×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Demand Control Ventilation using CO2 Sensors

Demand Control Ventilation using CO2 Sensors

Demand Control Ventilation using CO2 Sensors

(OP)
I'd like to get some feedback from folks on the use of CO2 sensors to increase outside air delivery to a building.  I know the theory is romantic but is the application effective?  I keep hearing negative comments about the sensors going out of calibration, long response times, etc.  What feedback do you guys have?
Thanks
Grizzly

RE: Demand Control Ventilation using CO2 Sensors

Grizzly,

Most CO2 sensors use non-dispersive ifrared (NDIR) detection. From my own experience, these sensors are significantly affected by barometric pressure. NDIR sensors that I calibrated in Reno at 1,000 ppm all read 1,300-1,400 ppm when we got to Stockton, some reduced (3,000-4,000 ft) altitude later. Imagine what a 35,000 ft altitude plane ride does.

They need to be zeroed and spanned after installation - forget the factory calibration.

From there, I would recommend running a zero and approx. 1,000 span gas at least monthly through the sensors, adjusting the zero and span setscrews as needed.

Assuming you can maintain this type of regimen, CO2 sensor use can be effective for areas with intermittent, heavy occupancy. This includes classrooms, theaters, cafeterias, gyms, and auditoriums. I would not use CO2 control in high air exchange buildings such as labs and hospitals, because the levels wouldn't typically exceed 200-300 above ambient.

I hope some of this helps. Best regards, -CB

RE: Demand Control Ventilation using CO2 Sensors

Hi Guys,

Chasbean identified a common problem.  Calibration is very dependent on pressure (altitude).  The lower the pressure, the fewer atoms of CO2 in the optical chamber, thus the ppm reading will be lower at higher altitudes and higher at lower altitudes.  The more feature-packed units have a simple altitude adjustment nowadays, though, so it's easier to compensate.

Most manufacturers are offering three-to-five year calibration guarantees.

If you have a variable occupancy, I'd go for it.

DRWeig

RE: Demand Control Ventilation using CO2 Sensors

As all of the comments are basically true there seems to be a solution to the problem of calibration and aging. The "duel beam" on NDIR is one method of compensating for changes to the sensor optics resulting from aging and partical buildup. As far as drift goes an approach is to have the sensor calibrate itself on a nightly basis when the space is unoccupied, and inside levels drop to base line outside levels. Studies have determined over 3 years of of operation of 3 sensors using a nightly automativ baseline calibration that sensor accuracy remained well within 50ppmover the duration of the test.ASHRAE JOURNAL, 2/2001 Mike Schell, Dan Int-Hout.

vita non est vivere sed valere vita est     "life is more than merely staying alive"

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources