Question from a reader:

I was wanting to estimate my compressed air leakage level in my plant.  I watched my 100-hp compressor and saw that it was loaded for 87 seconds — and unloaded for 64 seconds on the weekend with no production.  How would I calculate leakage flow?

Answer from Ron Marshall:

You are in luck, it is very easy to estimate your non-production flow with a simple equation shown in this reference document:

https://www.compressedairchallenge.org/data/sites/1/media/library/factsheets/factsheet07.pdf

Using this equation, and your observations, we can estimate that your compressor is loaded at 87/(87+64) or 58%.  Most compressors running around 100 psi produce roughly 4 cfm per horsepower, so your low would be roughly 230 cfm (0.58 x 250 cfm).

By the way, you should take loaded and unloaded readings numerous times — perhaps 5 different cycles — to get a nice average. Sometimes compressor cycles can be variable due to random loads such as air dryers or drains.

We are calling this non-productive load because not all of it may be leakage … perhaps some is critical flow is being consumed by something in the plant, like HVAC systems or other controls, but it is a start.

In calculating the leakage cost, you might also calculate the 230 cfm times about 22 kW per 100 cfm = 51 kW power consumption.  If your plant runs full time 8,760 hours per year, this would consume about $44,300 in electricity costs at 10 cents per kWh.

Ouch! Time to look at reducing your non-productive load!