Compressor Question - How to put together best system

Bruce Griffing · Jul 17, 2012

I have a compressor in the attic of my shop here in Texas. It gets really hot up there. Recently, the compressor motor started to cut out thermally during heavy use. It is OK after it cools, but it is old and I want a new system. My plan is to relocate the new compressor outside the shop next to the shop A/C unit. I use air at about 100psi with max usage presently at 10cfm - the capacity of my present compressor. My usage is far from continuous - some days the compressor is not used at all. I would like to go up to about 15cfm in the next unit. My ideal unit is this - a prepackaged unit that includes compressor, receiver, trap and drier. It would be set up for outdoor use and run on single phase juice. No surprise, but I have not found anything like that yet. I realize I could put the parts together myself and build a little house around them, but I would rather buy complete if possible. How close can I come to my ideal system? Suggestions?

JRIowa · Jul 17, 2012

That's only about a 5hp compressor. That's small in the compressor world. IR sells an intregal system that includes the dryer. A 5hp unit will flow about 20 cfm. You're probably looking at $7-8K plus a doghouse.

Your cheapest solution would be to get a larger recip compressor and put outside. Then, have a dryer inside.

You might check with McKenzie in Waco and see what they have in new or used.
JR

Shawn Ghormley · Jul 17, 2012

The smaller screw compressors (7.5hp) include a dryer, but I think you'll still want it in a shed type building/lean to. These packages are also $$$$. I'd look for the compressor you want and add the dryer.

Bruce Griffing · Jul 17, 2012

JR - I was thinking of putting the dryer outside because the heat load would otherwise have to be taken up by the shop A/C. It seemed more efficient to send the heat outside in one step rather than two. But maybe the drier would not work well in the summer heat. It seems to me that there would be a market for such a unit - but nobody seems to make one.

ford 460 · Jul 17, 2012

I dont know if im missing somthing hear but it sounds like you just need a 5hp 2 stage compressor nothing fancy for the amout of air your using look for a 80 gal tank little more time between run. And with locating it out side youl need to run a 1" or so steel air line in to the biulding sloping it back to the compressor tank to help control moisture. This should help cool your air just fine for the cfm your talking about using. I personally would stay away from IR when looking for a compressor look for one were the pump runs at 800rpm or less this = quiter cooler and longer lasting you should be able to do this for 1500-2000$

JRIowa · Jul 17, 2012

Bruce,

That type of unit is made, just not that small and not single phase. I've seen 150 hp units up here that have all that plus heated moisture traps for our winters. The location of the dryer is up to you. I like to see them close to an outside wall so that the hot air can be vented outside. For one the size that you're looking at, I'd mount about 5' off the floor (or higher). That way the dryer removes the hot air close to the ceiling and gives a littel air flow. Put a damper on the discharge and route the heated air inside for the winter.
JR

FredC · Jul 17, 2012

I am with Ford 460 on this, 5 hp 2 stage will be more than enough. You can still do some growing and you will be covered. We are using a Champion unit for about that money. We installed an aftermarket cooler and fan between the compressor and tank. The air comes out of the cooler at ambient and a seperator catches a lot of water at that point. Atlas has a manual on selecting a compressor it might be appopriate for larger air demand. I am not sure if I can post it here as it is in PDF.

Shawn Ghormley · Jul 17, 2012

Are you looking at a new or used compressor?

S_W_Bausch · Jul 17, 2012

You might want to consider a fresh air intake for that unit.

Sucking hot (expanded) air isn't efficient.

Providing cool air for intake and motor cooling would be a good start.

Bruce Griffing · Jul 17, 2012

SW
We don't have cool air in Texas this time of year - just hot and hotter. But I do get your point - intake from outside the attic would be an improvement over what I have now.

Fred and Ford
As for the one or two stage question, I don't believe in compressing air to a much higher pressure than the use pressure, as all of the energy used in doing so is wasted. I know many folks don't buy that argument, but I do. So if the new compressor is a recip, it will be one stage. A two stage would be fine if the compression ratios added up to say 120psi output, but that is not generally the case.

My shop is a 1100 ft2 addition to my house - located in the middle of a suburb. I keep a low profile and nobody complains. The shop is constructed with brick over frame like the house, and does not look like a shop at all. To an outsider it is just part of the house. That is part of the reason I was hoping for a packaged unit. Something that might be sort of boxy looking and not obviously a compressor. Like some of the rotary vane units I have seen in Europe. I realize I could do a construction project around anything I put in, but that will add time and cost and it will be hard to make it look good.

JR-
I did call IR and they sent me a quote, but it is just a bunch of parts, not a packaged unit. I will call them again tomorrow.

ford 460 · Jul 18, 2012

a 2 stage pump is more efficient then a single stage. and if you dont want to run to 175 psi thers no resson why you cant turn it down to 125 psi or what ever you want its only a mater of the pressure switch. And to run at 175 psi is not wasted inless your leaking all the air out. It just gives more capacity.

