Relationship of Air Velocity-->cfm///Air Compressor Buyers Guide

The bells and whistles some are extras some are standard. I Recently bought variable screw compressor. What one manufacture offered as standard controls. The others listed them as extras. Which would have push the cost up another couple of grand.

Construction the oil sump in the manufactures compressor that I bought was approximately three times the size as the other manufactures. Which aids the compressor in running cooler. Increasing the life I hope.

You all so need to consider your usage. A variable screw aids in only producing air at the volume of your usage reducing electrical cost. In my choice of size bought one with twice the capacity as needed. As the business expands will not have to add additional compressor.

Pressure, volume and usage are the three main factors the you need to know in order to select a properly sized compressor.

Pressure: this is the minimum that your requires to operate. If you have two AOD pumps and one requires 50psi and the other requires 90psi, your plant minimum would be 90psi.

Volume: the max demand is the total CFM usage through out the faciclity.

Usage: is based on frequency, If you use 100 cfm continuously with peaks up to 200 for short durations you may want to consider a 150cfm unit but a larger receiver.

Anyways find out how much air you use and when you use it then you will be able work with your reps and get the right compressor.

hi guys.thanks for the reply.regarding the explaination by Richard L,in the usage part..i dont understand what you are trying to say.what is the connection between the sizing in cfm and a larger air receiver?supposed that a production site in a certain company uses the compressed air continuously for around four hours,rest about 30 minutes and continue the usage again,what would be the proper sizing and receiver arrangements?will energy be saved by using a compressor with VSD?

We do what's called "plant air & energy usage audits" for our customers- when they have questions like yours.

An audit will tell you exactly how much cfm you are using (demand), how much kW of electricity you are using to produce that air (cost) and what your actual 'system' pressure is (not the pressure that the compressor is using to send your air out into the plant).

As the data is logged 1/sec for approximately 7 days, you will also be able to see how demand varies throughout your production day and what you are paying to produce it. In addition, you will also be able to see what your plant's "leak load" is.

For instance- If your demand is fairly constant, a properly sized load/unload compressor is most efficient. If your demand varies enough on an hourly/daily/weekly basis, or your demand will increase in the future, a VSD will most likely save you a lot of money. Average energy savings of VSD as compared to standard compressors = 35% when properly sized.

A real audit is the only intelligent way to start consulting you on what you really need!

In Wisconsin, our electricity provider even subsidizes these studies if there is a charge, due to their relevance. (In most cases, you can get them done for free, or close to it!)

Air compressors account for about 10% of the energy bill for U.S. American Industry. As most systems' efficiencey can be improved by over 30%, we can all take part in improving our electric bill as well as the environment, by having our system audited. Remember, a professional compressor dealer should have already provided this service to you!

Richard provided excellent information! The only thing I might add is a demand side regulator on the usage side of the receiver. You can purchase a 2" for under $1,000 and it can increase efficiency by decreasing artificial demand, by up to 18%.

Also, reps may or may not help! I met a guy yesterday who's 20hp load/unload rotary screw had been meeting his demands for over 10years. ONCE in the last 2 years, did he not have enough air.

A rep told him that his 20hp machine wore out because it had been working too hard. They brought in a 15hp rotary screw for rental while they "fixed" his unit. The 15hp machine is meeting his demands- no problems.

Meanwhile, they quoted him a 40 & 50hp rotary screw load/unload machine!

1st- Rotary Screw Load/Unload machines are designed to run most efficiently @ 100% x 24/7

2nd- His air usage demands vary on a daily basis

3rd- If you are upsizing this particular case to account for the "once off" lack of air and potential growth in the coming years- A 30hp VSD will provide him with app. 40% growth potential while saving him about $2,500/year compared to a 20hp load/unload and about $3,500/year compared to an oversized 50hp load/unload!

These numbers can vary greatly, depending on each different facilities' needs.

LESSON LEARNED- Atlas Copco, Sull-Air, Gardner Denver and Ingersoll Rand all make good industrial machines. (Size-for-Size, I have pretty much listed them in the order of their energy efficiency. Check the CAGI Data Sheets) A good dealer who actually understands how to consult you, can save HUNDREDS of $'s- more than a good compressor.

As stated by danek, a complete audit of your installation and your needs is the best way to determine what you need. In making your final decision, there are parameters that will be unique to your situation that you will use to make the final determination. As it relates to the advertising that you see, I would advise taking it at its face value. That will be clear in a moment.

After you have received the results of your plant audit, you will probably be given several options. Here is where you must make decisions that are yours alone to make. The audit will tell you what will work, what will work the most efficiently, what will work the most economically and the differences between them. The most expensive system may be the very best for you, but may be beyond the scope of your budget. Conversely, the least expensive unit may not be as efficient. It may take more energy to operate. It may be labor intense, requiring more manhours of maintenance. And there are probably other options that lie somewhere in between those options.

You will choose the one best for your installation. But price and efficiency being considered, there is another consaideration that is important. That is your vendor and manufacturer. That is where the advertising consideration is relevant. Those who advertise and whose name you recognize are probably a good place to start. I am sure that danek will concur with that assumption. I do not know him, but the answer that he gave you displays knowledge about the industry and his product and SERVICES. Make sure your vendor can give you the service and follow-up you need.

Good luck. I hope you find a good solution.