Common energy efficiency measures for industrial compressed air systems are discussed below. Additionally, a number of measures that are applicable to refrigeration system compressors and motors are also applicable to compressed air systems.The most common areas for leaks are couplings, hoses, tubes, fittings, pressure regulators, open condensate traps and shut-off valves, pipe joints, disconnects, and thread sealants. The best way to detect leaks is to use an ultrasonic acoustic detector, which can recognize the high frequency hissing sounds associated with air leaks. Leak detection and repair programs should be ongoing efforts. In 1994, Mead-Johnson Nutritionals, a manufacturer of infant formula and adult nutritional supplements, implemented a compressed air system improvement project at its plant in Evansville, Indiana. Energy efficiency measures included the introduction of a monitoring system, the installation of new compressors, and the repair of leaks. The improved compressed air system of this plant functioned so efficiently that only two-thirds of the compressed air capacity had to be kept online. The company saved $102,000 per year in compressed air system energy costs with a payback period of just over 2.5 years. Additionally, the project helped the plant avoid the purchase of a new compressor . Turning off unnecessary compressed air. Equipment that is no longer using compressed air should have the air turned off completely. This can be done using a simple solenoid valve. Compressed air distribution systems should be checked when equipment has been reconfigured to ensure that no air is flowing to unused equipment or to obsolete parts of the compressed air distribution system. Modification of system in lieu of increased pressure.
For individual applications that require a higher pressure, instead of raising the operating pressure of the whole system, nft hydroponic system special equipment modifications should be considered, such as employing a booster, increasing a cylinder bore, changing gear ratios, or changing operation to off peak hours.Based on numerous industrial case studies, the average payback period for replacing compressed air with other applications is estimated at 11 months . Improved load management. Because of the large amount of energy consumed by compressors, whether in full operation or not, partial load operation should be avoided. For example, unloaded rotary screw compressors still consume 15% to 35% of full-load power while delivering no useful work . Air receivers can be employed near high demand areas to provide a supply buffer to meet short-term demand spikes that can exceed normal compressor capacity. In this way, the number of required online compressors may be reduced. Multi-stage compressors theoretically operate more efficiently than single-stage compressors. Multi-stage compressors save energy by cooling the air between stages, reducing the volume and work required to compress the air. Replacing single-stage compressors with two-stage compressors typically provides a payback period of two years or less . Using multiple smaller compressors instead of one large compressor can save energy as well. Large compressors consume more electricity when they are unloaded than do multiple smaller compressors with similar overall capacity. An analysis of U.S. case studies shows an average payback period for optimally sizing compressors of about 1.2 years . In June 2004, the Canandaigua Wine Company upgraded the compressed air system at its winery in Lodi, California. Before the project began, the winery was served by two 125 hp rotary screw compressors that operated at full load only during the 3-month fall grape crushing season.
During the rest of the year, however, the compressors were operated at part-load, which wasted energy. The company opted to install a 75 hp variable-speed compressor, which could be used to satisfy facility demand during the off-season while also providing supplemental power to the two 125 hp units during the fall crush season. Additionally, the company installed a new compressor control system, additional storage, and started a leak reduction campaign. The total energy savings attributable to the upgrade were estimated at 218,000 kWh per year, saving the company $27,000 annually . The simple payback period was estimated at 1.2 years. Similarly impressive savings were realized with a compressor upgrade at a Sara Lee bakery in Sacramento, California, in 2004. Prior to the upgrade, the company used one 100 hp and two 150 hp rotary screw compressors in its compressed air system. After the upgrade, the company used the 100 hp fixed-speed unit as its base compressor and a new 100 hp ASD compressor for variable loads. The project reduced annual facility energy consumption by 471,000 kWh and annual energy costs by around $40,000, while also saving the company$10,000 per year in avoided maintenance costs . The reported payback period was just 6.5 months. Pressure drop minimization. An excessive pressure drop will result in poor system performance and excessive energy consumption. Flow restrictions of any type in a system, such as an obstruction or roughness, results in higher operating pressures than is truly needed. Resistance to flow increases the drive energy on positive displacement compressors by 1% of connected power for each 2 psi of differential . The highest pressure drops are usually found at the points of use, including undersized or leaking hoses, tubes, disconnects, filters, regulators, valves, nozzles, and lubricators , as well as air/lubricant separators on lubricated rotary compressors and after-coolers, moisture separators, dryers, and filters .
