How much energy your compressed air dryer consumes is a complicated matter that depends on multiple variables. So let’s just address some questions that you should answer to begin arriving at an answer. We’ll divide these questions by air dryer type, since each uses energy differently.
1. Refrigerated Air Dryer
a. Your dryer has a refrigerant compressor. This is largest source of electricity demand within the dryer, followed by the condenser fan motor (air cooled units). Determine power ratings of these motors to estimate the energy use.
b.If your dryer is a cycling design, the refrigerant compressor will cycle on and off depending on air flow through the dryer.Estimate your load factor and apply this to the energy calculation.
c. Your dryer creates differential pressure. The inlet air pressure is higher than the outlet air pressure. This is a form of energy loss. Most refrigerated air dryers cause a pressure loss of 1 to 3 PSI. A widely accepted rule: each 2 PSI of pressure loss increases the air compressors energy consumption by 1%.
2. Heatless Desiccant Air Dryer
a.Heatless (Pressure Swing) air dryers purge between 15 to 18% of their rated inlet capacity. A 200 CFM nominally rated heatless air dryer purges 30 to 36 CFM at 100 PSIG. What is your cost per CFM?Heatless dryers are often the most energy intensive air dryers operate.
b.Heatless dryers typically incur 4-6 PSI of differential pressure, including pre- and after- filters, at clean/dry conditions. See the comment above regarding the cost of pressure loss.
c.If you use a dew point demand switching controller to reduce purging, apply a correction factor to the purge rate. Be sure to verify that the dew point demand switching feature is actually working. These features depend on sensors that are often un-maintained and non-functioning.
3. Heated Desiccant Air Dryers
a. Heated purge dryers consume 7% of the rated capacity for desiccant regeneration; also determine the power rating of the dryer’s heater and assume that the heater is energized 75% of the time.
b. Blower purge dryers consume 3% of the dryer’s rated capacity for desiccant regeneration; also determine the power rating of both the dryer’s heater and blower.Assume these components are energized 75% of the time.
c. Assume a pressure differential of 4-6 PSI for both types of heated air dryer.
4. Deliquescent Air Dryers
a. These dryers consume no energy and incur less than 1% pressure differential (excluding filters).
b. They are not, however, without operating cost. Substitute energy cost for desiccant replacement costs.
5. Membrane Air Dryers
Membrane dryers consume no energy directly. They purge compressed air for sweeping moisture from the permeable membrane. This purge rate can vary from 10 to 40 percent, depending on the dryer. Check the literature for your model and calculate your cost of compressed air per CFM.
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