Cost of Compressed Air
The process of compressing air can be wasteful. Of the total energy supplied to a compressor, as little as 8-10% is converted into usable energy at the point of use. This makes it a very expensive method of transferring energy.
Despite the high cost of production, many systems waste around 30% of compressed air through leaks, poor maintenance, misapplication and poor control.
Over a ten-year life of a compressor, the cost of energy to run the system far outweighs the capital investment. The graph below shows that maintenance accounts for 7% of total cost, yet this is a crucial activity for maximising the energy efficiency of any compressor.
Calculating your compressed air costs
Compressed air is an essential energy resource but it is commonly misused and wasted which incurs unnecessary cost and environmental impact. In order to make investment decisions to better manageyour compressed air utility or to improve the reliability of your system, you need to know the true costof compressed air. It is often quoted that compressed air is 10 times the cost of electricity but this isnot necessarily useful or accurate for the purposes of making investment decisions.
Another widely quoted estimation is:
Annual running cost = kW rating compressor x annual hours of operation x unit cost of electricity
However, this is merely the cost of running a compressor, not the whole system. To arrive at an exact figure will take some time and effort. As a guide, the more variables you include the more timeyou will spend and the more expensive compressed air will appear to be.
A ‘rule of thumb’
To save time, adapting average figures that are generally accepted in industry may be sufficient for your purposes. Those companies that have gone through the process of establishing their cost forcompressed air, normally end up with a figure:
between £ 0.01 and £0.03 per cubic metre (m3) of air
i.e. between 1p and 3p per m3
This is the total cost of producing a cubic metre of compressed air, i.e. it includes energy, capital, maintenance and management.
Variables affecting the cost of compressed air
There is this degree of variation in costs due to the wide range of factors affecting the cost of
compressed air, the factors include:
- unit cost of electricity
- working pressure
- leakage level
- air demand profile / operating hours
- type and age of compressors
- effectiveness of maintenance
- control systems
- level of air treatment
- distribution system sizing
- Some factors are easy to quantify (e.g. pressure and electricity cost), others such as the effectiveness of maintenance is less so.
Finally 1p or 3p?
So despite this variation of between 1p and 3p per cubic metre, it is still helpful to use these figures and choose one within the range depending on how efficient you think your current system is.
Compressed air is the best low cost saving opportunity of any site utility and therefore investments inits more effective use usually have a short payback period regardless of whether you use £0.01 or £0.03 per m3. If you have a pay-back period of less than 6 months at £ 0.01, then working out the exact cost is almost irrelevant.
Calculations taken from BCAS factsheet No.010 – The Cost of Compressed Air