The Top 10 Parasites of Compressed Air Efficiency
how to maintain and improve performance in your compressed air systems
Of all the electricity used in the nation for manufacturing processes, an estimated 10 percent is consumed by compressed air systems. That's about $4.5 billion in expenditures, according to the U.S. Department of Energy (DOE). It is not uncommon for a large business to spend more than $1 million a year just to run air compressors. That is a considerable expense, and an area ripe with savings opportunities.
Compressed air is clean and easy to use. It is also inherently inefficient – about 10 percent efficient according to the DOE. With proper design, maintenance, and use you can optimize air systems to reduce electrical demand, limit impact on the environment, enhance performance, and increase profit.
Many compressed air systems were designed and installed many years ago when the cost of electricity wasn't a prime consideration. With electricity more expensive today – as much as 20 cents per kilowatt hour in some parts of the country – proper system design, use and maintenance can improve your operation and greatly and reduce your costs.
Many older compressed air installations are oversized. That is understandable as compressed air is as vital as electricity and designers often oversize the compressors to ensure that enough compressed air is available. However, the extra size adds no value – it only costs more money.
The most efficient design is a system that operates continually at full load. Any time an air compressor is operated at less than full load it operates less efficiently. Any time it is producing more than you need, you are wasting money.
Auditing your System: Since air is free, you pay only for the cost of compressing it. Your aim should be to balance the two sides of your compressed air systems – supply and demand – so that you pay to compress only to the needed pressure. The supply side is the equipment that, compresses, and distributes the air. The demand side is all the equipment using it.
An audit of your systems can be as simple as a walk-around by an experienced service person looking for obvious savings opportunities. A more extensive approach consists of measuring and monitoring your system to quantify supply and demand. Your local utility may help you finance such an audit.
TOP 10 PARASITES
Here are the leading causes of inefficiency in compressed air systems. While some may be obvious, it takes a trained professional to identify and solve many of the problems that are taking money away from your bottom line.
10. Improper Use
Any use of compressed air outside its intended purpose is wasteful. A common misuse is employees using an air hose to clean up or blow dust and debris from the workstation. In many cases, the hoses they use are high volume orifices that consume a lot of air. It can cost you thousands of dollars a year just to pay for employees cleaning themselves off with air hoses. These practices increase energy consumption needlessly. Here are some suggestions from the DOE to reduce the improper use of compressed air:
- Use air conditioning or fans to cool electrical cabinets instead of compressed air vortex tubes.
- Use blowers instead of compressed air to provide cooling, aspirating, agitating and mixing, or to inflate packaging.
- Use brushes, blowers, or vacuum systems instead of compressed air to clean parts or remove debris.
- Use blowers, electric actuators, or hydraulics instead of compressed air blasts to move parts.
9. Improper Application
Compressed air motors are sometimes the only alternative in a facility. But electric drive and hydraulic motors are more energy efficient, so it is wise to look carefully for opportunities to make a change, especially if your facility is older. When it is possible to switch motors, it is usually easy to do and inexpensive. The payback period is usually long, so such a move may make more sense as part of a larger compressed-air project.
The DOE also recommends use of pressure regulators. These will regulate the amount of compressed air used by each tool to match what the tool needs. Using pressure higher than needed increases system demand, uses more energy, and can increase equipment wear and tear.
8. Multiple-Compressor Schemes
As a facility grows, it's not uncommon to end up with a system that has several compressors. A single variable speed 100 hp compressor is much more efficient that four standard 25 hp units. Multiple compressors are also difficult to control, and you may end up with multiple units all running at less than full capacity because the system is out of balance and the compressors are fighting each other.
When it comes to compressors, fewer is better. The fewer you have, the better the system will operate and the less you will pay for maintenance and energy.
7. Compressor Room Environment
A compressor consumes ambient air that is filled with unwanted items like dirt, pollution, and moisture. As air is compressed, so are the contaminants and moisture. It ultimately ends up in your compressed air system and equipment, causing performance and maintenance issues.
By allowing water and other contaminants into your system you are risking pipe rust, pre-mature oil breakdown and performance issues. Always provide the cleanest environment for your compressor to operate in.
6. Lack of System Maintenance
You need a regular preventive maintenance schedule to keep compressed air systems working properly and to prevent unplanned outages. For the most part, such maintenance involves checking filters, fluid levels, lubrication, belts, and other regular service as recommended by the manufacturer. Remember, however, that a manufacturer's recommendations may be designed to protect equipment from failure. You may want to do maintenance more often to keep your system in its optimal condition.
5. Inadequate Piping and Storage
Compressed air passing through pipes and hoses causes friction that reduces air pressure. If your piping is too small, you are paying to compress the air to a certain psi, and then losing that pressure due to friction.
