Compressed air is one of the most widely used forms of energy throughout many industries, with approximately 70% of manufacturers using a compressed air system.
Compressed air can be one of the most expensive forms of energy for manufacturing plants, often using more energy than other equipment. One horsepower of compressed air requires eight horsepower of electricity. With many air compressors running at efficiencies as low as 10 percent, there’s often plenty of room for improvement. Fortunately, 50% of compressed air systems at small- to medium-sized industrial facilities have opportunities for low-cost energy conservation.
What influences air compressor energy efficiency? Such factors include type, model, size, motor power rating, system design, control mechanisms, uses and maintenance schedule. The chief reason for inefficient air compression is the loss of heat generated from the increased temperature of pressurized air and from friction caused by the system’s many moving parts.
When it comes to air compressor efficiency, it’s important to examine the entire system, which includes not only the air compressor itself but supply lines, air storage tanks, air dryers, receivers and after-coolers. By making the right adjustments to your compressed air system, you can save significant amounts of energy and money.
Improve your system’s efficiency with the following approaches:
Improve the Quality of the Air Intake
There are three components of the air compression system that influence performance:
- Temperature. The temperature of the intake air determines the density of the air. Cool air requires less energy to compress.
- Composition. Clean intake air ensures that compressed air can move more smoothly through the system. Dirty air contains contaminants that accumulate and cause wear and tear as well as reduced storage capacity.
- Humidity. Moisture can be harmful to an air compression system since it accumulates inside the system, causing components to rust. This may lead to wear and tear as well as leaks and reduced storage capacity. Dry air is less likely to damage your air compression system and tools performing work at the point of use.
Match the Air Compressor Controls
Air compressor controls match the compressor output with the demands of the compressor system, which may consist of a single compressor or multiple compressors. Such controls are essential for air compressor system efficiency as well as high performance.
Compressed air systems are designed to maintain a certain range of pressure and to deliver a volume of air that varies with end-user demands. The control system decreases compressor output when the pressure reaches a certain level. If pressure drops, on the other hand, compressor output is increased.
The most precise control systems can maintain low average pressure without falling below system requirements. Falling below system requirements may cause equipment to function improperly. This is why it’s so important to match system controls with storage capacity.
The following controls can help increase the efficiency of single compressors:
- Start/stop controls turn compressors on and off depending on pressure.
- Load and unload functions unload the compressor to discharge pressure.
- Modulating controls manage flow need, while multistep controls allow compressors to operate at partially loaded conditions.
- Dual-Control/Auto-Dual controls allow the selection of either start/stop or load/unload.
- Variable displacement can operate in two or more partially loaded conditions.
- Variable speed drives continuously adjust drive motor speed to meet variable demand requirements.
- Systems with multiple compressors use system master controls to coordinate all the functions necessary to optimize compressed air.
- System master controls can coordinate compressed air systems when complexity exceeds the capabilities of local and network controls. Such controls can monitor system components and also trend data to enhance maintenance functions.
- Pressure/flow controllers store higher pressure air, which can later be used to meet fluctuations in demand.
A well-designed system should use the following: demand control, storage, compressor controls, good signal locations and overall control strategy. The primary goal of such a system is to deliver compressed air at the lowest stable pressure while supporting fluctuation with stored higher pressure compressed air.
For multiple compressors, sequencing controls can meet demand by running compressors to meet system loads, while taking them offline when not needed. Network controls also help manage loads for the entire system.
Improve System Design
There are five ways to improve the design of your air compressor system.
- Straighten the path. Narrow delivery lines or sharp bends in those delivery lines can cause increased friction and pressure drops in the system, which means less pressure reaching the point of use. A better design without so many bends and loops should produce more pressure using the same energy.
- Save energy when needed. A storage tank, or receiver, can buffer short-term demand changes and reduce on/off cycling. A tank can also prevent system pressure from dropping below minimum pressure requirements when demand is at its highest. A drop in pressure may cause system pressure to increase, which can result in wasted air pressure. Tanks are sized depending on the power of the compressor. A 50 hp air compressor, for example, needs a 50 gallon air receiver tank.
- Cool the intake air. Since the energy needed to compress cool air is less than the energy needed to compress warmer air, you can reduce the energy required for compression by moving the compressor intake into a shaded area outside. A reduction of 20 degrees Fahrenheit, for example, can lower operating costs by almost 3.8%.
