Control Demand to Contain Expenses

By R. Scot Foss, Plant Air Technology

Engineered responses to demand will bring compressed air savings.

Since compressed air is our least understood utility, it should be no surprise that most of the time we throw power at poorly defined problems.  Problem solving using brute force is extremely expensive from a capital and an operating cost point of view.

Phone calls from irate users provide the best information about problems.  Users demand what they think is lacking on the supply end.  A large part of this problem stems from inappropriate assignment of responsibility.

Users in 99% of the systems are not responsible for controlling how they use compressed air or how much they use.  Users have no requirement to apply reasonable engineering to any installation.  Often, a user has no idea how much air an application needs or even if the application is appropriate.  Please remember that it takes at least 7 horsepower of electricity to generate 1 horsepower of compressed air power.

Employees at the using point are allowed to adjust the regulators to a maximum pressure or not use one if they see fit.  Existing leaks can continue to grow at an unmanageable rate.  Any worker on the floor can apply an open-air line with five-figure consequences.  Production can install a piece of equipment with catastrophic consequences for other users.  Applications can be installed with critical pressure requirements that can’t work.  All this can be done without discussion between the user and the compressor room operators.

Sooner or later any one or all the above situations will motivate a representative of production to use the instrument of choice in the compressed air utility system.  This instrument of choice is of course, the telephone.  The magical word is spoken that expresses the standard for compressed air.  The standard is “more”.  But more what?

You see, production doesn’t specify whether it’s more power, more volume, or more pressure.  When there is an inappropriate assignment of responsibility, no database, and little understanding of compressed air, it’s easy to understand how such vague requests arise.

In a system I recently renovated, a similar call was taken by a powerhouse operator.  He checked his instrumentation and told the caller that the problem was in the demand end.  The operator stated that adding power would not help the situation.  The caller reported the operator for being insubordinate.

Before the system was reconfigured, the operator turned on all available power and hoped the calls would stop.  The net result of this response to unreasonable demand was inflated expenses.  Here, the peak electrical load ratcheted the distribution demand charge up for the next 11 months.

In this case, investigation of the problem proved that the operator was right.  The problem in demand was the result of high volume and short cycles.  This demand caused a pressure drop in the sector of the air system where the demand surge occurred.  The application was reconfigured to eliminate demand surges caused by high-volume, short-cycle usage.

The complete lack of information frustrates efforts to determine the condition of the system and problem definition.  Usually plant engineering and maintenance assume full responsibility for the workability of all equipment on the demand side of the system.

Often, production management incorrectly assumes that whatever occurs in the “black hole” of demand can be improved by changing supply.  One can purchase three times more power than is necessary in he name of responsibility without authority.

Without a working knowledge of the dynamics of demand or authority to venture into the users area, hopes for finding a solution evaporate.  We haplessly add more power or buy another prepackaged solution to another poorly defined problem.  Since this procedure has quieted the irate callers before, why should one doubt the effectiveness today?

Experience has been a good teacher, hasn’t it?  My first supervisor told me that experience was what you got when you didn’t get what you wanted.  For at least a number if times, power will cure the most ill of systems.

Unfortunately, aside from the obvious cost, as you add more and more power, you will get fewer and fewer results.  The day comes when the next compressor produces no noticeable results.  At this point there is no recourse but to abandon the confines of the compressor room.  WE must seek demand-side solutions, despite the lack of interest and the protests of the user.

Think of the last time you applied power to solve a system’s problem.  Suppose you had three compressors and you added a fourth.  Simple math says that you added 33% more capacity.  When you turned on the unit, did the pressure rise 33%?  Did it rise even 10%?  It probably did not.  Did you try to reduce demand or reengineer installations with high-pressure differentials?

Maybe you could use an air storage unit with metered recovery.  Storage and metered recovery can reduce the horsepower that supports demand surges.  The storage and metered recovery combination reduces the rate of flow and spreads the surge demand requirements over a longer period of time.

The speed of air transmission may be the problem.  A demand surge causes a pressure decay in an under-capacity system.  In this case, you can increase the transmission capacity instead of the differential pressure for improved service.

Increasing the pressure requires a substantial amount of power and increases leads and unregulated demand.  Careful engineering reduces the impact of demand surges without adding power.

What if your production department increases its operating rate?  This means that all the installed hose, filters, regulators, etc., will see higher flow.  The elevated flow rates result in higher differential pressure.  Increased differential pressure reduces specific pressure to the equipment.

Should you increase the flow capability to increase the specific pressure, or add power to increase the supply pressure for the same result?  In most systems that I audit and reconfigure, 20 to 40% of the total demand usage has no value to production.

One of the major constituents of waste is leaks.  Another wasteful constituent is excess air volume consumed at workstations.  Wide-open regulators indicate waste.  If another compressor is added to increase the system’s pressure, It will increase waste also.

Without standards for compressed air usage, it should not be surprising that these situations are commonplace.  As utility costs escalate, the effects of dealing with compressed air waste become a major concern.

R. Scot Foss is president of Plant Air Technology, Charlotte, N.C., a company specializing in system auditing and designing. This series of articles is based on his book, “Compressed Air System Solution Series”.  A portion of the proceeds from sales of the book is donated to children’s charities.  The book can be ordered through Southern Corporation.