What is compressed air?

Compressed air is a form of stored energy that is used to operate machinery, equipment, or industrial processes. Compressed air is used in most manufacturing and some service industries, especially in cases where the direct use of electricity to power tools or appliances is impractical or even dangerous.

A typical electrically driven air compressor compresses approximately 7 volumes of air at atmospheric pressure to 1 volume of higher pressure air (approximately 100 psig, or 7 bar). The high-pressure air thus obtained is distributed to the devices or tools in which it expands to atmospheric pressure, thereby releasing the energy necessary for their operation.

The heat recovered from the air compressor can be used as an energy efficiency measure in combination with other processes: for example, space heating and water heating.

Depending on the type of application, it may be necessary to control the excess humidity in the compressed air because of the possible problems experienced by the pipes (corrosion) and the equipment used.

Compressed air costs. This section will help you better understand what it costs to produce and use compressed air.

During the first ten years of a conventional air-cooled compressor (see Figure 2), running for two shifts, the operating cost (electricity and maintenance) will represent approximately 88% of the total cost of a lifetime. The initial cost of equipment and installation will represent the other 12%.

Since energy accounts for approximately 76% of the overall operating cost over the life of the product, it is essential to design and purchase the most efficient components for your compressed air system. It is recommended to make purchasing decisions taking into account the operating costs for the overall expected lifetime and NOT only according to the initial cost of the equipment.

Some industrial compressors are water-cooled. In these cases, additional costs related to water and its disposal, the costs of running the water cooling system, and the costs of pumping and chemical treatment should be assessed. Figure 4 is a simplified table that gives indications on the costs of electricity linked to operations on one, two or three shifts in a traditional industrial installation. The table shows these costs for air compressors with a power of 10, 15, 25, 50 and 100 HP. It is assumed that the average load of the compressors corresponds to 65% of the nominal load.

Note that this table uses a mixed electricity rate (energy and power demand) of $ 0.10 per kWh. Depending on your local rates, you will need to multiply the figures in Figure 4 by your local electricity rate (dollars per kWh) and then multiply the result by 10 to deduct your annual electricity costs. By contacting your local electric utility or compressed air service provider, they will help you determine your own blended electricity rate