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Compressed air is one of the largest energy users in industry and is used for a variety of purposes:

• Working energy air – for pneumatic tools and drills.
• Active air – to operate conveyor systems.
• Process air – for drying processes, injection blow moulding, packaging, or aeration.

 In some countries it accounts for up to 30% industrial electricity use.

Typical air compressor costs over a ten-year service life. Up to 73% of the cost is electricity use. Data source: Carbon Trust 2012.

Losses occur in all subsystems of compressed air system, as can be seen in this energy flow diagram of a typical compressed air system.

Measures that can potentially be taken to save energy include:

• Substituting to electrically driven systems – electrical drives have higher initial costs but lower operating costs.
• Regular and correct maintenance to reduce leaks and pressure losses.
• Correct compressor sizing. If higher pressure is only required for certain applications, secondary compressors for recompression should be used rather than basing the entire system on the highest pressure requirement.
• Recovering waste heat, using the heat recovered for other purposes such as pre-heating process water.
• Repairing compressed air leaks.

Potential energy-saving measures in compressed-air equipment.

In order to assess the energy saving potential, all subsystems need to be considered: application, distribution, processing and production.

Large-scale refrigeration, chillers and cool rooms are used in many industries, especially those dealing with meat and dairy products, food processing, and for process cooling in the chemical industry. The cost of running refrigeration far exceeds the cost of the equipment. In the food production and food retailing businesses, refrigeration can account for 50% of energy costs.

Energy efficiency measures include:

• Purchasing new compression refrigeration equipment; those with highest energy-saving specifications use around 30% less energy.
• Using sorption chillers, both ABsorption and ADsorption, which use a thermal compressor instead of a mechanical compressor. These can offer an efficient solution if a source of waste heat available and they can also be powered by solar thermal technology.
• Correct system sizing – refrigerators and chillers are often oversized.
• Adequate insulation and sealing of refrigerated rooms to keep heat out and minimise cooling requirements.
• Setting refrigerators at the highest permissible temperatures.
• Regular servicing and maintenance, including:
  • Cleaning condensers and evaporators.
  • Regular defrosting.
  • Detecting and repairing leaks.
  • Inspection and repair of pipe insulation.
• Using monitoring systems that check for changes in pressure and temperature.
• Recovering heat where possible to use to heat water or for process heat.
• Using passive cooling systems that can reduce or replace the energy demand for cooling.

A large range of technologies are currently available, especially for large-scale requirements, which can significantly reduce costs. These include cooling towers, hybrid coolers and free coolers. When planning new projects, their potential should be investigated and expert advice sought.

Overviews of cooling technologies currently available. Those driven by heat can be powered by solar thermal systems. However, many are only suitable for large-scale applications.

Electric drive systems convert electric energy into mechanical energy. They consist of an electric motor, a control system and a transmission system, such as a gearbox, which transfers the mechanical power of the electric motor to the working machine. Electric drives are used in pumps, cooling compressors, fans and compressors as well as material handling and processing equipment.

In the construction, industrial, transport and agriculture sectors, electric drives account for 53% of global final electricity consumption and over 70% of total industrial electricity consumption. It has been estimated that the implementation of energy efficiency improvements could reduce the worldwide electricity demand of electric motors by between 20% to 40% by 2040 compared to 2014.

Buying new machinery and replacing old machinery with more efficient machinery is a great opportunity to make economic savings.

Life cycle costs of electric drives at 3,000 annual operating hours over a service life of 7 years. Up to 95% of the costs are derived from the electricity used.

The greatest savings potential lies in optimising mechanical systems, followed by more efficient end-use devices, the installation of variable speed drives, adopting the use of electronic speed controls and the use of highly efficient motors.

Potential areas of saving regarding electric drives.

High energy savings can be achieved in the partial load range of electric drives, as illustrated in this example for an electrically driven pump.

Energy savings can also be made by optimising production processes, by removing energy-intensive steps and by improving operational control.

The payback periods for investments in energy efficiency measures related to electric drives are often only a few years.