How to determine the cost of compressed air in industrial plants

Determining the cost of compressed air and understanding what drives its increase can help you minimise a few digits on your energy bills. As we all know, most industrial facilities need some form of compressed air, whether it's to run a simple air tool or for more complicated tasks such as tyre operation.

However, few industries set their eyes on compressed air systems and when they do they find that they are not running it as efficiently as possible, resulting in wasted energy and higher bills. In fact, most plants that use compressed air could probably do with a new set of eyes on their system.

For example, if you want to determine the cost of compressed air and improve the system, it is relevant to check the following:

• Local electricity tariffs.
• The length of the hose.
• The size of the machine.
• The air usage requirements of your tools.
• The different variables such as altitude, temperature and relative humidity of your working environment.

This directly affects energy efficiency and therefore the cost of compressed air, but if you can make at least one or two improvements to the system itself it will certainly reduce costs in the long run.

When it comes to industrial environments such as bottling plants and pharmaceutical facilities, compressed air systems tend to consume more energy and operate more efficiently. more than anything else. Compressed air is said to be one of the most expensive sources of energy and its typical efficiency can be as low as 10% -15%.

It makes sense, then, that the lifetime energy cost of the energy consumed is much more expensive than the initial cost of the compressor itself, so much so that the 80% of total cost of your compressed air system will be the electricity it consumes. For managers looking to reduce costs there is no better place to start than the compressed air system.

But, to achieve this, it is important to know how to calculate the efficiency of a compressed air system and determine the cost of compressed air in industrial plants, using the following formula:

Where:

• bhp: Engine power at full load (often higher than the engine nameplate). This power rating (horsepower) should be verified in the technical specifications of the equipment.
• 0.746: Conversion constant between hp and kW
• Percentage of time: Percentage of time running at the operational level. To do this, add the number of days per year your facility operates and multiply it by the number of hours the plant operates on an average working day.
• Percentage of full bhp load: You can look at your electricity bill and its utility will tell you what you are being charged per kilowatt-hour. 
• Engine efficiency: Efficiency of the engine at this level of operation. To obtain this number, you should refer to the section of the Compressed Air and Gas Institute (CAGI) performance data sheet and look in row 7 where you will find a number expressed as a percentage next to "Nominal efficiency of the drive motor".

Here is an example for determining the cost of compressed air in industrial plants using the formula described above.

Let's say you are trying to calculate the cost of a 200 hp compressor with a full load bhp of 215 hp, and you run it for 5,000 hours per year. If your electricity rate is $ 0.07 dollars / kwh and the efficiency of your motor is 95%, the cost would be as follows:

This formula assumes that the compressor is always operating at full load and to achieve a more realistic calculation, it is suggested to modify the equation to account for part load. How? By multiplying by the percentage of time the compressor spends at part load, as well as by the percentage of full load.

If you run the above compressor at 40% of full bhp for 50% of time with an efficiency of 90%, this is what the cost would look like:

Don't forget to consult the section of the performance data sheet The Compressed Air and Gas Institute (CAGI) to verify to obtain the actual number of the "Rated Efficiency of the Drive Motor".

Determining the cost of compressed air is the first step to increasing your energy efficiency, ROI and reducing your bills, and you need to know what it costs. 9 ways to optimise a compressed air systemThis will allow you to guide maintenance personnel through a reference route that will improve the quality of the system and your investment.

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