Bruce Griffing · Jul 18, 2012

Ford-
A two stage compressor is more efficient that a single stage compressor if both compressors are producing air at the same pressure. The degree to which this is true depends on how much the air is cooled between stages (intercooler), plus other basic mechanical efficiencies. So I do agree with your statement that two stage is more efficient than single stage (at the same pressure). That said, if the use pressure is significantly lower than the ultimate pressure of the two stage compressor, the gains in efficiency are lost in the free expansion of the air at the tank and regulator. As a practical matter, that means that a two stage compressor has higher system efficiency down to some use pressure, below which a single stage is more efficient. So the key question is what is that cross over pressure? That depends on the details of the two compressors that are being compared. One rough but easy check is to compare the air delivery at the use pressure. For example, I compared Jenny 5hp single and two stage compressors - I chose these because I could easily find the specs. For 90psi air delivery, the two stage compressor (GT5B-60V) is rated at 18.3cfm and the single stage compressor (j5A-80V) is rated at 28.7cfm. Since both compressors use 5hp motors, the single stage compressor is clearly more efficient at 90psi use pressure.

ford 460 · Jul 18, 2012

I dont want to argue I see you want a single stage pump go for it at the end off the day its your money and you have to live with it. I not a physics scholar buy any means but I still fill a two stage is a better choice and more capacity. And for your jenny comparison I dont agree I can read those numbers to. The GTs 18.3 cfm is actualy at 175 psi and the J pump is right at 28.7 cfm @125. Now for what your missing is your not comparing apples to apples the single stage J pump has a bore of 2.5"x3.25" stroke x 4 being this is a v4 pump. The GT 2 stage pump has the same 2.5" bore but only a 2.375 stroke with only 3 clyinder drawing in air and the 4th being the high pressure cylinder. So the single stage should put out more in this case being its a biger pump and has one extra cylinder to draw air in and it has a 7/8" longer stroke. And then ther the deference in rpm.

I will say if you are lookin at Jenny compressors they are a great compressor and would be one of my first choices. I have Emglos (same as Jennys) a 3hp 8g tank with g pump I also have a 5hp W pump in my shop witch is basicly the same as the GT thes are very smoth and quite compressors. I also have a 10hp Ir in the shop . And I also have a couple Rol Airs ther a great compressor they like to use a larger pump and run it slower. I have a 8hp gas with 2stage pump and a 5hp electric 2stage pump both have 8gallon tanks and shut of @135psi.

All brands list diferent specs I like compressors that use slow turning pumps and of the shelf conponents. And motors like baldor,Lesson. if you look IRs dont fit in this catagory

robmc · Jul 18, 2012

Bruce Griffing said:
Ford-
A two stage compressor is more efficient that a single stage compressor if both compressors are producing air at the same pressure. The degree to which this is true depends on how much the air is cooled between stages (intercooler), plus other basic mechanical efficiencies. So I do agree with your statement that two stage is more efficient than single stage (at the same pressure). That said, if the use pressure is significantly lower than the ultimate pressure of the two stage compressor, the gains in efficiency are lost in the free expansion of the air at the tank and regulator. As a practical matter, that means that a two stage compressor has higher system efficiency down to some use pressure, below which a single stage is more efficient. So the key question is what is that cross over pressure? That depends on the details of the two compressors that are being compared. One rough but easy check is to compare the air delivery at the use pressure. For example, I compared Jenny 5hp single and two stage compressors - I chose these because I could easily find the specs. For 90psi air delivery, the two stage compressor (GT5B-60V) is rated at 18.3cfm and the single stage compressor (j5A-80V) is rated at 28.7cfm. Since both compressors use 5hp motors, the single stage compressor is clearly more efficient at 90psi use pressure.

You raise some interesting questions and I'm not sure what the answers are but would like to know. You compare the single and two stage jennys but I think you've got apples and oranges. The bore and stroke would seem to put the w series (two) as a comparison for the gt (single) and then you have to take into consideration the rpm of the pumps. That 28.7 cfm isn't delivered air which is 19.0 (single) vs. 17.5 (two stage) and slightly lower rpm w5b-80 ( two stage pump). These I believe are the numbers that count. You said a two stage is more efficient if both are producing at the same pressure. If you put a smaller pulley on the two stage electric motor or use a VFD to slow it down to equal the 90 psi use pressure of the single..... say about 125 cfm (and I agree that most people regulate down to 90-100 psi use pressure) is the double more efficient? Not trying to be a bb'ster because I honestly don't know and am glad you brought it up. Some of the answers about where to place the inlets and outlets for air are interesting and make sense. I think you can put together just what you want but whether in one package...... not sure. The small rotary screws (5hp) are close and maybe $5000.00 with a dryer but I would almost think your original thought of a reciprocating is the way to go for the usage you plan on, anyway good luck.

