1. Parameter's Approach to Relative Humidity Control August 25, 2011 by Clay Hile

2. Main Concepts  Different methods of humidity control  Air flow requirements  PGC’s two-temperature method  Advantages and limitations

3. Steam Injection DI Water Source Water Boiler To Room or Chamber

4. Desiccant Dryer Dry applications (set points with below freezing dew points)

5. Two Pressure System  Precise calibration applications for small volumes  NIST method  Can generate low dew points

6. Classic Two- Temperature Control

7. Accurate Precise control Uniformity The need for uniformity in larger areas requires more air flow.

8. Control areas from 2 cu.ft. to 45,000 cu.ft.

9. Uniformity Requires elevated air flows Typical Application: Dew point is constant Humidity differences across a room or chamber are generally temperature driven

10. Constant Dew Point Temp. goes up, RH goes down Temp. goes down, RH goes up

11. Walk-in Plan View Return 73°F/50%RH Supply 300 CFM 10 x 12 x 10 Room (1200 cube)

12. Room with Load 73°F/50%RH Supply Return 3000 BTU Heat Source 82°F

13. Constant Dew Point (53.3°F) / 15 Air Changes per Hour 73°F/50%RH Supply Return 3000 BTU Heat Source 82°F/37% RH

14. Improving Uniformity  Reduce internal load  Location of load  Increase air flow

15. Increased Air Flow

16. Parameter’s Two-Temperature Control (PGC’s Method)

17. Dehumidification 53° DP

18. Humidification

19. RH Compensation

20. Two-Temperature Control  Control dew point by controlling water spray temperature  Control relative humidity by maintaining a tight air temperature control

21.  Accurate – Sensor Dependent  Precise Control – Two- temperature method  Uniformity – Higher air flow and good distribution

22. Ability of Two-Temperature Control

23. Calibration  PGC provides the control and uniformity  Chilled Mirror or other reference sensor provides accuracy.

24. Limitations to the Parameter “two temperature”  Range – dew point must be above freezing.  Ramp Rates – larger saturator water volumes stabilize control but increase the time to ramp dew points.  Requires a humidity sensor.  Is not a primary standard.

25. Conclusion Two temperature method is a proven method to maintain precise humidity control in larger areas.