Mine is bigger than yours: Shop A/C notes

"Proctologically Violated©®" wrote in message news:RZDti.1$ snipped-for-privacy@newsfe12.lga...

Proper dehumdification with an AC unit hinges critically on the size of the unit vs. the required size -- i.e. heat gain of the structure.

An AC system dehumidifies effectively only when it runs long enough to condense the moisture. An oversized unit will not run with a high enough duty cycle to do the job. If undersized, of course, it runs too much. Peak periods with a properly sized unit will probably see the AC on about 70% of the time.

The dew point in a properly conditioned area will always be well below the air temperature, so it's not a worry. However, equipment near a frequently used entrance or leaky window may condense.

Most shops down hear in the Sayouth keep their air fairly warm, but nicely dry. At 78F, you still feel comfortably cool if the RH in the room is low enough, and the air is kept moving.

BTW... fans in a shop are a good idea. Especially if you're on a slab, the relative humidity will be higher in some zones than others. Keeping the air moving helps the AC remove the moisture evenly.

LLoyd

"Proctologically Violated©®" wrote in news:RZDti.1$ snipped-for-privacy@newsfe12.lga:

Keep in mind that the "standard" temperature for measurements is 68°F. Course, if your tightest tolerance is +/-0.02" then the temp won't matter too much if you run to the center of tolerance. If you do any tight tolerance work though, you'll need to do a temperature correllation and adjustment based on the actual shop temperature and material being used.

So what should the temperature and humidity be in a shop?

How about in the house?

Whatever is comfortable for you, and with the dewpoint well below the temp. It's really a matter of personal preferance.

I keep mine at about 78F with an RH of around 60%.

LLoyd

I don't know what kind of lighting you have, but flourescent lights are a lot more efficient. Even if you have flourescent lights, it might be worthwhile to switch to T8 lamps.

At this time of the year, you might also be able to find some sales on high efficiency air conditioners. A relatively small one that would run nearly continuously ought to let you just run the air conditioner without running the dehumidifier. Neither of these things will help your short term cash flow, but will help in the longer run.

=20 Dan

The measuring instruments are also calibrated for 68°F. If everything is the same material as the mikes and you keep your hot little hands off the metal part of the mikes there wont be too much of a problem.

John

It was stated hereabouts (or mebbe alt.home.repair) and with some authority that 40% humidity is the lowest you should go, but which is about right, as well. Forgot the reasoning, but might have had sumpn to do with static electricity. Whatever it was, it sounded good, so I keep the humidifier at 40% and hope to god the digital readout actually means something.

I don't know what kind of lighting you have, but flourescent lights are a lot more efficient. Even if you have flourescent lights, it might be worthwhile to switch to T8 lamps.

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I have both T12 and T8, the T8's accumulating as HD has the 4-footers for $7. But they charge over $6 for the g-d bulbs--2 pak. Can get'em for about $1-$1.50 each at Sam's, iirc, in 10 paks. Soft/warm whites are much more, tho.

These fixtures as a whole are rated at 2x40 (T12), or 2x32(T8), but I'm betting the whole thing is closer to 100 W. Hopefully the lumen output is much greater than the same wattage incandescant--would be inneresting to know the actual comparison. ========================

At this time of the year, you might also be able to find some sales on high efficiency air conditioners. A relatively small one that would run nearly continuously ought to let you just run the air conditioner without running the dehumidifier. Neither of these things will help your short term cash flow, but will help in the longer run. ==========================

That's actually an excellent idea. Clearly without heating up the place, nor cooling it down too much. However, I am sort of condemned to an Amana portable, which I think only puts out about 7K, and that's probably optimistic. I think the smallest window unit, which I couldn't use anyway, would be about 6K. I believe the Sam's club dehumidifiers, about 600 W, are equiv to about a

4-5K A/C. But your point, in a bigger shop, seems to be on the money. AND, you get boucou "free" and perty pure water.

As it is turning out, the shop is cool-er to begin with, and even with the dehumidifier going, I don't think the A/C kicks in.

