Quincy M

How To Estimate Power Costs?

To estimate power costs, you will need to know the following:

  1. What is the cost per KWH?
  2. How many hours per year does the compressor run?
  3. At what capacity will the compressor run or how many hours will the compressor run at various load levels?
  4. What are the brake horsepower requirements of the compressor at the required load levels?
  5. What is the motor efficiency?

It is important to use actual CFM requirements to figure the load level of the compressor.  Do not base power cost calculations on comments like, “About half the time we run at full load and about half the time we run at 70% of full load.” Full load for one machine may not be the same as full load for another machine. Always determine the exact air requirement in order to provide the customer with a power cost calculation that approximates his situation.

Motor efficiencies vary from horsepower to horsepower and from manufacturer to manufacturer within horsepower ranges. The only way to accurately figure power costs will be to use the motor efficiency number on the nameplate of the actual motor being used.

With the above information in hand, annual power costs can be estimated by using the following formulas:

  • kW=BHP x .746/motor efficiency

Example – Find the kW of a 100 HP, normal efficiency motor running at a 95 HP load.

  • kW = 95 x .746/.93 = 76.2
  • Cost per hour = KWH x power cost

Example – Find the cost per hour to operate the compressor in the above example assuming a cost per KWH of 7 cents.

  • Cost per hour = 76.2 x 0.07 = $5.334

To find the annual power costs, calculate the cost per hour of operating at the various anticipated load levels and multiply by the anticipated number of hours that the machine will operate at those load levels.

Compressed Air Myths

Myth:
Compressed air is not desirable source of power

Fact:
When properly applied, compressed air can be the best choice. It is a safe, clean source of power that is easy to use and maintain

Myth:
Compressed air is very expensive

Fact:
Like the other power sources (electric, battery and hydraulic), compressed air can be costly. Compressed air cost can be minimized through correct application, installation and maintenance.

Myth:
Compressed air is dirty

Fact:
This is generally not true. Poor system design or lack of basic maintenance can result in contaminated air at point of use

Myth:
More pressure is better

Fact:
Raising pressure system-wide will require more power on-line. Pressure problems are best solved at the point of use where they exist, not with more power in the compressor room

Myth:
Reducing compressor operating pressure will save energy

Fact:
How far pressure is reduced will determine the savings, the further it is reduced the less stable and reliable the system will become. The first time production is interrupted operating pressure will be returned to previous levels and savings will disappear

Myth:
Routine servicing is not required

Fact:
The longer you leave between compressor service intervals, the more likely it is that your compressor will break down. How long can you business run without compressed air? A dirty oil removal filter can increase your energy use by 2 percent and a clogged air/oil separator up to 5 percent

Common Leak Problem Areas

Air leaks are a significant source of wasted energy in a compressed air system, often wasting as much as 20-30% of the compressor’s output. Compressed air leaks can also contribute to problems with system operations, including:

  • Fluctuating system pressure, which can cause air tools and other air-operated equipment to function less efficiently, possibly affecting production
  • Excess compressor capacity, resulting in higher than necessary costs
  • Decreased service life and increased maintenance of supply equipment due to unnecessary cycling and increased run time

Proactive leak detection and repair can reduce leaks to less than 10% of compressor output. The most common leak problem areas are:

  • Couplings, hoses, tubes and fittings
  • Disconnects
  • Filters, regulators and lubricators
  • Open condensate traps
  • Pipe joints
  • Control and shut-off valves
  • Point of use devices
  • Flanges
  • Cylinder rod packing
  • Thread sealants

Once leaks have been repaired, the compressor control system should be re-evaluated to realize the total savings potential.  Quincy’s patented, Frost and Sullivan award-winning EQ process evaluates the overall efficiency of your compressed air system based on “Best Practices” solutions. Please visit www.quincycompressor.com for more information on our patented EQ process.

References: Improving Compressed Air System Performance: A Sourcebook for the Industry, Motor Challenge and Compressed Air Challenge, April 1998.

Meet Quincy Compressor

Quincy Compressor is a leading designer and manufacturer of reciprocating and rotary screw air compressors ranging from one-third to 350 horsepower; vacuum pumps and a full line of air treatment components.

In 1920, Quincy established its reputation for engineered solutions and provides uncompromising reliability for demanding applications. Its flagship products, QR-25 and QSI have proven to be reliable choices for users in some of the toughest conditions like mining, drilling, concrete production and shipbuilding.