Plant compressed air is expensive to produce, and rising energy costs are driving industrial facilities to search for a method to estimate the energy savings potential in their plant compressed air system. Most compressed air users are not aware of and do not know how to properly estimate their current operating costs. This requires the expense of hiring a local auditor or compressed air consultant to come on-site and perform some type of assessment. There also exists no standardized report card or numerical rating method developed that represents the overall efficiency
level of the system that can be used for comparison between facilities or for tracking progress over time.
Years of in-the-field experience from auditing hundreds of compressed air systems over a wide cross-section of industries were drawn upon to identify the key principles driving the efficiency of a compressed air system. This led to developing the unbiased and technically sound questions targeting the supply and demand side of the air system along with an efficiency value assigned to each of the multiple-choice answers to these questions.
The Efficiency Quotient (EQ) rating worksheet is a two-page document. This worksheet determines the efficiency score for the air system, estimates the current operating cost, and estimates the energy savings potential with an attractive return on investment. It consists of four sections: the supply side EQ rating, energy calculation, demand side EQ rating, and the EQ summary. Separate scores are developed independently for the supply and demand EQ rating sections.
These two numbers are then averaged to determine the overall system EQ rating (efficiency) score. In the energy calculations section the total energy consumption is estimated. This calculation takes into account the quantity and sizes of the compressors and dryers, and the energy to cool the compressors is included in the estimated annual operating costs.
The EQ rating score is directly related to the savings potential in a compressed air system.
In Table 1 we can see how systems with a lower EQ rating are more expensive to operate and present a greater energy savings opportunity than those with a higher EQ rating.
We can also see that the EQ rating is a management tool for monitoring the efficiency of the air system over time. Air systems are very dynamic and change almost daily in most facilities, as new pieces of air-using equipment are added and production equipment is modified. Periodic evaluations of the EQ rating will serve as a way to see if there is continuous improvement taking place or if the system is losing efficiency by comparing the current EQ rating to previous evaluations.
Larger corporations can use the EQ rating method as a way to fairly evaluate the energy savings potential of all of their facilities. The plants can then be prioritized for further evaluation so that capital is spent on those facilities with the greatest opportunity for energy savings. This approach has the side benefit of documenting the compressed air equipment at each facility and an estimate of the current operating costs.
Below is a diagram of the supply and demand side of a compressed air system.
As illustrated in this diagram, the supply side consists of the equipment in the compressors room(s). The demand side refers to the piping and the various end users of the air. Efficiency rating scores are determined for each part of the system. Then the overall system EQ or efficiency rating is then determined by combining these numbers.
Page one of the EQ rating worksheet is shown below and consists of eight questions.
A numerical value is assigned to each multiple choice answer. After these are selected they are totaled and subtracted from 100 to determine the supply side EQ rating. A score of 100 represents the perfect air system which is not economically practical to implement. It does however give us a basis for comparison and a standard against which we can determine if the system is improving or becoming less efficient.
Before leaving the compressor room we complete the energy calculation section.
All of the compressors are listed and only those that typically operate are included in the calculation. Nominal values for the motor horsepower are used as some compressors are operating at full load which is typically 10-12 percent above the nominal motor horsepower rating while other compressors are trimming and using less than their nominal motor horsepower. Any dryers in the systems are also listed and the energy for cooling the compressors is also included. Both air-cooled and water-cooled compressors require additional energy to produce cooling of the air or the water.
We then move on to the demand side portion of the system. By walking around the facility we can look for and identify those applications and situations that are wasting compressed air.
The final section is the EQ Summary. Here we first calculate the overall EQ rating score by averaging the supply and demand side scores. We then use this score to look up the energy savings potential percentage from the table shown on the worksheet. By using the operating cost estimate calculated earlier with this savings percentage, we can then determine the estimated annual dollar amount of energy savings potential for the compressed air system.
Once the opportunity for energy savings has been estimated, the user can confirm the actual operating costs, determine the actual energy savings potential, and develop an action plan for implementation to capture the opportunity.
The EQ rating worksheet estimates the overall efficiency of the compressor system and is available for download at no cost to conduct your own walk-through. An EQ app is also available in the iTunes store. The app tool is a calculation “worksheet” that provides an estimate of overall operating costs, system efficiency level, and potential savings from having a complete EQ analysis performed.
By using the unbiased and technically sound EQ rating worksheet, any corporation can quickly and cost effectively estimate in-house the energy savings potential that exists in its compressed air system.
Jan Zuercher, P.E., is the director of air systems for Quincy Compressor, a designer and manufacturer of reciprocating and rotary screw air compressors ranging from one-third to 350 horsepower, vacuum pumps, and air treatment components. Its products are used in the mining, drilling, concrete production, and shipbuilding industries. Nearly 40 percent of its rotary compressor sales are custom orders with one-of-a-kind configurations. For more, visit www.quincycompressor.com.