The size and type of air dryer and filters used on your compressed air system can affect both energy efficiency and the quality of the air produced. Oversizing components can help improve these characteristics.
Often, when an air dryer is purchased, it is sized to exactly match the output capacity of the air compressor. If the air compressor produces 250 cfm of output, a 250 cfm rated air dryer is installed. But depending on the installation environment and the characteristics of the air dryer, this could be problematic.
Most air dryers sold in North America (ratings differ in other parts of the world) are rated using the “three 100 rule.” That is, for example, a refrigerated dryer would be rated at 100 psi, 100° F inlet air temperature, and 100° F ambient. If the conditions in your compressor room differ (and they very often do), say on a hot humid summer day, or always, if you have ventilation problems in your compressor room, then your air dryer will not be able to remove the necessary water vapor to achieve its rated output. If the inlet pressure is lower than 100 psi, and/or inlet and ambient temperatures higher, then to get rated dew point you must oversize the dryer. This basically means the dryer needs to have a higher rating than the connected compressor capacity. Sizing charts for derating dryers are offered for your information on most dryer manufacturer’s sales literature.
Oversizing the dryer has additional benefit, since the pressure drop across a compressed air component varies to the square of the flow change, having a larger dryer and associated compressed air filter will substantially reduce the pressure differential across both components. Every 2 psi reduction in pressure at the compressor discharge will reduce the full load power input to the air compressor, saving power. And if the chosen dryer, in the case of a refrigerated style, is a cycling dryer, one that turns its power consumption down with the change in moisture load, the extra dryer capacity will not cost any more in power consumption.
Some more related tips to save energy:
- Air dryers sold by manufacturers in North America may have Compressed Air and Gas Institute data sheets which show the compressor power consumption, power turn down with flow, and pressure drop across the dryer, use these sheets to help you choose the most appropriate air dryer.
- Air dryer pressure drop varies between manufacturer’s and sizes, always consult the dryer specifications when purchasing a new dryer and aim to choose one with the lowest pressure drop. Sometimes this means purchasing the next size higher.
- If you have a spare dryer, often higher capacity and reduced pressure drop can be gained by paralleling the dryers. Best results from this strategy are achieved if the dryers are cycling style.
- Carefully consider the type of dryer and main air filter your plant actually needs. Over drying or filtering causes higher compressed air losses and higher than needed pressure differential, leading to higher than desired compressor power consumption.
- There are mist eliminator style main filters available that have greatly reduced pressure differential and long life. These should be considered for general filtering.
- With any dryer you should consider installing airless condensate drains on the dryer and filters to reduce compressed air loss.
- Don’t forget the storage receivers, oversizing these have additional benefits too.
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