Often, for extra reliability, a main and spare compressor exist in a compressor room. The spare may be an old unit that has recently been replaced, turned off, but waiting to be fired up if the new compressor shuts down or is taken out of service for maintenance. This spare compressor consumes no power if it is not running, so it costs very little in annual electrical cost.
But often times, what is forgotten is the associated air dryer — and if it is a standard non-cycling refrigerated type, it could be consuming power for absolutely no reason.
The air dryer in the photograph is one such offender, its compressor long since taken out of general service and replaced with a screw compressor. This non-cycling dryer remains energized, consuming about one kilowatt of power, 7 days a week, 365 days per year, costing about $875 annually.
To make matters worse, the dryer has an internal timer drain that operates regularly, wasting a flow of 10 cfm every 1 minutes for 5 seconds. Further to this, the associated filter of this dryer has a leaking drain, consuming about 2 cfm of wasted compressed air. The cost for these compressed air uses is about $580, making the total cost of this dryer, which is processing no air, about $1,500 per year. This large facility has about ten similar dryers operating under the same conditions, so the costs add up!
Sometimes, the story gets even worse if the facility has any spare fixed-cycle heatless desiccant dryers, running and consuming 15% of the dryer rating in purge flow, yet processing no real air when the associated compressor is shut down. Dryers like these can cause costs to skyrocket.
Here are some tips on saving wasted dryer energy:
- When turning a compressor off, make sure the associated air dryer is also off.
- If the spare compressor must start automatically on failure of the main, consider using electrical interlock to start up the compressor and dryer simultaneously.
- One solution would be to purchase cycling style refrigerated dryers; if available in the desired size, these dryers consume little power when there is no air flow through them.
- If desiccant dryers are required, purchase dew point controls to shut down the purge when not required.
- Ensure that any compressed air drains are turned down to minimum or replaced with float or timer drains.
- Always fix any leakage on equipment that is left pressurized for standby purposes.