[Bldg-sim] ASHRAE 62 30% increase as it relates to EAc1

[James Hansen]

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,

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

www.ghtltd.com <http://www.ghtltd.com/> 


The information contained in this communication is confidential, may be privileged, and is intended only for the use of the addressee.  It is the property of GHT Limited.  Unauthorized use, disclosure or copying of this communication or any part thereof is strictly prohibited and may be unlawful.  If you have received this communication in error, please notify me immediately by return e-mail or by e-mail to ght at ghtltd.com, and destroy this communication and all copies thereof, including all attachments.  Thank you.



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