Saving Energy with Compressed Air
Concrete Measures For Enormous Energy Saving Potential
- 100% of a compressor's electrical energy consumption is converted into heat. With fluid-cooled rotary screw compressors, up to 96% of that energy can be recovered and reused. Perhaps surprisingly, the usable energy in compressed air actually comes from the ambient surroundings: During the compression process and conversion of the electrical drive energy into heat, the compressor charges the air it draws in with energy potential corresponding to approximately 25% of the compressor's electrical power consumption. This energy is only usable however once the compressed air expands at its point of use and in so doing absorbs heat energy from the surrounding environment.
Saving Energy - Today's technology offers compressed air users myriad ways to significantly reduce energy consumption and CO2 emissions. It has long been recognized that energy consumption accounts for the lion's share of compressed air costs, and this was already a subject of considerable discussion within the compressed air sector around the time of the first oil crisis in the early 1970s. During that period, rotary screw compressors were starting their ascendance as the technology of choice for industrial compressed air production.
Spotting this trend early on, Kaeser Kompressoren not only added rotary screw compressors to its extensive product range, but went on to develop its proprietary energy saving "Sigma Profile" screw airend rotors. "More air, more savings..." was already the slogan even back then. However, the topic of energy efficiency only came back to the forefront at the end of the '90s with the signing of the Kyoto Protocol. At about the same time, the EU launched the "Save II" initiative. A study carried out within the framework of this initiative gave rise to the "Druckluft effizient" (Efficient Compressed Air) campaign, which was a collaborative project between the VDMA (German Engineering Federation), Fraunhofer ISI, the German Energy Agency (Dena) and businesses from the compressed air sector.
Over 30% Energy Saving Potential
The study determined that compressed air systems in Europe had an average energy saving potentialof nearly 33%. This finding was further consolidated by compressed air audits carried out as part of another measurement program; the audits revealed potential energy savings for the companies studied of between 18- 70%, depending on circumstance. So, in spite of some improvements, many companies' compressed air installations are more akin to those from the 1970s than to today's energy efficient systems.
Electrical Drives With Enhanced Performance
In the last few years, it has been possible to develop electric motors that operate at unprecedented levels of efficiency. In order to unify the various energy efficiency standards for asynchronous motors from around the world as a globalized standard, the International Electrotechnical Commission (IEC) created the IEC 60034-30 international norm.
It defines the efficiency classes IE1 to IE3, with IE3 being the highest class. In Europe, motors complying with this premium efficiency class will be obligatory for drives from 7.5 - 375 kW as from Jan.1 , 2015. Kaeser, however, already began installing IE3 motors in its new rotary screw compressors in 2010, and the rest of the product range will follow suit in a gradual roll out.
Energy Saving Compressors
Modern compressors are prime examples of highly developed mechatronic systems. Consequently, their efficiency is not only determined by optimum interplay between mechanical and thermodynamic components, but also between electrical and electronic components. Power transmission too plays a key role: Modern direct drive systems eliminate the transmission losses associated with gear or belt driven systems as the drive motor and compressor airend rotate at the exactly the same speed. The energy efficiency of the airend itself can also be increased further through optimization of the screw rotor profile and ancillary equipment for cooling, as well as through minimization of internal pressure losses.
Flexible Internal Compressor Control
A further important efficiency enhancing component is the compressor's internal controller. In the past, these systems often only had one control mode, yet modern industrial PC-based systems offer up to five pre-programmed options, thereby enabling compressor performance to be precisely matched to suit compressed air demand.
Kaeser's new Sigma Control 2 controller also offers added advantages: This advanced system provides greater flexibility through its numerous interfaces and innovative plug-in communication modules. Therefore, connection to energy-saving master control systems, computer networks and/or remote diagnostics and monitoring systems, such as Kaeser's Teleservice facility, couldn't be easier. The large display located on the control panel also simplifies on-site communication with the system, whilst the addition of an RFID reader ensures service continuity, increases security and significantly raises service quality.