- Use several small compressors. Oversized air compressors can be very inefficient because they use more energy per unit while operating with a partial load. Such systems may benefit from the use of many smaller compressors with sequencing controls, permitting portions of the system to be shut down merely by turning off some of the compressors.
- Recover waste heat. Waste heat can be used for boiling water for space heating and heating water. A properly designed heat recovery unit can recover 50-90% of the electrical energy used in air compression.
- Locate near areas of high demand. By locating air receivers near sources of high demand, it’s easier to meet demand with reduced overall compressor capacity.
Consider Compressed Air Needs
- Examine the load profile. A properly designed compressed air system should consider the load profile. If there are wide variations in air demand, the system will need to work efficiently when it’s under part-load. Multiple compressors will provide more economical energy use when there are large fluctuations in demand.
- Minimize artificial demand. Artificial demand is the excess air volume required for unregulated use when using higher pressure than necessary for applications. If an application requires 50 psi and receives 90 psi, the system is producing unused air. Pressure regulators at the end use can minimize artificial demand.
- Determine the correct pressure needed. Required pressure levels must consider system losses from filters, piping, separators and dryers. Raising discharge pressure will increase the demand of unregulated usage such as leaks. In other words, pressure increases will generate increased inefficiency. For example, a 2-psi increase in header pressure will increase energy consumption by as much as 1 percent because of the consumption of unregulated air. To save energy, you should consider how to achieve high performance while reducing system pressure.
- Examine proper supply and demand. Verify that air compressors are not too large for end use. Consider all end use, quantifying the volume of air needed for each application. A general assessment of your entire compressed air system should help investigate the distribution system for problems and minimize inappropriate uses of air.
- Use block diagrams and pressure profiles. Block diagrams will help identify all components in an air compression system. A pressure profile reveals the pressure drops in the system, which should provide feedback for adjusting controls. To complete a pressure profile, you’ll need to take measurements of the inlet to compressor, the differential across air/lubricant separator and the interstage on multi-stage compressors. By data logging system pressures and air flow, you can determine system disruptions, intermittent loads, system changes and general conditions. Variations in pressure and air flow can be managed with system controls to minimize the impact on production.
- Use compressed air storage. Storage can control demand events during demand peaks by reducing the rate of decay and the amount of pressure drop. It can also protect critical operations from other events in the system by turning off a compressor if necessary.
Minimize Pressure Drop
Pressure drops occur as compressed air travels through the distribution system. Excessive pressure drops may cause poor performance and elevated energy consumption. Pressure drops upstream from the compressor signal result in lower operating pressure for the end-user. This requires higher pressures to meet the compressor control settings. Before adding capacity or increasing system pressure, be sure to reduce pressure drops in the system. Compressed air equipment should be operated at the lowest efficient operating pressure for best results.
The following are ways to reduce pressure drops:
- Maintain proper system design. The most common reason for excessive pressure drop is the use of inadequate pipe size between the distribution header and the production equipment. This can happen if you choose piping based on the expected average compressed air demand without considering the maximum rate of flow.
- Maintain air filtering and drying equipment to minimize moisture.
- Ensure filters are free of dirt that restricts air flow and causes pressure drops. Timely maintenance and replacement of filter elements is critical to reducing pressure drop.
- Choose separators, dryers, filters and aftercoolers with the lowest possible pressure drop. A typical pressure differential for a filter, hose and pressure regulator is 7 pounds per square inch differential (psid).
- Choose regulators, hoses, lubricators and connections offering the best performance at the lowest pressure differential.
- Reduce the distance air travels through the compressed air system.
Many tools can operate effectively with air supply of 80 pounds per square inch gauge (psig) or less. By reducing the air compressor discharge pressure, you can reduce leakage rates, improve capacity and save money. Reductions in operating pressure, however, may require modifications to pressure regulators, filters and storage size. Keep in mind that if system pressure falls below minimum requirements, equipment may no longer function properly.
Reducing pressure drops allows a system to operate more efficiently at lower pressures. For machinery that uses large amounts of compressed air, operating the equipment at lower pressure levels can provide significant energy savings. Components like larger air cylinders may be necessary to maintain proper functionality at lower pressure levels, but the energy savings should exceed the cost of additional equipment.
