We have 50+ buildings and are looking at standardizing our brand and type of CO2 sensor. We currently have multiple brands/types (many of which need replacement or calibration). Moving forward, we would like to stick to one brand/type as this would make the replacement and/or calibration process a lot easier. In your opinion, what are the best CO2 sensors in regards to value (cost vs. performance), lifespan, warranty, ease of calibration, length of time between calibration etc. I would also like to know what the general life expectancy of a CO2 sensors are? Which brands provide longer life expectancies? How long before most CO2 sensors need to be calibrated? Which brands seem to need less calibration over time? 90% of our CO2 sensors are duct mount. The signal can be either 4 to 20 mA or 0 to 10 VDC and an accuracy of +/- 100 PPM will do.
* Any mA or VDC signal will work.
Sense-Air makes a very high quality device. Many brands out there today (Veris, Senva, etc) use the sensor element from Sense-Air, so not a bad idea to go to the source itself.
Check out http://www.qelsafety.com/ they are in Ontario , good product and service
also checkout greystone energy, they make a tough sensor.
Well, I am hardly familiar with all possible CO2 sensors one might buy and use.
Originally Posted by pare
I have used a LOT of two of the specific lines mentioned here. The QEL and the Veris units. (Veris both under their name and units which are Veris but with someone else's name on them.)
Have also used Telaire, Vaisala, Vulcain, etc. But in far fewer numbers.
I've also used some others I won't name, since my experiences with those were less than pleasant.
Either QEL or Veris seem to be good products. Between the two I've got probably at least a couple thousand out there chugging along and working fine. We tend to use more Veris than QEL. For a combination of reasons. (1) We get a substantial discount on those units, and they are somewhat easier to work with in regards to installation. At least our installers think so. They're not too fond of the cramped working space of the QEL units. But the QEL units work fine, in my experience, so I don't think you'd go wrong with them if they become your choice.
In any event, some notes from me. Only my opinions, don't take it for more than that. But I've worked with a LOT of installed CO2 sensors.
NDIR type sensors are the most common. (Non-dispersive infrared) The one poster is correct, Senseair makes a key component used by many manufacturers of HVAC service CO2 sensors. That's the K30 NDIR module. Senseair also developed and patented ABC logic. The combination of the two technologies seems to work well.
NDIR type sensors seem to me, in my experience, to be more resistant to going bad quickly due to pollutants in the air, etc. Tho you don't want people spraying a lot of stuff around them which might pass though the sensor chamber.
The ABC logic (Automatic Background Correction) does work pretty well. That logic might be called by other names depending on the manufacturer. The idea is that the unit keeps a record over a period of several days (usually a week) of the lowest reading recorded. Then compares that to factory calibration settings, assuming a baseline of 400 ppm CO2 as average low ambient, and adjusts itself accordingly. Certainly this isn't perfect. But in live tests over years duration I've seen units using ABC logic, or a variation thereof, stay much closer to a real, accurate CO2 reading than other units without said logic.
Drift over time in the readings can cause you to either under ventilate a building, or ... more often ... to over ventilate. Thus wasting energy by having to condition excess outside air.
Again, I'm talking real experience. For instance I have records for 2 large school districts for whom I do routine, regular calibration checks. That's covering hundreds of CO2 sensors, of several types, with some having been installed 15 years ago, and some of more recent vintage.
How often to do a calibration check?
Some manufacturers suggest once every 5 years is enough, some suggest as often as once a year.
I think an actual test, with accurate, currently certified handheld device and a supply of calibration gas once every 5 years is sufficient. Especially if you're using ABC logic. This is expensive in time. Takes about 15 minutes per unit, not counting just finding and getting to the unit.
But the building maintenance people should more often just observe the readings from each (they usually ignore them unless an alarm is set off or something) to look for problems. Perhaps just have their automation system record the daily high and low, over time, and check record once every 6 months or so, to see if one is trending ever higher, or is really out of whack when compared to other units. Keeping in mind you can have spikes in the readings time to time due to all sorts of reasons.
Also handy if you have an outdoor CO2 sensor so you have a record of what actual ambient is. It can vary a LOT from location to location, by time of day, by season, etc.
Life expectancy? Shrug, I have units of the type I mention which have been chugging along for 10-15 years. Still there, and last time checked they where within acceptable accuracy. That's within 100 ppm of readings as compared to NIST certified unit withing current calibration. On average, for units I mentioned with ABC engaged, I might have to re-zero a unit once every 10 years. There are some exceptions due to unit being in excessively polluted or dirty area.
One note about ABC logic. The logic presumes that at least once each day a space will be unoccupied for some period of time and will assume a CO2 content the same, or nearly so, as outdoor ambient. For spaces that are always occupied ABC logic doesn't work very well. Better to leave it OFF for such spaces.
Units like the Veris can do 4-20 ma, 0-5 VDC, and 0-10 VDC.