Bruce Griffing · Jul 18, 2012

Ford-
I looked at the specs for the Jenny compressors for air delivered at 90 psi. So those numbers are specs given by Jenny for 90psi delivery for both the two stage and the single stage.

Here is a link: check the specs tab

GT5B-60V Jenny 5-HP 60-Gallon Two-Stage Air Compressor (230V 1-Phase)

robmc · Jul 18, 2012

ford 460 said:
I dont want to argue I see you want a single stage pump go for it at the end off the day its your money and you have to live with it. I not a physics scholar buy any means but I still fill a two stage is a better choice and more capacity. And for your jenny comparison I dont agree I can read those numbers to. The GTs 18.3 cfm is actualy at 175 psi and the J pump is right at 28.7 cfm @125. Now for what your missing is your not comparing apples to apples the single stage J pump has a bore of 2.5"x3.25" stroke x 4 being this is a v4 pump. The GT 2 stage pump has the same 2.5" bore but only a 2.375 stroke with only 3 clyinder drawing in air and the 4th being the high pressure cylinder. So the single stage should put out more in this case being its a biger pump and has one extra cylinder to draw air in and it has a 7/8" longer stroke. And then ther the deference in rpm.

I will say if you are lookin at Jenny compressors they are a great compressor and would be one of my first choices. I have Emglos (same as Jennys) a 3hp 8g tank with g pump I also have a 5hp W pump in my shop witch is basicly the same as the GT thes are very smoth and quite compressors. I also have a 10hp Ir in the shop . And I also have a couple Rol Airs ther a great compressor they like to use a larger pump and run it slower. I have a 8hp gas with 2stage pump and a 5hp electric 2stage pump both have 8gallon tanks and shut of @135psi.

All brands list diferent specs I like compressors that use slow turning pumps and of the shelf conponents. And motors like baldor,Lesson. if you look IRs dont fit in this catagory

Ford you beat me to it...... if I had read yours I wouldn't have posted!

Bruce Griffing · Jul 18, 2012

For me the bottom line is this - I spend the electricity for a 5hp motor and I either get 18.3 cfm at 90psi or 28.7cfm at 90psi. So which is more efficient?

ford 460 · Jul 18, 2012

I dont know how to post the jenny site but it list the GT pump at 18cfm @175psi so im not sure witch is right. Never mind witch one you get I will stad and say a jenny / emglo are great compressors. As I stated I own a few compressors and Iv been around alot more and the Emglo are the smothest and very quite and still biult out of cast iron here in the Us. They must be doing somthing right since the other companys you find in box stores try to copy them .

PeteM · Jul 18, 2012

Bruce Griffing said:
For me the bottom line is this - I spend the electricity for a 5hp motor and I either get 18.3 cfm at 90psi or 28.7cfm at 90psi. So which is more efficient?

Note that you'll get more air out of a tank that's at 175 psi if you draw it down at 90 psi. So, the difference is not so great as you might think. That said, if you're never going to use more than 90 psi, the single stage unit will likely be more efficient. Personally, I'd want a compressor that would be happy delivering 120, 130 or more psi when it's needed. Sometimes 90 psi isn't quite enough to get a air nailer through hardwood or an impact gun to take off a frozen nut.

As for the package deal, you'll spend more time looking (and thousands $$$) more trying to find the perfect all-in-one. And when either the air pump, motor, refrigeration pump, or refrig. motor go out you'll spend more to fix them. It's pretty simple to buy a decent 5hp compressor (Quincy is decent quality, fairly priced) and put it outside. Put the drier inside or out based on convenience.

FWIW, I had an Emglo 3hp that delivered something like 13+ CFM at 90 psi. It worked fine. Now have a Quincy 5hp. It works even better though still just a bit marginal for sand blasting. Another "5hp" mythically rated Craftsman compressor in parallel provides a bit of extra oomph when needed.

In our temperate climate, a 100' long run of zig zagged 3/4" copper on a cool basement wall cools things down well enough instead of a drier for all but plasma cutting and spray painting. For that, conventional water separators plus a Motor Guard filter does the trick. The drier probably makes sense where you are.

robmc · Jul 18, 2012

Bruce Griffing said:
For me the bottom line is this - I spend the electricity for a 5hp motor and I either get 18.3 cfm at 90psi or 28.7cfm at 90psi. So which is more efficient?

I see exactly what your saying from that spec. tab from Air Compressors Direct but something seems to be wrong. I don't think that 28.7 figure is right. Maybe I'm wrong but I still think the delivered air on that setup is about 19. The cfm and acfm and scfm, etc.,etc. gets all mixed up sometimes. The actual delivered air is not what's being shown, I don't believe. It would paint a totally different picture if the actual delivered air from a comparable 1 and 2 stage at say 125 psi could be shown and I think it can if you dig through the actual Jenny site, forget about the Air compressors Direct site for now and I think you will understand.

Compressor Question - How to put together best system

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