Compressed air fail: Startling discovery

Here is a question from a past (and possibly future) client of a compressed air auditor.

Fig. 1: These very expensive lubricant free machines were installed to solve an air pressure problem due to overloading of the previous compressors. One or more of these may not have been needed.

Q: I managed to get a co-op student to help with compressed air leaks management/audit for the summer and we were also lucky to have had an opportunity to do the test you recommended a couple of years ago with full plant down.

Unfortunately, test results were quite disturbing in terms of how much flow we measured when every single machine and process was down — it turned out that one full air compressor is working just for leaks/non-process related air consumption.

Given this discovery I was wondering if you could weigh in on that and see if this could warrant a formal compressed air audit?

A: Congratulations on measuring your non-productive flow. Many plants never do this, so what you have done is out of ordinary. Considering that your compressors are 350 hp in size, produce 1,500 cfm, and consume 288 kW when fully loaded, the non-productive load is costing you an estimated 2.3 million kW hours of electricity consumption. This is worth about $230,000 per year in electricity costs.

Considering that detailed compressed air assessments usually find from 30% to 50% savings, I would suspect it would be very economical to have one conducted — especially since the power utility will support such a study with a funding grant.

You might also consider installing permanent flow meters and energy monitors on all your compressors, so you can evaluate your system efficiency and off hours load in the future without having to hire anyone or do any special study.

A side note: Even if you have a small system, it usually pays if you measure your system, as many surprises can await!