While you run around “putting out fires” in the plant or engineering department, handle employee demands and/or work through your everyday list of tasks – do me another favor  and gather the information necessary to determine the cost of your compressed air. After all you can’t begin to save it until you know how much it is costing you. All you need to know is this…
                         
                     (bhp) x (0.746) x (#of operating hours) x ($/kWh) x (% time) x ( % full load bhp)
Cost =          ———————————————————————————————————————————
                                                                                   Motor Efficiency

                         Where bhp — Compressor shaft horsepower (generally higher than motor nameplate Hp)
                                       Percent Time — percentage of time running at this operating level
                                       Percent full-load bhp — bhp as percentage of full load bhp at this operating level
                                       Motor Efficiency — motor efficiency at this operating level

Go ahead, I’ll wait for you (as I look at my watch).

Now, for certain, there are folks in the company who know some, or maybe all of this information. All you have to do is find them,  convince them you need the info, wait for them to get it to you, learn about bhp (brake horsepower), plug the information into the formula, remember how to work long formulas and come up with a number you may or may not be confident with. No problem.

Or, if you are a math whiz like me, looking at that kind of formula can be a bit overwhelming. And I like to keep things simple. So here is reasonable number to calculate the cost of your compressed air – You can use $0.25/1000 standard Cubic Feet of compressed air use. Again, 25 cents per One-Thousand standard Cubic Feet of compressed air.

This is a good benchmark number to use throughout the US. We are aware that all of us are paying a different value for our electricity, which is the largest cost associated with generating compressed air. And using $0.25/1000 SCF could be a little lower or a bit higher than the value you get once you have time to use the above formula but it is a solid benchmark and worthy of using so you may get started placing a value on an important resource. The simplified value also takes into account equipment and installation and maintenance.

Having a value of your compressed air is the place to start. Next you should begin to measure the consumption of your air throughout the plant. A digital flow meter is a product to place at each leg of your system or machines in your plant to find air consumption. It has an optional summing remote display which can show current usage, the previous 24 hour usage or  the total cumulative consumption. It  also helpful to determine how much air existing leaks are wasting. Then you will be on your way to optimizing your system and implementing a reasonable compressed air savings program.

Kirk Edwards
Application Engineer
kirkedwards@exair.com