Is Dry, Dry Enough?
| A | Air Cooled Aftercooler - able to reduce air temp to ~80F and remove up to 50% of moisture. |
| B | Water Cooled Aftercooler - able to reduce temp to ~60F and remove up to 75% of moisture. |
| C | Refrigerating Dryer - able to reduce air temp to ~38F and remove up to 90% of moisture. |
| D | Desiccant Dryer - able to reduce air temp to ~-40F and remove 99% or more of moisture. |
| E | Remaining Moisture - ~1%. |
Remember to match your dryer purchase to your actual needs. Even if you have outside (exposed) lines requiring -40F dewpoint in winter, it can still be cost effective to purchase and operate a refrigerated dryer during warmer months when a 38F dewpoint will suffice.
After Cooling and Moisture Separation
For Every 20°F increase in atmospheric temperature, the ability to hold moisture just about doubles!
Dewpoint: the temperature at which the air becomes saturated with moisture and the moisture begins to condense.
Good aftercooling can extract 70-80% of the moisture in the air and dramatically reduce the moisture loading on the air dryers.
Gallons of Water Passing Through a 1000cfm Compressor Every 24 Hours at Operating Pressure of 100psig.
| Entering Air Temp |
Relative Humidity % |
||||
20 |
40 |
60 |
80 |
100 |
|
| 110°F | 128.98 |
257.99 |
386.97 |
515.98 |
644.97 |
| 100°F | 97.62 |
195.28 |
292.94 |
390.58 |
488.22 |
| 90°F | 73.06 |
146.13 |
219.19 |
292.25 |
360.37 |
| 80°F | 54.02 |
108.04 |
162.03 |
216.05 |
270.07 |
| 70°F | 39.42 |
78.84 |
118.26 |
155.21 |
194.64 |
| 60°F | 28.38 |
56.76 |
85.14 |
113.52 |
141.90 |
| 50°F | 20.13 |
40.26 |
60.41 |
80.55 |
100.68 |
| 40°F | 14.08 |
28.16 |
42.21 |
56.29 |
70.37 |
| 30°F | 9.56 |
19.12 |
28.68 |
38.24 |
47.79 |
| 20°F | 6.10 |
12.2 |
18.30 |
24.40 |
30.50 |
| 10°F | 3.83 |
7.66 |
11.56 |
15.34 |
19.02 |
| 0°F | 2.37 |
4.74 |
7.14 |
9.56 |
11.88 |
| -10°F | 1.41 |
2.79 |
4.20 |
5.61 |
7.01 |
| -20°F | .82 |
1.63 |
2.47 |
3.29 |
4.10 |
Dual Tower Desiccant Air Dryers
Contrary to the best intended opinions of those who feel the only way to dry and condition compressed air is by applying desiccant dryers on a 24 hr., 12 month per year basis ---the application of a refrigerating air dryer during the summer months can be a viable and more economical option.
- Apply existing desiccant dryer during winter when pneumatic valve freezing can be a problem.
- Switch over to the refrigerating dryer during summer where a pressure dew point of 36 to 39° F is acceptable.
- Savings will be gained in reduced desiccant dryer maintenance and reduced energy consumption.
Maintenance items on (heated) regenerative dryers include heating element failures, switching valve repair or replacement, blower failures, pre and after filter elements and above all the tower desiccant bead replacement every 2-3 years if the required winter dew point of -40° F is to be attained.
Heatless dryers can be costly to operate due to their high consumption of dry compressed air for wet tower purging---may be up to 15-17% of dry air volume.
Refrigerated Dryer Overview
- Simplicity and low operating costs.
- Easily serviced by qualified refrigeration technician or firm.
- Facilities with dual tower desiccant dryers that just need to keep dewpoint below ambient, can use refrigerated dryer most of the year and a PLC control can be used to monitor outside ambient temperature.
- Desiccant dryer would start when air dips below 45°F and refrigerant
dryer would start if air rises above 45°F.
Significant savings can be achieved from having the desiccant dryer down 6-8 months/year.
For additional information or assistance, contact Kelly Beiermann, Nebraska Public Power District.
Note: We encourage requests from Nebraska customers. Businesses outside of Nebraska will be directed to their utility for further information.
Source: Airometrix Mfg., Inc. 1999-2003