I was going to go with a mini-split (esp now that I've got a punched hole through the 2-foot foundation wall for the amana hose--wow....), but if the crappy portable is doing the job to excess, imagine what a mini-split would do! In fact, I installed the Amana as a sort of trial run, and was very surprised.

How crappy is the Amana? So much so, the PC Richards guy was discouraging me from buying it! No power, he said. But, so far it hasn't broken (second year, heavy use up until now), and the chinese quality on these things at least does not have me gnashing my teeth. And it did the job! Also, it can spit out the condensate with the hot air, if you choose. Really pretty neat, AND I think this increases efficiency, somewhat.

Anthony:

I was doing some 132" long aluminum aircraft seat mounting rails for Boeing about 10 years ago. Our shop air conditioning temp. is normally set to 78 degrees. The parts had lots of holes (whose location was + or

- .005 from one end), and other misc. features. They were done in a Fadal with 40" X travel with both end door removed, and they were advanced by putting one of the prior drilled & endmill bored holes on a fixture pin. Any length errors would probably accumulate. The bottom line was that I looked in Machinery's Handbook for the coefficient of linear expansion for 6061 and adjusted my geometry and toolpaths by the amount for 10 degrees difference. (I remember it being something like 1/2 a thou for every 4 or 5 inches or something - I could be off though it's pretty fuzzy after all this time). I did a test piece and sent it to be checked with the subcontractor's CMM, and it came back OK, so we did the whole run. We warmed the machine up and ran the coolant till it was close to the 78 degree shop temp. before running parts.

Was that 10 F difference for the 68 to 78 degree difference?

It seems to me that you would have to account for expansion differences only if the machining was done at a temperature different than that for the

*intended use of the part*.

Oh, I get it: They proly spec'd it at 68 deg and were then going to inspect it at 68 deg. Then the ultimate usage/temperature part is *their* problem. Which makes sense.

The idea, of course, is that you inspect all of the mating parts in an assembly at a specific temperature. Differences in coefficients of expansion aside - something that does have to be accounted for in many cases - the parts will be at the same temp. at assembly. I'm sure you have heard of "Standard Temerrature and Pressure" in your wanderings

Hey, PV = nRT'n'shit. (T in deg Kelvin) About the only practical use I ever made out of that goddamm formula is to figger out that yer tires' psi increase by about 10% at road speed. On the order of 3-4 psi. And, I proly got DAT wrong.... :) Never did get around to actually *checking* it empirically! Would be interesting to see what the diffs actually are in winter and summer.

Also, there are all kinds of g-d coefficients of expansion: volume, linear, cupla others.

Man, if I had to account for g-d expansion in my shit, I'd go into an epileptic fit.

As opposed to your normal state? How would we be able to tell the difference? LOL

J

Put the aluminum into a freezer for 24 hours before you machine it.

John

Woops I missed something, run it dry no coolant.

John

Guminess is due static cohesion, so you might need electricity to cause that. What happens here, that aluminum gums up is something similar to induction between two molecules, the valence exchanges one electron with to its neighbor, however, aluminum always has one floating around that's why it attracts another from its neighbor so it doesn't know the difference between neighbor and itself, so what you get is a strong non-conductive static bind which can cause gum build-up.

John

PV:

68 degrees F (20 C), has been the standard temperature for measuring industrial parts since the 1930's. Here is a site for a little article (well actually fairly long), on the history of the choice of 68 F (20 C) for measuring manufactured parts.

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While most dimensional metrologists know that the reference temperature for dimensional measurements is 20 °C, very few know how or why that temperature was chosen. Many people have thought it was, in some sense, arbitrary. In actuality, the decision was the result of 20 years of thought, discussion, and negotiations that resulted in the International Committee for Weights and Measures (CIPM) unanimous adoption of 20 °C as the reference temperature on April 15, 1931. =====================================================================

I find that my 8,000 btu unit keeps my shed/shop (8X12) at 75 degrees and the humidity runs at around 50-70% RH (got a hygrometer out there ...) . I only run it evenings and weekends , but have had no problems with rust ... and the energy bill isn't all that bad . I suspect the lathe pulls more . You do realize that the A/C is taking moisture out of the air too ? That's the biggest reason I installed mine (yeah , right , I lie about other things too) .