When you are looking to buy a compressor, remember that numbers matter. Most people just look at the sticker price when comparing brands of compressors, and often choose the lowest cost.
They will also look at the compressed air flow output rating and tend to like the models with the highest output per nominal horsepower. Given the choice between 100-hp compressors that produce, for example, 360 cfm, 400 cfm or 420 cfm of compressed air, many would choose the unit with the highest number.
But, looking at the pie chart in the graphic, which shows the proportions of the life cycle costs of a compressor running full time, 8,760 hours per year, it looks like the numbers related to the energy cost matter the most. In this case, the purchase price makes up only 4% of the compressor 10 year life cycle cost.
The energy cost for a given compressor is not always quoted by compressor salesmen, they are likely unaware of now many hours it will run, and sometimes they would rather you would not know the costs — but it is best if you ask about the energy performance numbers.
Fortunately, in North America most major compressor manufacturers belong to the Compressed Air & Gas Institute (CAGI) performance verification program and publish energy data on their air compressors. You can use these to compare annual costs based on known compressor duty.
For example, if a 100-hp compressor producing 400 cfm has a rated specific power of 21 kW per 100 cfm, it will consume 84 kW average while running full load. If running 8,000 hours per year, this would cost about $67,200 per year in energy costs at 10 cents per kWh energy cost.
If another compressor produces 400 cfm at a rated 22.5 kW per 100 cfm it will consume 90 kW of power and cost $72,000 per year. Over 10 years this difference in annual cost between the two units adds up to $48,000 in electricity costs, which is significant considering the purchase price of the two compressors is within $5,000 of each other.
The operating costs of each compressor might be quite different if the compressors operate part loaded; these costs depend on the part-load control mode of the compressors. Have your compressor vendor help you compare these costs.
When choosing a new compressor, make the decision on the right numbers — it could save you money in the long run!
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