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  • Peg Minichiello

Effective Compressed Air Audit

What to Expect from an Effective Compressed Air Audit?

There has been a high increase in the general awareness of compressed air systems in the energy conservation field.  Popularly associated with several words such as the "the fourth utility, your most expensive utility, eight times more expensive than electricity, and a quarter-inch leak costs $9,000 in wasted energy.  This increasing awareness of compressed air systems has led to a relative increase in the numbers of compressed air auditors.  Due to this mass availability of auditors, plant operations, engineers and maintenance managers need to fully understand what they should expect from a complete air system review.

Begin with the Basics

Costs incurred on compressed air system reviews are mostly around the mid to high four figures or low five figures, but the paybacks on it are usually measured in months and not in years.  These reviews pave the way for the development of longer-term follow-up opportunities, thereby leading to a significant reduction in the operating cost.  Some plants have been able to slash their operating costs by a rate of 80 percent.

Most firms are of the opinion that the expenses generated on energy are variable, while in fact, a well-managed and well-controlled compressed air system can reduce the amount spent on production energy, which signifies a reduction in fixed costs.  This is mainly because as there is a decrease in the electrical power consumption, production rate increases or remains the same.

The net income effect experienced on a profit of $2,000,000 in sales at a net 5 percent margin, is similar to the impact a $100,000 energy reduction will have.  If done correctly, a 25 to 50 percent reduction in air demand and power costs can be experienced almost immediately from an active plant air system survey or audit.

The following are some of the frequently asked questions and issues about what drives the energy costs in compressed air systems which are discovered during a survey:

  • Is it leaks?

  • Running excessive pressure?

  • Lack of air-saving devices like venturi nozzles, air curtains, and the like?

  • Producing high-pressure air only to use it at low pressure?

  • Poor selection of primary air supply?

  • Poor selection or application of compressor controls?

  • Poor selection or application of filters, dryers, connectors, and regulators?

  • Poor air receiver placement?

  • Incorrect piping?

  • Poor selection of compressed air to do the job compared to an alternate energy source?

  • How can you compare relative costs if you don't know the price of compressed air?Alternatively, all of the above?

In most situations, the usual case is all of the above, including some other reasons.

A quality overview of the compressed air system should be provided by the survey, which should be in cost proportionality with the size of the system, system complexity, and its potential recovery.  Also, both short-term and long-term plans should be produced by the survey, to put in place, the essential control, and management of the air system.

There should be:

An adept concentration on what is required for the full cooperation of the interrelated parts of the system, and a need for the users to be able to fully comprehend the workings of these parts and the dynamics of their relationship.

  • A general guideline that can be followed to improve the system efficiency

  • Proper research into what specific programs and actions should be carried out, and their estimated costs and payback.

  • Development of a full sustainability program and if necessary, it should include essential plans for expansion.

Although useful, this minimum effort cannot produce the ultimate payback which can be gotten from more complete and detailed system analysis and training.

There should be additional follow-up programs, or even better, a more wholly controlled and fully managed compressed air systems after the first audit.

A minimum effort audit that is well planned can create a significant amount of savings and success needed to encourage the user in the future press for efficiency and returns to go for more in-depth programs.  Any audit that does not meet up to these expectations should not be accepted.

Assessing the System from the Supply Side

Evaluation should be made on the suitability of the existing air compressors as to the application and the general apparent performance and condition, without having to disassembly of the compressed air system or any mechanical work.

The evaluation report should adequately address the efficiency ratings, suitability of unloading controls, and capacity for translating lower air demand into lower power cost. 

Moreover, when necessary, obtain a report on the potential for modification, plus the capability for system sequencing, installation, and support systems, like the cooling water and ventilation, and information on a more superior or more power efficient equipment and controls variants.

Also, an evaluation of the compressed air treatment equipment which includes;

  • Installation, general apparent conditions, and performance;

  • the suitability for application;

  • the general effect on efficiency and energy costs, along with the impact on production and quality issues; should also be in the report.

Individually, data on the following should be carefully viewed:

  • In the case of the after-cooler, you should request for the effectiveness of the system; is it delivering a temperature of 100°F in the hottest ambient temperature.  If the system is not performing at this temperature, then check if it is possible to use auxiliary coolers at the dryer inlet.  There should also be a review of the installation geometry to the dryer.

  • Properly ensure the dryers and filters are appropriate in areas of size, efficiency, pressure drop, and have the right controls for the application.  Make findings into the available options for modifications which could improve system performance and efficiency.  Checks should be made on the use of the auto drains, and ensure the sizing and installation are capable of enduring extreme ambient temperature.

  • Suitability evaluation should be done on the supply-side piping that is between the compressor and the system storage vessel, including efficiency, and pressure drop evaluation.  Also, the placement of the air receiver should conform to standards for control, storing dry air, and its ability to function with appropriate storage to offset capacity control response lag.

The operating control band for the compressor capacity controls should include the primary dry air storage for the production area, to ensure that the authorities are operating concerning actual production and not about false signals from internal piping and other pressure spikes - this is of high importance.

A practical review or audit will evaluate all the compressed air generation, treatment and distribution of air to the production area.  Although it is not necessary to include the recommendation of new equipment, any operating energy efficient methods that are currently available, and/or generic alternates for future considerations should be provided by the audit.

Reference should be made to the impact on productivity and quality by any recommendations provided.  It should also be able to answer the question on the capability of the unloading controls of translating lower demand for airflow into lower electrical usage - this is of utmost importance. 

The skills of the unloading controls depend on the type of compressor, type of power, the condition of the equipment, the piping, and storage capacity.

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