Recovering Energy Cost in Compressed Air Systems
Written by Hank van Ormer
Wednesday, 09 June 2010 14:24
Page 1 of 5
RECOVERING ENERGY COST IN COMPRESSED AIR SYSTEMS
H.P (Hank) van Ormer President Air Power USA, Inc.
Air Power USA Inc. PO Box 292 Pickerington, OH 43147 (740) 862-4112 (Tel/Fax) www.airpowerusainc.com
RECOVERING ENERGY COST IN COMPRESSED AIR SYSTEMS – (It’s not always what you think it is!)
Opportunities for Compressed Air Energy Savings abound in everyone’s system Too often we focus on the air supply when the real bulk of the opportunities are on the demand side.
In the “Nirvana” of Compressed Air Systems, there is no wasted compressed air power – the air is supplied to the work being done at just the right pressure, quality and volume for effective production and the Compressed Air System always exactly meets demand. In the real world this NEVER happens. The Compressed Air System produces as much air as it can at the highest possible pressure and the production system used all it can – when – “there isn’t enough air the pressure falls and we add another compressor” – have you heard this scenario before? Sure you have! Compressed Air Energy Savings opportunities are the hot topic this year.
Still, much of the focus is on the supply side and how to produce and deliver the air to the system most efficiently. Items suck as to replace older, less efficient air compressors with newer more efficient ones – install more efficient and more responsive control systems to minimize part load efficiencies – replace older, less efficient motors with newer, higher efficiency motors, etc.
DO NOT misunderstand there are “real” Air Power Energy Savings on the supply side and a review of the supply side is very important.
Air Compressors: Basic design efficiency varies from 4 to 5.5 cfm per HP or 10 – 20% by type and 5 – 10% with same type.
Motor Efficiency: Older motors may very well have a ME of .85 to .90 where newer motors will be in the range of .93 to .96 this 4 –8% variance has about the same impact on the energy cost as the 5 – 105 variance within the same type of air compressor.
Unloading Controls: of the proper type and applied correctly will have a variance range of 5 – 1-% maximum. When the controls are grossly misapplied or of the improper type, this variance can escalate substantially.
NOTE: THE MOST IMPORTANT ASPECT OF UNLOADING CONTROLS IS THEY WILL BE CAPABLE AS APPLOED OF TRANSLATING LESS SYSTEM USAGE IN LOWER POWER COST – WITHOUT THIS THERE IS NO SIGNIFICANT POWER SAVINGS.
Air treatment in the form of Compressed Air Dryers and Filters will probably have less than a 5% variance when correctly applied with regard to performance and pressure loss. When misapplied these are items that can be and are often a very significant opportunity for Energy Savings.
As an adjunct to the supply side evaluation, you should establish a basic Energy Cost per CFM/PSIG for your compressor. This number is based on the Energy Rate – the basic compressor efficiency and the number of operating hours per year. This will allow easy calculation of potential Energy/Dollar recovery for identified system air savings opportunities. This may be a lot higher than you realize.
At .06 kWh – 8000 hours a year with an air supply that produces 4.0 cfm per input horsepower:
1 cfm cost - $100/Year in Power Cost
1 psig cost - $398/Year in Power Cost
(100 HP compressor in same condition)
Keep these numbers in mind as we identify basic opportunities in the Demand or Process Side of the Compressed Air System.
In summary – the supply side of the air system is very important – opportunities for savings exist upward from 10 –15% of the total bill even when reasonably well applied. More importantly, the supply side must be in tune with the total system in order to effectively translate less air usage into lower energy cost. However, most of the attention seems to be paid here and much less on the Demand or Production Process Side of the Air System which will probably account for 20 – 30% of the available opportunities.
Consider the real demand for air actually starts right at the process. How much air? At what quality? Is the required to allow the optimum production rate and quality? This is all there is, once we know that we can deliver “just the right air” to the process at the lowest possible cost. MUCH EASIER SAID THAN DONE!
Lets take a journey through your production compressed air system – other than the obvious leaks of which much has already been written – what are we looking for?
Pressure Loss in Piping – This area is often overlooked – we just assume it’s all right. Pressure loss measurement at full production load is all-important. In a well laid out system the interconnecting piping from the compressed air supply to the process and the header distribution piping – Should created NO pressure loss.
Let’s review some of the more common piping errors we find: