Compressed air is an important source of energy in industrial and commercial concerns. The most frequent areas of application are:

- cleaning, grinding, polishing, varnishing
- dusting, drying
- boring, screwing, hammering, casting
- regulation and control
- cooling
- tire service

With a modern facility, at most 20% of supplied energy is converted to mechanical energy. 80% is lost as waste heat. If compressed air must be further prepared (filtering, drying, lowering the pressure level) and the facility is badly maintained, then often less than 5% of supplied energy is transformed.

Leakages are a special problem with compressed air. In many companies facilities for compressed air are neglected. Therefore air (and thus money) escapes in many places. A 3 mm large hole causes annual losses of 1000 euro; a 6 mm large hole, 4500 euro (at 6 bar and 4000 hours per year).

Costs to produce 1 kWh of compressed air at 20 cent per kWh of electricity:

• 1.00 euro with an optimal facility, without additional equipment (5x as expensive as electricity)

• 4.00 euro with a poorly designed and maintained facility (20x as expensive as electricity)

Measures and improvements in using compressed air

• Cleaning, grinding, polishing: Replace pneumatics with electric drive.

• Painting: Replace pneumatic pistols with airless high-pressure systems that are also suitable for application of thick finishes; switch to powder finishes.

• Dusting, drying: analyze processes to see whether the expenditure is justified.

• Drilling, screwing: Switch to electrically driven devices.

• Hammers: Use electric hammers.

• Forges: Use forging hammer with air cushion for a flexible impact, but electric drive for the operation of the forge.

• Controls: Here there are often cheaper and at least technically equivalent electric or hydraulic solutions. Compressed air is important where it reacts flexibly to impacts and loads.

• Cooling: Cooling with compressed air is extremely uneconomical. Look for alternative systems.

• Tire service: Maintain all devices and use electrical screw driver instead of pneumatic ones.

General rules

Compressed air should be used only for special applications (furnace construction, explosion hazard areas). Provide compressed air only at the pressure that is actually needed. For special facilities (e.g., laboratory, semiconductor manufacture, low or very high pressure levels as for special finishes or in medicine and pharmacy), provide decentralized facilities with the necessary quality. Usually only small capacity is needed, and the cost of preparing compressed air with technical quality for laboratory purposes is very high.

The compressed air unit converts very large energy quantities in a classical company. The resulting waste heat can be recycled into hot water and air can be heated for finishing or heating a hall.

Immediate measures

• Check the tightness of the compressed air network while all connected components are stopped (hiss, pressure loss; check for leaks with ultrasonic measuring instruments). In some enterprises here there is a loss of over 50%.

• Check the load and idle running times of the compressor (indicator on the compressor, measurement of the power input; more than 50% idle running times means the compressor is too large).

• On sporadic loading of compressed air, use a buffer tank at the withdrawal point in order to avoid large cross sections of a line and/or extra large compressor capacity.

• Switch off compressed air when company is inactive (at night, weekends).

• Replace old pneumatic components (hoses, small hand tools, connections).

• Lead air supply lines in the walls inside a pipe (avoids hidden corrosion, easy to check).

• Adapt the pressure level to the requirements: Each bar of system pressure less saves 6 - 10% on energy.

Long-term measures and investments

• Create a compressed air plan with the following information: application, equipment (branch, type), necessary pressure, amount of air per hour.

• Localization of the different intended purposes in a plan with indication of the necessary amount of air.

• Record the existing air supply lines with indication of material and cross sections.

• Control cross sections by means of flow pressure measurement.
• Compute the necessary amounts of air and pressure.
• Determine the necessary air quality.
• Design the compressed air station (compressor, cooler, heat recovery).

• Divide the compressed air network into several zones (easier to find errors).

• Establish supply rings (smaller cross sections, high supply security).

• Net-compatible regulation of the compressor, no hard switching with reactions into electric system, use of frequency converters as output regulators.

• Separate measurement of current consumption for entire compressed air system.

• Time-dependent release for certain consumers (ventilation, etc.)

• On selection of a new compressor, power input with no-load operation should be as small as possible.

• Several small compressors are advantageous over a single larger one. The control between the compressors has to ensure that all devices exhibit an approximately same cyclic duration.

• Adjust compressor to application requirements: Savings of up to 20% of energy are possible if the aggregates are speed controlled or under superordinate controls that switch the compressors on or off depending upon load.

• Over 90% of the energy used in compressors is reusable as waste heat for heating purposes; oil coolers can contribute over a heat exchanger to the space heating!

Source: Austrian Chamber of Commerce