Kaeser Compressors
Energy Savings in Compressed Air Systems
Evaluating Compressor Efficiency
Cost-justifying More Efficient Compressors
Waste Heat Recovery and the Importance of Maintenance 
Achieve Significant Savings Through Improved Energy Management
Evaluating Compressor Efficiency
Evaluate your compressed air costs and potential savings.
Compressed air is your most expensive utility.
     This is a fact that has been documented time and time again. It takes 7 to 8 hp of electricity to produce 1 hp worth of air force. Yet, this high energy cost quite often is overlooked. Here are some questions you should ask yourself.
  • Do you know your compressed air costs?
  • Do you know how much compressed air is really required for your plant?
  • Do you select compressed air equipment with energy costs in mind?
  • Do you monitor the use of compressed air like your other utilities?
     It is the purpose of this reference material to give you the information you need to answer these questions, save energy and improve your compressed air system operation.
Why evaluate energy costs?
     Depending on plant location and local power costs, the annual cost of electrical power can be equal to-or as much as two times greater than-the initial cost of the air compressor. Over a 10 year operating period, a 100 hp compressed air system that you bought for $40,000 will accumulate up to $800,000 in electrical power costs. Following a few simple steps can significantly reduce energy costs by as much as 35%.
Chart 1
Identifying the electrical cost of compressed air.
     To judge the magnitude of the opportunities that exist to save electrical power costs in your compressed air system, it is important to identify the electrical cost of compressed air. Chart 1 shows the relationship between compressor hp and energy cost. In addition, consider the following:
  • Direct cost of pressure: 
         Every 10 psig increase of pressure in a plant system requires about 5% more power to produce. For example:
         A 520 cfm compressor, delivering air at 110 psig, requires about 100 hp. However, at 100 psig, only 95 hp is required. Potential power cost savings (at 10 cents per kWh; 8,760* hrs.) is $3,750/year.
  • Indirect cost of pressure:
         System pressure affects air consumption on the use or demand side. The air system will automatically use more air at higher pressures. If there is no resulting increase in productivity, air is wasted. Increased air consumption caused by higher than needed pressure is called artificial demand.
         A system using 520 cfm at 110 psig inlet pressure will consume only 400 cfm at 80 psig. The potential power cost savings (520 efin - 400 cfm = 120 cfm = 24 hp, at 10 cents/ kWh; 8,760* hrs.) is $18,000/year.
         Also remember that the leakage rate is significantly reduced at lower pressures, further reducing power costs.
    * 8,760 hours is based on operating 24 hours/day, 7 days/week, 52 weeks/year.
  • The cost of wasted air volume.
         Each cfm of air volume wasted can be translated into extra compressor hp and is an identifiable cost. As shown by Chart 1, if this waste is recovered, the result will be $750/hp per year in lower energy costs.
  • Select the most efficient demand side.
         The magnitude of the above is solely dependent on the ability of the compressor control to translate reduced air flow into lower electrical power consumption.
Chart 2
         Chart 2 shows the relationship between the full load power required for a compressor at various air demands and common control types. It becomes apparent that the on line-off line control (dual control) is superior to other controls in translating savings in air consumption into real power savings. Looking at our example of reducing air consumption from 520 cfm to 400 cfm (77%), the compressor operating on dual control requires 83% of full load power. That is 12% less energy than when operated on modulation control. If the air consumption drops to 50%, the difference (dual vs. modulation) in energy consumption is increased even further, to 24%.
Cost-justifying More Efficient Compressors / Waste Heat Recovery and the Importance of Maintenance