Installing CO2 devices in non-densely occupied spaces

Fabiano - very interesting question! You could pose this to GBCI in a CIR. While this approach would technically meet the credit's stated intent, I do think that this credit was written to encourage the use of AHU OA measuring devices. These devices can validate the systems ability to deliver the proper amount of OA to a bldg. While a C02 sensor would ensure enough ventilation air is reaching a space it would not easily be able to tell you if too much is being delivered. We had a project where the OA damper was improperly sized and too much ventilation air was being delivered, even at the minimum open position. There is a large energy penalty for conditioning too much OA on the coldest and hottest days of the year. We wouldn't have know there was a mistake without the air flow sensing devise. Thus your alternative approach may be a risky venture. In addition, cost wise, several extra CO2, controls, etc would seem to be more expense than one outdoor air flow measuring station.

Hi Fabiano, I agree with Dylan. CO2 sensors in non-densely occupied spaces will not meet the credit requirements. As an aside if you want to use CO2 sensors to determine if the ASHRAE 62.1 minimum outdoor air is being supplied to ALL spaces, you would have to put a CO2 sensor in each space. A common mistake some project teams make is putting a single CO2 sensor in the return air from multiple spaces and controlling to this. That design does not meet ASHRAE 62.1 requirements and will not ensure the proper outdoor air is delivered to each space. One final note, ASHRAE 62.1-2010 requires direct measurement of outdoor air in variable air volume systems.

Fabiano - we have had success with the proposed approach - CO2 sensors in all densely and non densely occupied spaces.

Webly, could you explain how you convinced the reviewer with CO2 sensors in all densely and non-densely occupied spaces?