Carbon dioxide sensors

[vijay_study]

Hi,

We are using CO2 sensors for Demand controlled ventilation in one of the office area conference rooms.

System is being catered by chilled water type cassete units. (Chiller water entering temperature to cooling coil 7°C)

CO2 sensors are being used to control amount of ambient air being introduced inside the rooms based on occupancy of the room.

Wanted help on set points in PPM for full occupancy.

Thanks

Vijay Kumar

[Abby Normal]

to control body odurs and to keep up with metabolism, you are supposed to aim for keeping CO2 levels less than 700 PPM above the CO2 level in the fresh air.

So if it was rising up over 80% of that threshold I would start bringing in more air.

Now a lot of thought has to be put into the quality of the fresh air, whether you have a building full of hypochondriacs who are allergic to everything, and even, 'did they build the building out of materials that off gas and irritate people'

I suggest you look through ASHRAE 62.1 2007 edition, they will let you view it online for free at ashrae.org

[vijay_study]

Hi Abby,

Thanks for the reply.

We have gone through ASHRAE 62.1 2007 edition. We have worked out fresh air requirement also based on specified procedures.

Fresh air requirement at full occupancy works out to 550cfm. However, base minimum fresh air load works out to 110cfm.

So essentially we need to modulate between 550cfm & 110cfm. So CO2 ppm level shall be range for this difference i.e. 700PPM = 440CFM (550 - 110)

I hope i am not confusing.

Whats your opinion on above.

[Abby Normal]

telaire will make a control that can send signals to modulate or something as simple as a relay to go from a minimum position setting to a wide open setting on the fresh air.

I was thinking something simple. If your ambient CO2 was around 450 PPM and you were shooting to limit the indoor air to 1150 PPM, have the control open up at around 920 PPM, and close back down to minimum position when it drops a couple hundred or so.

Or you could use the modulating approach and try and have it hold a setpoint level.