Controlling Relative Humidity and Condensation in a CO2 Incubator
- 1. Controlling Relative Humidity and Condensation in a CO2 Incubator
- 2. Introduction Deborah Thibodeaux Science Director For more than 60 years, Baker has helped advance science, discovery and clinical care by pioneering innovative solutions for air containment and controlled environments. Our solutions include: • Biological safety cabinets • Clean benches • Fume hoods • CO2 Incubators • Controlled-oxygen workstations • Anaerobic chambers • Media conditioning systems Cheri Gaudet Marketing Specialist
- 3. Manufacturer Claim “Our CO2 incubator provides you with the optimal conditions for culture growth!” As scientists, it is our duty to investigate the truth of such claims.
- 4. Define “Optimal” • 37°C – 5% CO2 – 95% RH – “Optimal” conditions for many, but not all, applications – “Optimal” is contextual • “Optimal” depends upon the requirements of the system being studied – Psychrotrophic / thermophilic bacteria have different temperature requirements • “Optimal” depends upon the aim of your research – Healthy vs. stressed systems (e.g., to mimic dehydration, manipulation of RH is required)
- 5. What You Will Learn How to tell if your CO2 incubator provides active humidity control How to prevent condensation, even at high humidity Whether you can trust that your CO2 incubator really provides 95% RH
- 6. DOES YOUR CO2 INCUBATOR PROVIDE ACTIVE HUMIDITY CONTROL?
- 7. Types of CO2 Incubator Controls • Open Loop Controller – Without programmable RH – With programmable RH • Closed Loop Controller (programmable RH is standard) Do any of these provide active humidity control?
- 8. Open Loop Controller Without Programmable RH Control Programming (ONE set point) Heat Water Pan Humidity Delivered to Chamber
- 9. × One humidity set point determined by manufacturer, not user × Microprocessor uses mathematical formula based on static (not real- world) conditions × Uncertainty – is system delivering promised RH? Control Programming (ONE set point) Heat Water Pan Humidity Delivered to Chamber Open Loop Controller Without Programmable RH
- 10. Does it provide active humidity control? × No control over relative humidity whatsoever Open Loop Controller Without Programmable RH
- 11. “Dial in” to set point Heat Water Pan Humidity Delivered to Chamber Open Loop Controller With Programmable RH
- 12. User-defined humidity set point × Microprocessor uses mathematical formula based on static (not real- world) conditions × Uncertainty – is system delivering promised RH? “Dial in” to set point Heat Water Pan Humidity Delivered to Chamber Open Loop Controller With Programmable RH
- 13. Does it provide active humidity control? × Only gives the illusion of control Open Loop Controller With Programmable RH
- 14. Open Loop Controllers – The Problem No System Feedback
- 15. Closed Loop Controller “Dial in” to set point
- 16. Closed Loop Controller “Dial in” to set point User-defined humidity set point Control algorithm adapts to real- world conditions Certainty – system maintains RH to set point
- 17. Closed Loop Controller Does it provide active humidity control? Yes
- 18. HOW CAN YOU PREVENT CONDENSATION, EVEN AT HIGH HUMIDITY?
- 19. Is Condensation Completely Avoidable? × No Some condensation is unavoidable, such as when cooling the chamber interior
- 20. Is Condensation Preventable? Yes During normal operation, condensation is preventable, even at high humidity
- 21. What Causes Condensation? Water condenses from the air onto a surface when the temperature of the surface falls below the dew point
- 22. What Causes Condensation in a CO2 Incubator? • Fluctuation in environmental parameters (e.g., door opens) • Interior surface temperature gradient changes – Surface temperature gradient: Variance in temperature across the interior surface, expressed as a range of temperatures • Portion of the surface temperature gradient falls below dew point • Condensation occurs
- 23. Technologies that Prevent Condensation? × No prevention above 90% RH × Designated “cold spot” in incubator cooled to below dew point to “divert” (not prevent) condensate – Does not prevent condensation from occurring on other surfaces that are at or below the dew point • Closed-loop controllers provide better control over air temperature & RH, which directly affect dew point, but this is not enough
- 24. Muddled Marketing Claims Incubator suppliers are not being untruthful when representing the level of control they are able to provide over RH and condensation… …but they are not telling you the whole story. The most pervasive claim about CO2 incubators may be the least understood.
- 25. DOES YOUR INCUBATOR REALLY PROVIDE 95% RH?
- 26. RH Sensor Accuracy • Closed-loop controllers in CO2 incubators typically use a capacitive RH sensor to provide feedback to system • Like all instruments, subject to some degree of inaccuracy • How accurately the incubator control algorithm maintains RH set point directly depends on the accuracy of the RH sensor
- 27. RH Sensor Accuracy Accuracy of capacitive RH sensors depends on: • Temperature • RH • Length of time in continuous operation • Age of instrument × Most incubator manufacturers do not disclose this information, let alone account for it in the control algorithm
- 28. Typical RH Sensor Accuracy Conditions RH Sensor Accuracy RH is between 10-100% @ 25°C ± 1.8% RH is greater than 80% for 60 hours Additional + 3% Temperature is between 10°C and 35°C Additional ± 0-1% Temperature is greater than 35°C Additional ± 1-2% Yearly Drift Additional < + 0.5%
- 29. Real-World Implications • An RH sensor performs least accurately under the most common conditions • An incubator in its first year of use, in continuous operation at 37°C and 95% RH may be delivering humidity levels as low as 88.2% and as high as 98.8%.
- 30. Real-World Implications The verdict? × Uncertainty – impossible to tell whether the system is maintaining anywhere near the RH set point Unless sensor accuracy is factored in to the control algorithm
- 31. TECHNOLOGIES TO LOOK FOR AND INSIST UPON
- 32. Humidity & Condensation Control Technologies Closed-loop control algorithm • Allows user-defined, active humidity control, reducing experimental error and uncertainty • Helps prevent condensation by providing better parameter control Two humidity set point ranges 1. “Up to 90%” where user can “dial in” to a desired RH 2. “90%-95%” where a “sweet spot” of >90% RH can be delivered consistently • Prevents condensation and the risk of contamination that goes along with it • Significantly reduces uncertainty pertaining to RH accuracy
- 33. Thank You For more information on this topic, download our white paper: http://info.bakerco.com/co2-incubator-humidity-control