Storage provides a buffer to help keep supply and demand equal. If your system is operating at full capacity, a worker using an air hose to clean up the workplace may increase your demand so that it exceeds the supply.
A storage system temporarily increases your supply to keep the system in balance and prevent the system from shutting down from lack of pressure. The recommended storage capacity is 7.5 gallons of storage per cubic feet per minute (cfm) of system airflow (7,500 gallons for a 1,000 cfm system). In sizing a storage tank, consider the volume of the piping in the facility, which also provides storage capacity.
4. Improper Pressure Settings
The majority of facilities run their compressed air systems at the highest pressure possible, typically 125 psi. Most equipment only needs 90 to 100 psi. A typical 1/4 hp hand tool requires 2 hp worth of compressed air for standard operation.
Every 10 psi increase boosts energy consumption by 5 percent – a needless expenditure. There may be cases in which you do want some margin, but a 5 psi margin is adequate for a 100 psi system. A storage system may provide the necessary margin.
3. Inappropriate Contaminant Removal Systems
Even if you take normal steps to keep your compressor room clean, air leaving the compressor will contain water, particulates, and oil. Therefore, every system should have contaminant removal equipment appropriate to the application and environment in which it operates.
A refrigerated air dryer acts just like an air conditioner. Hot air holds more moisture, so the dryer lowers the temperature enough so that most of the water droplets condense (between 35 and
39 degrees F).
Another type of dryer is used in applications, such as semi-conductor manufacturing, that can't tolerate any moisture in condensed air. A desiccant dryer uses material such as silica gel to collect all the water molecules. This has the same effect as cooling the air to -100 degrees F. You do pay for that amount of drying because about 17 percent of the dry compressed air is used in the moisture removal process.
In addition to moisture removal, filters remove particulates and oil vapors in the air. Filtration should only be used to provide the level of cleanliness needed for your application because every filter will create a pressure drop in your system – as much as 5 to 7 psi per filter. Remember, air is free and you are paying to add pressure – an extra 5 psi increases your energy consumption by 2.5 percent.
2. Compressor and Control Selection
Compressors are sized based on the flow of compressed air at a certain pressure. Today's variable-speed compressors are much more energy efficient than constant-speed models because they adjust to the demand of the compressed air system.
A common 50 hp compressor, for instance, may put out 220 cfm at 125 psi. Let's say that your demand on that compressor is only 110 cfm at 125 psi. With a constant speed compressor, you are using 50% of the capacity of the compressor while you are still consuming 85% of your full load energy consumption.
A variable-speed compressor is also a good choice if you expect to need more compressed air in the future. For example, you might need a 100 hp unit to meet future demand. A variable speed unit will operate efficiently at 50 or 75 hp to match your current demand and adjust to meet future demand.
1. Piping Leaks
According to a study by the Compressed Air and Gas Institute (CAGI), an average compressed air system loses 30 percent of its air through piping leaks. Only the most obvious leaks reveal themselves through hissing or other indications. If you can hear a leak, it is probably costing you thousands of dollars a year. It's also the type of leak that you probably repair right away.
It is the small, insidious leaks that add up to rob your system – and you. Such leaks occur in joints and old piping and from slight damage from being bumped by equipment or through normal expansion and contraction. You need an ultrasonic leak detector – a highly sensitive microphone and headset – to find such small leaks. Repairing them, and preventing them, has an immediate payback for your business.
An audit of your compressed air system can save you significant amounts of money while improving the environment. It takes a trained professional to recognize all the opportunities and to make the calculations necessary to understand what is best for your specific plant or application. Many companies conduct such audits, from specialists in air audits to utilities, equipment manufacturers, and engineering firms.
An audit's recommendations could be simple such as reducing wasteful use of compressed air for cleaning. Or it could involve more extensive changes, such as new compressors and control units. You can make informed business decisions once you know the current state of your compressed air systems. Ask for an audit soon and chase those parasites from your system.
About the Author
Jason Hall has been in the industrial compressed air industry since 1999, working for the top three manufacturers of air compressors. Jason has experience in air audits as well as working with bid/spec projects and government projects. Jason joined Peterson Power in 2005 as a Project Manager, and now heads up Peterson Power's Compressed Air Systems.
Compressed Air Challenge(r) – A voluntary collaboration of stakeholders with one purpose; to help you enjoy the benefits of improved performance of your compressed air system. www.compressedairchallenge.org.
Compressed Air and Gas Institute (CAGI) – For more than 80 years, CAGI has been working to improve production, proper use, and increased distribution of equipment used in compressed air and gas systems. www.cagi.org.
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