the filter, which was right at what I calculated it should be (based on the average air that I was feeding it).

Bottom line, you will be fine!