Heat-triggered sensors vs. CO2-sensors

Hi Emil, this approach would work for CI v2009 EAc1.3 to meet the requirement to install active controls capable of sensing space use and modulating the HVAC system in response to space demand. However, the requirements for this credit are pretty stringent regarding CO2 sensors.

You could request in your submittal that LEED Interpretation 5731 be considered for alternative compliance (the Applicability tab indicates that it hasn't been considered for 2009 projects yet, but also that it hasn't been marked as 'not applicable'). This LI allows an alternative to providing CO2 sensors in areas where 100% outdoor air is provided: "The primary intent of the credit is to provide indoor air quality monitoring to sustain long-term occupant health. Your project's HVAC system is intended to provide the maximum outside air volume, but would require some instrumentation to report on the resulting IAQ conditions to capture the point. CO2 sensors per se may not be required, but a monitoring system for the lab spaces should provide feedback in a form that affords operational adjustments. By providing a monitoring system that can give feedback on the space ventilation performance, operational adjustments (to outside air volumes, air changes, mixing boxes, distribution etc., either automatic or manual) can be made to correct problems."

A project-specific CIR may be the best option.

Emil, it sounds like you are proposing utilization of a 100% OA multizone VAV system in lieu of monitoring CO2. Modulating space airflow based on temperature is a good idea and is very common but it does not replace CO2 monitoring. I do believe you will need to provide CO2 sensors to achieve this credit. Furthermore, there is no requirement that the ventilation rate must be changed in response to the space CO2 level, only that an alarm is generated if it is 10% low or more. I hope that helps. Also, just as an aside, if you have non-densley occupied spaces and are using a 100% OA VAV system you can use the VAV flow rings to monitor the ventilation air flow and simply program the alarms. That will save money on purchasing a system total AMS.

Hi,
I've the same questioning about the CO2 sensor with 100% OA system multizone VAV, but my client would like 6 air changement per hour.

If the minimum outside air flow (6*volume*100%) is greater than the OA flow from the ASHRAE calculation (Vbz) is it possible to avoid the CO2 sensor in these specific zone?

Thx, Cédric

If it is a densely occupied space then it requires a CO2 sensor. If you are maintaining 6 ACH then you probably qualify for Increased Ventilation Credit. Having the 100% OA unit does not exempt you from CO2 sensors according to USGBC.

Just a reminder that the CO2 sensors do not need to be tied into the HVAC system. An audible or visual alarm to the occupants is all that is needed.

Hi, thx for the answers.

I understand that the CO2 sensor is used to detect VAV box troubles too.

But in case the VAV box has a flowrate sensor which is connected to the HVCA system (6 ACH@ 100 % OA) for the detection of flow instabilities, is the CO2 sensor necessary?

It is still required to obtain IEQc1