Although air is free, the cost to compress, treat, and distribute compressed air is significant. It takes approximately 8 horsepower worth of electrical energy to produce 1 horsepower worth of compressed air energy. Despite this inefficient conversion of energy, compressed air usage surpasses both electric and hydraulic power sources for industry, largely based upon the prominent benefits of using compressed air. The efficiency focus of compressed air becomes that of producing it as inexpensively as possible and not wasting it.
The most expensive component in the total cost of ownership of a compressed air system is the energy required to produce and deliver an uninterrupted supply of clean, dry compressed air at a stable pressure to every application in the system. Over the lifespan of a typical compressor, energy typically costs several times more than the purchase price of the compressor. This fact makes it a wise decision to purchase the most energy efficient equipment available and to operate it in a manner so it delivers its maximum efficiency. The bottom line is, maximizing energy efficiency saves money.
Many manufacturers overlooked compressed air costs for years when power was inexpensive, but as energy costs have increased significantly, it is imperative that facilities become educated about how important the total cost of ownership of their compressed air system is to saving money. For example: A manufacturer operates a 200 hp compressor, 24 hours a day, 365 days a year. When the manufacturer installed the compressor, energy cost was $0.03 per kWh. The annual electric cost to operate that compressor was $41,273. As the average electricity rate has risen to $0.10 per kWh, the electric cost to operate that same compressor under the same conditions is now $137,578. As energy costs have increased, they have garnered the attention of facility managers, who are charged with finding new solutions to reduce costs.
Since compressed air is a very expensive utility, wasting it is to be avoided. There are three main ways in which compressed air is wasted in a compressed air system: leaks, artificial demand, and inappropriate usage.
Leaks are the most obvious source of compressed air waste. Air under pressure flows to areas of lower pressure. Any opening to the atmosphere that is large enough to allow an air molecule to pass through it will become a leak. And the amount of air that flows through the opening increases as the pressure differential between the compressed air and the atmosphere increases. Aging, rusted piping with threaded fittings presents the perfect opportunity for leaks. Cheap, ill-fitting quick disconnect fittings are a major source of leaks. Plastic or rubber tubing that feeds air to a component frequently becomes cracked or split due to aging, vibration, or chemical attack and leaks – often silently. In fact, approximately 80 percent of air leaks are not audible, and they go unnoticed and unrepaired. A quarter-inch air leak at 100 psi will waste 104 cfm, and consume approximately 25 hp.
Using the above energy cost formula, that quarter-inch leak will waste more than $17,000 a year in a system where the leak flows continuously for 8,760 hours, the power cost is $0.10/kWh, and the compressor drive motor has a 94% efficiency rating.
Estimates indicate that poorly designed and maintained compressed air systems in the United States account for up to $3.2 billion in wasted utility payments every year. A conservative estimate is that the average leak rate in United States manufacturing facilities is as high as 30%. Compressed air leaks account for a significant amount of wasted electricity and provide the greatest opportunity for energy savings. A careful examination of the compressed air system in a facility will likely reveal numerous leaks. Since a majority of these leaks are not audible, it is critical that the facility utilizes the latest technology in leak detection to locate leaks so that they can be repaired. Ultra-sonic leak detection can be provided through your compressed air supplier or other companies that specialize in this field.
Artificial demand is another source of wasted compressed air and it is based on the fact that any air consuming device, leaks included, will consume more air as the pressure differential between the inlet and discharge of the device increases. The reverse is also true. For example, if a pneumatic cylinder requires 1 cubic foot of air @ 80 psig to complete its stroke, that same operation will consume 1.21 cubic feet of air when the system pressure is increased to 100 psig. Accordingly, artificial demand is the increased consumption of compressed air that is a result of operating at a higher pressure than is required to obtain the full function of the air operated device. By operating a compressed air system at the lowest pressure possible, the facility can keep the wasteful artificial demand to a minimum.
Inappropriate usage is just that, using expensive compressed air to perform work that is more efficiently performed by some other source of power. Using compressed air to continuously blow loose debris from underneath a piece of machinery is an example of an inappropriate usage of compressed air. That cleaning task can be performed with a broom, an electric leaf blower, a fan, or a positive displacement blowerb – all of which are significantly more economical than using compressed air. Inappropriate applications should be identified and replaced with alternate, more economical sources of power.
Compressed air is an expensive utility to produce and wasting it should be avoided at all times. The best way to begin a compressed air cost reduction project is have a trained, compressed air professional perform a system assessment on the entire compressed air system. This assessment will establish the true cost of compressed air for the facility, identify leak sources and inappropriate applications, and calculate the artificial demand of the system. Armed with this data the facility can implement a cost reduction project that addresses the three areas (leaks, artificial demand, and inappropriate usage) that impact system efficiency and total cost of operation.
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