SIngle 100% outdoor air AHU is serving multiple zones (through diffusers) on couple of floors in a highrise office building. When filling the Minimum Air Quality Performance Calculator, which values should we input in the "Zone Outdoor Airflow Provided" column? We don't have measured values for each zone, as we are taking the measurement only at the system level, i.e. at the AHU itself.
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Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
528 thumbs up
March 2, 2017 - 8:58 am
Since the AHU serves multiple zones, you should complete the 'Multiple zone' tab of the Minimum IAQ Performance Calculator.
The 'outdoor air provided' is the measurement taken at the 100% outdoor air unit if this air handling does not serve other air handling units.
IF, the 100% outdoor AHU serves other air handling units, fan coils, heat pumps, etc. then the air handling units, fan coils, heat pumps are considered to be the system level, hence each requiring outdoor air measurements.
Hope this helps!
Rasita Masalskyte
MsVesta Consulting
5 thumbs up
March 2, 2017 - 9:40 am
Dave,
As the system is 100% OA system serving many different zones in the building shouldn't we select the "100% Outdoor Air Systems" tab? If I select "Multiple zone" tab instead, it asks me to fill different values related to recirculated airflow which isn't applicable in our case.
There are no additional AHUs or fan-coils, the main AHU is serving fresh air directly through ducts. So we have this one measurement at the AHU. But in the Calculator tab we list dozens of various zones with no actual measurement - so what do we input in the last column "zone outdoor airflow provided" next to each and every listed zone?
Rasita
Dave Hubka
Practice Leader - SustainabilityEUA
LEEDuser Expert
528 thumbs up
March 2, 2017 - 10:35 am
HI Rasita, you are correct.
The 100% OA system tab is the most applicable tab for the project you are describing. On past projects we were successful using the multipe zone tab for 100% OA units serving multiple zones....but the USGBC calculators have been updated since then. My apologies for complicating things.
Regarding "what should be input in the last column 'zone outdoor airflow provided'"....this is an issue we discussed with the top folks at the USGBC. First of all, USGBC confirmed that they do not require a complete test and balance of the mechanical systems to determine the airflow into each room/zone. That said, there should be some engineered guess to the amount of airflow expected to be supplied to each zone, for example, if a 10 inch round duct supplies air to a room it could be expected that the rooms "zone outdoor airflow provided" = 400 cubic feet per minute.
So you may need to review the mechanical plans or perform an onsite inspection to determine the size of ducts to each room.
thanks for your patience!
Rasita Masalskyte
MsVesta Consulting
5 thumbs up
March 3, 2017 - 5:27 am
Thanks Dave!
We have about 45 AHUs, each serving dozens of different zones, more than 330,000 sf area in total, so a lot of rooms and lots of guessing..
But I see what you are saying. Mechanical plans may be too old, as many tenants have changed layouts through years of building operation. Onsite inspection can be a hurdle, but as I understand there are no more alternatives. Thanks again!