Using CO2 sensor to measure humidity

For my graduation project I am looking for a (cheap) sensor which measures CO2 and humidity and I stumbled upon the thread below via Google:

http://forum.arduino.cc/index.php?topic=55956.0

In this thread someone mentions it might be possible to measure the CO2-level using only an humidity sensor by using the formula:

C6H12O6 (glucose) + 6 O2 => 12 H2O + 6 CO2

I am no chemic (nor a programmer), but I was wondering whether this would actually lead to usable values? And if it is also possible the other way around (measure H2O with a CO2-sensor)?

The sensor will be used to measure indoor air quality and will provide tips for (manual) ventilation. I am a product designer so I will need to hire someone else to build this sensor for me, but before proceeding I was wondering about the above. Thanks in advance!

iljoesjin:
For my graduation project I am looking for a (cheap) sensor which measures CO2 and humidity and I stumbled upon the thread below via Google:

Precalibrated CO2 sensor - Sensors - Arduino Forum

In this thread someone mentions it might be possible to measure the CO2-level using only an humidity sensor by using the formula:

C6H12O6 (glucose) + 6 O2 => 12 H2O + 6 CO2

That was me :slight_smile:

(after 2.5 yrs extra thinking about it)
The assumption in that thread was that in a bedroom (closed windows) people are breathing out H2O and CO2 in a more or less defined ratio (by burning sugar).
In theory the amount of H20 should therefore be an indicator for CO2.
However in practice when the amount of H2O vapor is maximized the RH is 100% (and water will condensate) but the CO2 will still increase.
So this way of measuring only has a chance of working if the RH 100% is not reached.

Still, I think it is worth to investigate if a relation can be found, and how the formula looks. This is a project in itself.

Humidity is not easy to measure, the DHT11 and DHT22 often discussed here are only indicative +-5% (or worse)
I would advise to look at e.g. - SparkFun Humidity Sensor Breakout - HIH-4030 - SEN-09569 - SparkFun Electronics -

hope this helps,