Savings Ideas for Compressed Air
This month’s feature article will provide some food for thought on how to save money on your compressed-air operations. Of all your machinery, your air compressors are likely to be one of the most costly to operate. A 75 HP compressor running 24/5 at $.075 per KWH will consume about $25,000 in electricity annually. It takes eight horsepower of electricity to produce one horsepower of compressed air. So while compressed air is clean, readily available and simple to use, it can be very expensive.
Sequence Controls for multiple-compressor installations utilize a single master control that handles the duties of operating each compressor and coordinates the activities of all the compressors. The sum of the operating capacities (CFM) of the compressors in the system, determines the system peak capacity. Since most of the time the actual demand is far less than the peak capacity, an effective sequence controller will be required to maintain optimum efficiency. All of the compressors except the trim machine are to run at full capacity. The trim machine should be specified to handle the daily swings in demand. Other features of the sequencer include weekly operating schedule interlocks, air dryer sequencing, and reporting. Repairing System Leaks offers significant savings in compressed air operating expenses. The U.S. Department of Energy (DOE) estimates that 20% of the capacity of a poorly maintained system is used to fulfill the leaks in the system. The best way to determine the savings opportunity is to shut down your equipment but leave the air supply operating. Monitor how often your compressor will load over the course of an hour while only supplying the leaks. Start your repair program by frequently repairing any leaks that can be heard with the naked ear while the equipment is not running. If there are more opportunities after that, consider using an ultrasonic acoustic instrument. Point of Use Controls provides the capability to switch air supplies on and off dependent of the machine cycle. Many times air uses are quickly added without controls. It may be to assist the movement of parts on a chute or to blow debris from a point of operation. A simple valve wired to a PLC programmed output can significantly reduce air usage compared to the uncontrolled use. Also, consider an automatic main shut-off valve for each machine to eliminate any loss of air caused by leaks and uncontrolled points of use while the machine is idle (without depending on operator intervention). This could be as simple as a solenoid valve controlled by the MCR or the in-cycle bit and an off-delay time. See the chart for air flow rates based on tubing/leak size and system pressure. Then use the formula to calculate the cost savings by eliminating leaks and uncontrolled points. Compressor Heat Utilization allows the heat generated by the compressor to off-set winter time heating costs. In the example above, the 75 HP compressors is also a clean 187,000 BTU/hour heater. That is a substantial heater! Use a blower and some ducting to transfer the hot air to an area of the building that can benefit from the heat. This scheme should also incorporate some automatic controls that transfer the heat outside the building when not needed. The last thing you want is to save heating cost in the winter, but then lose them in the summer by overloading A/C units with the heat load from the compressors.