One of the problems with compressed air is the high cost of the power input that feeds the air compressors compared with the actual mechanical power that comes out at a compressed-air-powered device.
An example often used is the output of 1 horsepower using a vane-style air motor. A vane motor rated at 1 hp produces about 0.746 kW of rotational power from its shaft and translates this to a rotary motion that can drive a tool or a mixer. If typical specifications are consulted, we might find that this motor will consume 40 cfm at 100 psi to produce this level of power.
Now, if we look at a typical air-cooled lubricated rotary screw compressor running at 100 psi, we can find that it would consume a specific power of 18 kW for every 100 cfm of compressed air it produces. We can easily find this number from the Compressed Air & Gas Institute (CAGI) specifications published by most member manufacturers. Therefore, doing the math, we find that it takes about 18 × 40/100 = 7.2 kW of power input to the air compressor to produce about 0.746 output at the air motor shaft. Almost 10 times more power is required than is produced at the motor shaft. Most of the power is lost because of the heat of compression.
But it gets worse. The numbers presented assume a lossless compressed air system in which all of the air produced goes directly to the air motor without any leakage, pressure loss, or inefficiency resulting from partial loading of the compressor. In real life, these losses come into play to increase the actual cost of an air motor. Typically, about 30% of the compressed air produced at an air compressor is lost due to leakage before it gets to the motor. There’s also typically about 10 psi of system pressure loss that stems from air dryers, filters, and losses that occur from connectors and hoses, so the compressors must produce 110 psi to feed the motor 100 psi. This adds about 5% to the energy input.
KeyWords Tag：PONYAIR Industrial Air Compressors