Compressor strategies keep money from vanishing into thin air

Estimates indicate that poorly designed and maintained compressed air systems in the United States account for up to $3.2 billion in wasted energy costs annually. You need a plan to do better.

By Robert A. Baker, Atlas Copco Compressors LLC October 9, 2009

As a homeowner, imagine a rain barrel that eliminates your water bills, provides enough water for showers, kitchen use and lawn irrigation. Or consider the technology behind a hybrid automobile engine, which selects its energy output based on the required draw.
While rain barrels and hybrid cars may seem like distant analogies for engineers and facility managers, similar concepts are being used today to help make compressed air systems far more efficient than their predecessors from even a few years ago. And, while these two systems, energy recovery and efficiency, provide significant measurable returns, they both count on regular maintenance to remain effective.
Technology and an emphasis on sustainability have both helped lead the charge for increased efficiency in the way we live. The same holds true for compressed air, which is often referred to as the Fourth Utility, along with electricity, water and natural gas. While compressed air is an effective and essential component of a number of manufacturing processes in a variety of industries, it is also regarded as a notoriously inefficient system by nature.
In fact, estimates indicate that poorly designed and maintained compressed air systems in the United States account for up to $3.2 billion in wasted energy costs annually. In spite of these challenges, compressed air technology continues to advance in order to provide increased energy efficiency in all types of manufacturing environments.

Hot water recovery
Industries that use hot water or steam in their manufacturing facilities can significantly reduce energy bills by taking advantage of compressors with hot water recovery systems. In many cases, 80% to 90% of the energy used to make compressed air can be recovered in the form of hot water.
The process for recapturing energy in the form of hot water as a byproduct of the heat generated from the compressed air process is quite simple. When air compressors compress air, they convert input electrical energy into heat. The majority of this heat is generated at the compression elements, and then removed at the oil cooler, intercooler and aftercooler. An energy recovery system can be incorporated into the design, which circulates cooling water through all of these components, resulting in a heat transfer that yields hot water at up to 195°F. This hot water is then pumped to a storage tank where it is available for use in various processes, offsetting the energy otherwise required to operate conventional water heaters.
Hot water or steam that is normally generated by industrial boilers uses electricity or heating fuels like oil or natural gas. When using recovered hot water from an air compressor, either directly or as pre-heated boiler feed water, the consumption of fuel can be dramatically reduced or in some cases, eliminated completely.
Air compressors that typically recover 90% of operational energy as heat are common. Think about that – all of the energy needed to run an air compressor can be recovered and reused in the operation of peripheral applications throughout the manufacturing facility.
Most industries can make use of hot water for space heating, showers and other general applications. However, the industries that will benefit the most are those that have a continuous need for hot water and steam in their processes. These typical users include:
• Food and milk processing plants (scalding, cleaning, sterilization, and melting)
• Pulp and paper industry (in the digester and evaporators, in bleaching and pulping)
• Textile industry (dyeing, and stabilization of manmade fibers)
• Pharmaceutical industry (fermentation and sterilization)
• Refineries, chemical and petrochemical plants (steam distillation, enhanced recovery, stripping, and heat tracing)
• Power plants (electricity generation), clean rooms (humidification).
• The energy and associated costs that would otherwise result from generating hot water are partially absorbed as a result of the byproduct energy from the air compressor.

Air on demand
Variable speed drives are a familiar concept that, like the hybrid automobile, has helped increase energy efficiency. Quite simply, a VSD air compressor monitors the compressed air demand, which directly relates to the energy draw and adjusts its output to accommodate immediate needs. When an air compressor is running at 100% to accommodate an energy draw that represents only 50% of the compressor’s maximum output, then half of the energy to power that compressor is immediate waste.
By varying the rate of output through a VSD compressor, the energy output directly matches the energy demands. Compared to a fixed speed drive compressor that is sized for the same application, a VSD compressor consumes on average 35% less power.
If you have a fixed speed drive compressor in use at your facility, there’s a good chance you are a prime candidate for a VSD – more than 90% of all compressor applications are potential candidates for replacement with a variable speed drive compressor, and the return on investment is often realized within two years. Combine that with the greater efficiency that is realized when you replace the older compressor and the savings will continue to add up.

The advantages
A variable speed drive compressor, when applicable, provides significant advantages:
Superior technology: Variable speed drive technology provides energy efficiency superior to all other control technologies available today in air compressor applications.
Cost savings: Variable speed drive compressors consume less energy than fixed speed compressors sized for the same application, in most cases, up to 35% less.
Production performance: Variable speed drive compressors vary their output – continually and automatically – to precisely match the compressed air demand.
Environmental stewardship: Reducing the demand for power helps lower greenhouse gas emissions, gas emissions that contribute to global warming.
Smart investmen: Investing in variable speed drive technology pays for itself through significantly lower compressed air energy costs.

Identify, fix leaks
While technological advancements have helped make today’s compressed air systems more efficient, there are also a number of areas where facility managers can optimize their existing systems, save energy costs, increase productivity and reduce their carbon footprint.
The bottom line is an air compressor is only as efficient as the integrity of the infrastructure that supports it. For example, a
Also consider that systems older than five years typically leak about 25% of all the air that is pumped through them, the losses quickly multiple exponentially. Analyzing a system for existing air leaks and fixing those leaks can dramatically reduce energy bills while simultaneously increasing the system’s efficiency.
To help prevent air leaks, a system should also be regularly monitored to maintain the system’s integrity and sustain optimal efficiency.
Additionally, a clean, dry compressed air piping network provides quality air, helps eliminate corrosion issues, reduces the required maintenance of the system’s end use tools, and more importantly, it may prevent the possibility of product contamination.
Properly functioning compressed air dryers, filters and zero air-loss drains will help keep water and sludge – two components that can foster corrosion and increase the potential for leaks – out of a compressed air system.
Compressed air is an essential component of the manufacturing universe. By analyzing existing systems and identifying areas where technological advances can increase efficiencies, plant managers can dramatically increase their facility’s efficiency and significantly reduce their energy costs.

Robert A. Baker is senior marketing support specialist for Atlas Copco Compressors LLC. For a free copy of Atlas Copco’s 156-page Compressed Air Best Practices Guide, please send an e-mail to Put "Manual-Plant Engineering" in the subject line and provide your delivery address in the body of the e-mail, and Atlas Copco will send you a complimentary copy.