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FAQs about IEQp1 :

We have a VAV system where single AHUs serve multiple zones. Do we need to take outside air measurements at each VAV box?

What if after our Preliminary Review we have to re-work the ventilation rate procedure calculations and find that we need to make corrections to the system in order to meet the prerequisite? Can we redo the outside air testing after making corrections? Wo

What if our systems do not meet the required outside air when systems are tested at worst-case conditions?

Our building has a single fan that supplies outside air to multiple AHU’s. Do we need to perform outside air testing at the supply fan or at all AHUs?

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EBOM-2009 IEQp1:Minimum IAQ Performance

CO2 measurements

Hallo, In our project there are AHUs providing a mix of outdoor and return air. Due to the machine room layout, it is very difficult to measure outdoor airflow (cfm). There is a formula to calculate outdoor air supply using: -outdoor air supply (cfm) -CO2 levels in supply duct (ppm) -CO2 levels in return duct (ppm) -Outdoor CO2 levels (ppm) Does anyone have experience having this prerequisite approved with this method?

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Ben Stanley
Senior Sustainability Manager
WSP - Built Ecology
LEEDuser Expert
188 thumbs up

Wed, 10/26/2016 - 20:10

Hi Gustavo, I haven't seen that formula used before but there is another method to approximate the OA flow based on the temperature of outdoor, mixed, and return air temperatures when the supply flow from the AHU is known. See section 7.6.3.3 in ASHRAE 111-2008. The trick however is that the approximation is only considered to be accurate if there is a temperature difference between 25 - 50 degrees between the outdoor air and return air temperatures.

Thu, 10/27/2016 - 18:27

Thanks! I didn't know this method. Actually the formula is very similar to the one measuring CO2 levels. I read it in one of the I-BEAM text modules and it is only is accurate if there is a difference of more than 200 ppm in each air stream.

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