Indoor Air Measurements

Hi Gustav, On February 2019, we asked the GBCI the following question: About the CO2 and TVOC readings: which and how many locations do we need to read?
GBCI answered: Thank you for contacting GBCI. As LEED v4.1 is in a Beta phase, when conducting the IAQ testing, project should adhere to the requirements available at the time of the testing. Refer to the EQ Prerequisite: Indoor Environmental Quality Performance for currently available requirements within the LEED O+M Guide (https://www.usgbc.org/resources/leed-v41-om-beta-guide). At this time, the LEED v4.1 rating system does not currently include a minimum number of testing locations. The guidance does state the following:
"Take the indoor air measurements in locations representative of all occupied spaces, within the breathing zone (between 3 and 6 feet (900 and 1800 millimeters) above the floor), during normal occupied hours, under typical minimum ventilation conditions." As such, the testing locations do need to be representative of all occupied spaces. It is common for teams to include a testing location on each floor of the building. Project teams should provide the Indoor Air Quality evaluation report, including a narrative explaining how test locations were determined, time and dates testing was performed and floor plans highlighting test locations.
 

The feedback I receive from our IAQ engineers is that each location point in the building must be tested three times, and at least 30 minutes apart.  So if a building is 100K SF, at least 4 points must be sampled ( 1/25K SF), each three times (totaling 12 total samples), and at least 30 minutes apart at each unique sample location in the building (so points 1-4 would be tested 3 times each).  This was also supported by Greywolf who sells IAQ testing equipment.  After a lengthy review of LEED reference material and the various iterations of LEED Credits referreing to IAQ testing for both NC and EB, I cant find specific guidance about the frequency, nor the length of time between samples.  In fact they seem to explicitly rely on the testing agent to determine this.  I assume this is to get an average per location, but the LEED guidance doesnt seem to specifically require this, at tleast taht I can find.  Can anyone support or reject the suggested testing intervals I am referring to? how different can each sample be form the one before it? If we are averaging it anyway, wouldnt we see typical regression the more samples we take? I feel like an engineer overthinking this, I just wantt o do whats most effective... the number of sample in a 1.7M SF building is substantial!