eCO2 to detect human presence - ZMOD4410

dear team,

thanks for a very promising product. I've been evaluating for several month. my target is to detect human presence based on CO2/eCO2.
Accordingly the application will activate diffrent HVAC settings.

i'm getting values from the ZMOD4410 in a small / home office.

The values are evolving with time. however i'm not getting a correlation between human presence (day and evening) and eCO2 / IAQ.

For example eCO2 will be high during nights although there is no presence or relatively constant. I am practically breathing into the sensor (.8m distance)

enclosed is typical data for 24h

eco2 24-hours

I know the eCO2 is an estimation based on TVOC and relative increase.
I cannot reproduce the results described in the application note estimation CO2

is there a mode or recommendation where the human presence in a room can be estimated reliably?

  • Hi Ramus,

    Thank you for reaching out to Renesas Engineering community and showing interest in Renesas Electronics Pvt Ltd. I have a couple of questions, so that we would better understand your situation.

    How long were the sensors in operation before this measurement?

    Did you use a ZMOD EVK or is it your own implementation with the ZMOD firmware and please mention the version of EVK or the downloaded firmware package?

    Generally, we recommend:

    Run the sensors for longer (few days) with the latest firmware & algorithms. Record the raw resistance data (rmox) and share the with us.

    By enabling the advance eco2 algorithm, we can quickly check it in our EVK. Advanced (=standard) eCO2 only follows slow VOC changes to exclude artificial, fast VOC changes. Having this deactivated it will follow ALL VOC changes (e.g., blowing on the sensor). For more information (documented on page 9 bottom) please go through the following link.

    If anything is not clear, please feel free to ask.



  • Thanks for detailed answer.

    I did not know there was an EVK. We have developed before the EVK was available.
    The chip used for the are prototypes are custom PCB but we also have one US082-1

    The FW is 3.1.0 as checked from iaq_2nd_gen.h.
    I see there is a 3.2.0 and I will upgrade to benefit from improvements.

    I need to use the advanced algorithm which gives the best correlation to actual CO2 to exclude artificial TVOC.
    and hence reflect the actual occupancy of the room / space.
    I do not need immediate response of CO2 (blowing case).

    According to advice, I will log the rmox values coming every 3s (it will be a relatively large file),
    in sample format below:

    *********** Measurements ***********
     Rmox[0] = 892682.94 kOhm
     Rmox[1] = 81489.90 kOhm
     Rmox[2] = 13374.55 kOhm
     Rmox[3] = 3054.26 kOhm
     Rmox[4] = 867.15 kOhm
     Rmox[5] = 290.24 kOhm
     Rmox[6] = 118.05 kOhm
     Rmox[7] = 317.00 kOhm
     Rmox[8] = 989.09 kOhm
     Rmox[9] = 3853.54 kOhm
     Rmox[10] = 19852.08 kOhm
     Rmox[11] = 145142.16 kOhm
     Rmox[12] = 2499895.81 kOhm
     log_Rcda = 5.08 logOhm
     EtOH = 0.01 ppm
     TVOC = 0.02 mg/m^3
     eCO2 = 530.03 ppm
     IAQ  = 1.00

    The previous results were coming from a sensor running since May 26, about 4 months.

    kindly confirm that format above is usable.

    thanks in advance