ASHRAE 62 30% increase as it relates to EAc1

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I'm having a tough time deciphering how the USGBC wants you to prove a
30% increase in OA (versus ASHRAE 62) for multi-zone systems, and how
this impacts the energy model for the proposed building.

There is a very specific way to determine the volume of outside air for
a multi-zone system (VPR using the 62MZCalc spreadsheet). This takes
into account, among other things, room area, population, supply volume,
minimum primary air volume, efficiency of transfer air, system
efficiency, etc. Once you understand all of the variables, it's fairly
straightforward to prove compliance with EQp1, and obtain the minimum OA
intake volume.

However, EQc2 requires a 30% increase in outside air volume for EACH
zone "above the minimum rates required by ASHRAE Standard 62.1-2004 as
determined by EQ Prerequisite 1". Although I've received USGBC comments
before claiming that I have to prove that EACH zone has 30% more OA than
required by the VPR, can anyone confirm for sure if this is the case for
multi-zone systems?

To give you an example:

I've got a 33,000 square foot floor served by an AHU. Standard office
space with 3 or 4 conference rooms. I've used the 62MZCalc spreadsheet,
and determined that my AHU needs 3,800 CFM OA. I've *designed* the
system to provide 7,000 CFM. Almost twice the amount of outside air as
needed (I have DCV in place). However, the critical conference room
doesn't get even the minimum required OA. It doesn't need to - that's
the whole point of the Multizone calc, and a good reason to use series
fan-powered terminals.

Per the NCv2.2 Reference Guide, we are supposed to include the actual OA
volumes in the energy model, so I guess it's important to get this
right, especially for those clients that request a 30% increase.

Thanks in advance,

James Hansen, PE, LEED AP

James Hansen's picture
Joined: 2011-09-30
Reputation: 200

And the whole thing gets even more complicated if you want to pursue
this credit in combination with the credit for Outdoor Air Delivery

Not to mention the conflict of whether you do or do not have to claim
the added energy cost in credit EA-1 associated with 30% increase in

Michael Tillou, PE LEED AP

Michael Tillou's picture
Joined: 2011-10-02
Reputation: 0