An automotive factory produces high quality vehicles, requiring top- notch, blemish-free finish on their very expensive product. In their final assembly building is a touch up paint booth, where workers occasionally use fume hoods supplied with compressed breathing air.
To supply pure compressed air that is free from the carbon monoxide that might be drawn in by an air compressor running near an idling vehicle, the company has installed breathing air purifiers. Each purifier has a desiccant air dryer on the front end and a catalyst filter on the back end — which breaks down any carbon monoxide present in the air to protect the workers.
When purchased, the purifier was sized extra large in order to cover any future expansion. As a result a 400-cfm unit was installed with a dew point controller that was designed to save purge flow if the breathing air flow was light. Studies of the system showed that the fume hood flow only consumes about 2% of the rating of the purifier or about 8 cfm on average — and workers are active only during an eight hour daytime shift. The rest of the time, there was no flow because workers were not present in the building.
A compressed air auditor conducted a study of the facility and placed data logging instruments to measure pressure, power and flow. Immediately on review of the data, the auditor could see that something was dominating the flow profile and was cycling every 5 minutes: this turned out to be the breathing air purifier. Even though the unit was rated at 60 cfm purge flow, it was consuming 75 cfm. And what was worse, the dew point control had been turned off. This meant the purge flow continued uninterrupted even though very little breathing air was actually used.
The cost for this purge at 10 cents per kWh works to $12,800 per year. The auditor calculates that about $10k could be saved by simply turning the dew point control to purge economy setting, a very good return for little effort.
Furthermore, the leakage and non-productive flow of the plant is estimated by observation of the flow on the weekend at 100 cfm. Leak detection and repair of even 50% of these leaks could save the company an extra $9,100 per year.