High Service Quality
Moreover, these controllers provide an excellent basis for planned preventive maintenance resulting from continuous monitoring of compressor status and even the compressed air filters. This is essential for any comprehensive service concept that strives to ensure best possible dependability and availability, as well as optimized energy and maintenance costs. Needless to say, service should not be restricted solely to the compressors and other components, but should extend to cover the compressed air system as a whole.
Energy Efficient Compressed Air Drying
The impact of compressed air treatment on the energy efficiency of a compressed air system should also not be underestimated; this is especially true of drying. Significant strides have been made in recent years regarding the most efficient and widely used process (for pressure dew points to + 3 °C) of refrigeration drying. New refrigerants and advanced refrigeration dryers equipped with energy saving cycling control, and with the ability to adapt to actual compressed air demand, have led to significant energy savings.
There's now even a highly efficient combination process involving refrigeration and desiccant drying designed for applications requiring considerably dryer air (pressure dew points to -40°C). In some instances this method can completely replace the far more energy intensive process of desiccant drying and, in other cases, it's even possible to use recyclable heat from the compressor to regenerate the desiccant material.
Analysis of Actual Compressed Air Demand
Of course it's necessary to achieve best possible efficiency from the individual components within the compressed air installation, but this requirement is not in itself sufficient to ensure optimized efficiency of the system as a whole. The key to success lies in the optimized integration of these separate components into the system. This is where computer-aided demand analyses such as Kaeser's ADA (Air Demand Analysis) prove invaluable: With their help, it is possible to determine actual compressed air demand over time, establish the efficiency of a compressed air system and to identify how availability and performance may be improved. Special planning software such as Kaeser's Energy Saving System (KESS), for example, can subsequently simulate and compare various system options, as well as accurately calculate potential energy savings.
Optimized Compressed Air Management
There are also many areas for potential cost savings when it comes to compressed air system monitoring and control. Advanced master control and management systems, such as the "Sigma Air Manager" (SAM), provide users with the transparency and performance required to tap into these savings. Featuring state-of-the-art adaptive 3-D-Control technology (patent-pending), the latest SAM versions are now more effective than ever. What sets these next generation controllers apart from conventional systems is that they are able to take the three crucial "dimensions" that affect energy-efficient compressor control within a compressed air station into consideration, namely switching losses associated with compressor start-up and shutdown; additional energy consumption for pressure increases above the required pressure; and control losses resulting from idling and FC losses. In order to ensure optimum performance, the SAM constantly analyses the relationship between these factors, calculates the best possible result and controls the compressors accordingly. Moreover, the SAM delivers exceptional cost transparency and provides preventative maintenance coordination for the entire compressed air system.
Utilizing Recyclable Compressor Heat
Heat recovery provides another major source of potential energy savings: Up to 96% of the energy fed into a compressor can be recovered and reused for heating purposes. Therefore, companies that factor this energy into their supply concept can benefit from substantial additional cost savings and reduce their impact on the environment though reduced CO2 emissions. This recycled energy can be used, for example, to provide space heating, to create hot air curtains, to heat service and process water or to preheat combustion air - the possibilities are almost endless.
Minimization of leakages ...
The energy losses incurred as a result of leakages in the compressed air distribution pipe network can be equated, in biological terms, to severe blood loss: leakage rates of 10-25% are common. Over the course of a year such losses add up to appreciable additional energy consumption and, as a consequence, costs. With help from modern detection equipment however, leakages can be quickly located and rectified. This enables users to keep losses to an absolute minimum, although sadly they can never be completely eliminated.
...And Numerous Other Small Shortcomings
There are also other causes of energy losses and large pressure differences within the compressed air distribution network. These causes include contamination in the piping, inadequate pipe diameter and unfavorable pipe layout that adversely affects flow performance. These shortcomings should therefore also be corrected or avoided.