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Metering the output of an air compressor provides a continuous health check. This enables preventive maintenance to ensure high efficiency and lower electricity bills.

The Free Air Delivery (FAD) of a compressor is the amount of atmospheric air sucked in by the compressor at inlet (suction side) of the compressor. The compressor’s FAD rating gives only the amount of air it will suck in, and not the air it delivers at actual conditions. Hence there is always a gap between a compressor’s rating and the process requirement.

The FAD is always specified at an ideal 0% RH (Relative Humidity). Practically, the suction air contains appreciable amount of water vapor. During compression and subsequent cooling, some of the water vapor gets condensed and is drained out from the inter / after cooler. Even at peak performance levels, a variation of RH from 0% (dry air) to 70% (common) leads to a gap of 4% between the FAD rating and actual delivery.

Thus, the compressor output should be monitored to

  • Identify the gap between FAD rating and actual delivery
  • Identify the loading pattern of the plant
  • Compute the efficiency of the compressor.

Metering gives a continuous health check of the compressor, there by indicating the need for preventive maintenance for optimal output. This is in view of the fact that the operating cost and maintenance cost of the air compressors is very high. By efficient compressor running, savings on the electricity costs are imminent.

E.g.: Consider a 1500 SCFM Compressor operating at 7 bar g. The compressor motor with a rating of 250 KW would require 1 KW to generate 6 SCFM. Taking the cost of electrical power as 5/- per KW, the cost of compressed air assuming 12 hrs of operation is close to 45 lakhs annually.