Minimizing pressure drop requires a systems approach in design and maintenance. Air treatment components should be selected with the lowest possible pressure drop at specified maximum operating conditions and best performance. Manufacturers’ recommendations for maintenance should be followed, particularly in air filtering and drying equipment, which can have damaging moisture effects like pipe corrosion. Finally, the distance the air travels through the distribution system should be minimized. Audits of industrial facilities found that the payback period is typically shorter than 3 months for this measure . Inlet air temperature reduction. If airflow is kept constant, reducing the inlet air temperature reduces the energy used by the compressor. In many plants, it is possible to reduce the inlet air temperature to the compressor by taking suction from outside the building. As a rule of thumb, each temperature reduction of 5°F will save 1% compressor energy . A payback period of two to five years has been reported for importing fresh air . In addition to energy savings, compressor capacity is increased when cold air from outside is used. Industrial case studies have found an average payback period for importing outside air of less than 1.7 years , but costs can vary significantly depending on facility layout.Yasama Corporation U.S.A., a manufacturer of soy sauce, installed new compressor system controls at its Salem, Oregon, facility in 2004. Previously, the company ran its three compressors using inefficient individual load/unload controls. Additionally, the company added two 2,200 gallon air storage receivers to help handle the facility’s short-term peak loads. Under the new control strategy, the three compressors were sequenced to run most efficiently, leading to annual energy savings of 100,000 kWh and annual electricity savings of $5,100 . Additionally, the new control system allowed the company to better manage the total operating hours of each compressor as well as the number of starts per unit per hour, helping to reduce compressor wear and tear. In addition to energy savings, the application of controls can sometimes eliminate the need for some existing compressors, allowing extra compressors to be sold or kept for backup. Alternatively, hydroponic nft system capacity can be expanded without the purchase of additional compressors.Properly sized pipe diameters. Increasing pipe diameters to the greatest size that is feasible and economical for a compressed air system can help to minimize pressure losses and leaks, which reduces system operating pressures and leads to energy savings. Increasing pipe diameters typically reduces compressed air system energy consumption by 3% . Further savings can be realized by ensuring other system components are properly sized. H.B. Reese, a subsidiary of the Hershey Foods Company, overhauled the compressed air system piping network at its Hershey, Pennsylvania, facility in 1996. The plant modified and replaced undersized components such as filters, lubricators, fittings, and hoses, which lowered the minimum system operating pressure from 85 psi to 75 psi . Heat recovery. As much as 90% of the electrical energy used by an industrial air compressor is converted into heat. In many cases, a heat recovery unit can recover 50% to 90% of this available thermal energy and apply it to space heating, process heating, water heating, makeup air heating, boiler make-up water preheating, and heat pump applications .
It has been estimated that approximately 50,000 Btu/hour of recoverable heat is available for each 100 cfm of compressor capacity . Payback periods are typically less than one year . Heat recovery for space heating is not as common with water-cooled compressors because an extra stage of heat exchange is required and the temperature of the available heat is somewhat low. However, with large water-cooled compressors, recovery efficiencies of 50% to 60% are typical . Natural gas engine-driven air compressors. Gas engine-driven air compressors can replace electric compressors with some advantages and disadvantages. Gas engine-driven compressors are more expensive and can have higher maintenance costs, but may have lower overall operating costs depending on the relative costs of electricity and gas. Variable-speed capability is standard for gas-fired compressors, offering a high efficiency over a wide range of loads. Heat can be recovered from the engine jacket and exhaust system. However, gas engine-driven compressors have some drawbacks: they need more maintenance, have a shorter useful life, and sustain a greater likelihood of downtime. According to Galitsky et al. , gas engine-driven compressors currently account for less than 1% of the total air compressor market. Ultra Creative Corporation, a U.S. manufacturer of specialty plastic bags, installed gas engine-driven compressors in its plant in Brooklyn, New York. The initial costs were $85,000 each for two 220 hp units and $65,000 for one 95 hp unit. The company reported savings of $9,000 in monthly utilities .Energy-efficient system design. By sizing equipment properly and designing energy efficiency into a new facility, fruit and vegetable processors can minimize the energy consumption and operational costs of HVAC systems from the outset. This practice often saves money in the long run, as it is generally cheaper to install energy efficient HVAC equipment at building construction than it is to upgrade an existing building with an energy-efficient HVAC system later on, especially if those upgrades lead to production downtime. Recently, Mission Foods, a California manufacturer of specialty Mexican foods, worked with Southern California Edison to design its new production facility in Rancho Cucamonga to be as energy efficient as possible. The new facility had 50,000 square feet of office space, 125,000 square feet of manufacturing space, and 134,000 square feet of warehouse space. Mission Foods chose to install energy-efficient technologies for its HVAC systems and lighting systems, room occupancy sensors that turned off lights automatically, low-emissivity windows that reduced building heat gain, and skylights that provided natural lighting. The total project allowed the company to reduce the electricity consumption of its new facility by roughly 18% compared to its existing facilities, leading to annual energy savings of over $300,000 per year . Recommissioning. Before replacing HVAC system components to improve energy efficiency, the possibility of HVAC system recommissioning should be explored. Recommissioning is essentially the same process as commissioning, but applied to a building’s existing HVAC, controls, and electrical systems . Commissioning is the process of verifying that a new building functions as intended and communicating the intended performance to the building management team. This usually occurs when a new building is turned over for occupancy. In practice, commissioning costs are not included in design fees and often compete with other activities. As a result, commissioning is seldom pursued properly. It is critical that the building is commissioned to ensure that energy performance and operational goals are met.Recommissioning involves a detailed assessment of existing equipment performance and maintenance procedures for comparison to intended or design performance and maintenance procedures to identify and fix problem areas that might be hampering building energy efficiency. Recommissioning can be a cost-effective retrofit in itself, sometimes generating more savings than the cost of the retrofit measure. For example, recommissioning may help avoid the need to install new or additional equipment, leading to savings in capital investments.