When you are purchasing a compressor, it can be difficult to decide which one to buy. You should be aware that about 80% of the lifetime cost for an average air compressor is due to electricity, the remainder is purchase price and maintenance. Often, a compressor will consume its total purchase price in electricity in a single year. Because electricity is such a big part of the total, you should be shopping for the one with the best efficiency.
But it is hard to figure out how much compressed air you will get for the electrical input, looking at the specifications is often confusing. Luckily, because of this difficulty, an organization called the Compressed Air and Gas Institute (CAGI) has developed a reporting standard.
CAGI has come up with a standard way of reporting important specifications of an air compressor, including something called the specific power, so people can compare between units. The specific power is one of the most important numbers reported, it is a measure of the power input for a given flow of air output and it is reported in kilowatts per 100 cfm. Think of it like a gas mileage rating for a car. But in this case, the lower the number the better.
When you are purchasing a compressor, you can ask for the CAGI Compressor Data Sheet for each compressor you are looking at and compare the specific power numbers. It should be noted that you should be comparing compressors of the same pressure rating, the higher the pressure rating the more power a compressor will consume per given unit of air output. This fact is a hint for you; lowering your pressure can save energy. You should also compare the Total Package Input Power at Zero Flow. If your compressor spends lots of time in the unloaded position, this will affect the total power consumption.
There are CAGI sheets for fixed speed rotary compressors and also special sheets for variable frequency style rotary compressors. While you are at it, you can also check out the CAGI sheets for the refrigerated air dryer you could be purchasing for your new air compressor!
If the compressor vendor selling the compressor does not have a CAGI sheet for the model they are selling, you should think twice. All major North American suppliers that are members of CAGI are required to publish their data on their websites. And to ensure the accuracy of the numbers they are reporting, there is a third party testing program to keep the manufacturers honest.
If you have had a compressed air assessment done at your plant, you will know the characteristics of your flow profile. Using this information, and the data taken from a CAGI data sheet, your compressed air auditor will likely be able to calculate the predicted operating cost of various types compressors and air dryers you choose to compare. This comparison can lead you to a good decision in terms of future energy costs. Good luck and happy hunting.