Maintain Your Compressor
Poorly maintained air compression systems can cause wasted energy and money. This makes it important to constantly check your systems for leaks, premature wear and tear and the accumulation of contaminants.
- Fix leaks. Wasted air is the leading cause of energy loss in air compression systems, wasting as much as 20 to 30% of a compressor’s output. Even small leaks can be very costly, leaking large amounts of air over time if left uncorrected. Keep in mind that the loss of air is proportional to the size of the leak and the amount of supply pressure in the system.
Leaks not only waste energy, but they also cause drops in system pressure that make air tools less efficient. This lack of pressure means that equipment will run longer to achieve the same results. Increased running time also means additional maintenance and even downtime.
Detecting and fixing leaks can reduce energy loss to less than 10 percent of compressor output. Leaks can be found anywhere in the compressed air system, but most leaks occur in pressure regulators, open condensate traps and shut-off valves, disconnects, pipe joints, thread sealants, couplings, hoses, tubes and fittings.
To estimate the leakage in your compressed air system, take measurements that will determine the time it takes for the compressor to load and unload. Air leaks will make the compressor cycle on and off because of pressure drops caused by leaks. Calculate the percentage of total leakage by using the following form: Leakage (%) = [(on-load time in minutes x 100) / (on-load time in minutes + off-load time in minutes)]. In a well-maintained system, the percentage should be less than 10%. A poorly-maintained system will reveal leakage of 20% or more.
- Leak detection. An ultrasonic acoustic detector offers the best chance of locating leaks by recognizing the hissing sounds. Ultrasonic detectors offer the benefit of speed, accuracy, ease of use, versatility and the ability to run tests while equipment is running.
If you don’t have an ultrasonic leak detector, you can apply soapy water with paint brushes to likely trouble spots.
- Leak repair. Once you locate a leak, repairing it may simply be a matter of tightening connections. However, it may also require replacing couplings, pipe sections, hoses, joints, traps, fittings and drains. Be sure to fit them with the proper thread sealant.
Until you can repair a leak, you can reduce leaks by lowering the pressure in the compressed air system. Stabilize the system header pressure at the lowest range to minimize leakage rate.
- Prevention. A proper leak prevention program can help identify and address future leaks. It will also help maintain an efficient, stable and cost effective air compression system. A leak prevention program can be beneficial by doing the following:
- Determine the cost of air leaks. This will serve as a baseline to determine the effectiveness of repairs.
- Identify leaks. Although an ultrasonic acoustic leak detector is most effective, a hand-held meter can also help identify leaks.
- Document the leaks. Document the size, location, type and estimated cost of a leak so you can track where and how leaks occur.
- Prioritize larger leaks.
- Adjust controls to maximize energy use.
- Document repairs. Such documentation can indicate the equipment that may be causing reoccurring problems.
- Periodic reviews. Periodic checks will help keep your system efficient.
- Change filters. Filters are used to ensure that clean air reaches end-users. Dust, dirt and grease can clog filters, causing a drop in system air pressure. If filters aren’t cleaned, pressure drops can require more energy to maintain the same pressure. Also, be sure to use low pressure drop, long-life filters and also size filters based on the maximum rate of flow.
- Maintenance. Be sure that procedures are in place for maintaining the compressed air system and that employees are properly trained in these procedures. This should keep the system running efficiently for years to come.
Fortunately, there are many approaches to improving the efficiency of your compressed air system. With proper maintenance, there’s no reason your system can’t provide cost savings along with high performance.
Quincy’s Efficient Air Compressors
Quincy can ensure high performance and minimal energy use with power-saving options on its line. Energy efficiency translates to cost savings for your business.
Variable Speed Compressors. The Quincy QGV®️ family of variable speed compressors offers energy-efficient design across the broadest operating range. Our Variable Speed Drives (VSDs) automatically regulate speed to ensure compressor output matches demand, offering 35% energy savings over conventional fixed-speed rotary screw compressors.
Variable Capacity Control. Quincy’s patented Power$ync™ technology offers a variable capacity control compressor that’s more efficient for operations requiring 50% to 100% flow. If the entire capacity of the compressor isn’t needed that often, Power$ync™ can easily reduce air flow output. Our Variable Capacity Control compressors offer 30% energy savings over conventional rotary screw compressors.