[Bldg-sim] ASHRAE 62.1

David Yuill dyuill at cox.net
Fri Mar 27 10:14:22 PDT 2009


Robert,

I haven't seen any replies to your Std. 62.1 question, so I'll assume you're
still wondering.  

The standard calculation of the required outdoor air (OA) amount already
includes population diversity, which typically reduces the total OA
required.  So, to your question:  yes, diversity can be used to reduce
system OA requirements (and is a normal part of the Std. 62.1 calculation).
Diversity is calculated with equation 6-7, and it's factored into the total
uncorrected OA intake amount in equation 6-6 (referencing 62.1-2007).

If you're correctly using the standard for a system that serves multiple
zones and uses some recirculated air, you will have calculated which zone is
the critical zone: the that zone needs the greatest fraction of primary air
at the ventilation design condition.  (Note that the ventilation design
condition is not the cooling or heating design condition, necessarily).  The
critical zone drives the total OA requirement.  All other zones
automatically get the required OA allotment or more.  

To know which zone is the critical zone, look at Appendix A.  There's a
section called "Selecting Zones for Calculation".

To your comment "every room with only one person gets the required OA
allotment", note that every zone has a population AND an area component to
the required OA.  

There are ways to meet the standard and reduce the total OA required.  These
generally involve changing the critical zone until it becomes non-critical
(the next most ventilation intensive zone becomes the critical zone).  This
can be done with a transfer air fan (bringing air from an over-ventilated
zone to reduce the required primary air in the critical zone), or by
increasing the minimum VAV flow setting on the critical zone (this zone may
use more reheat energy, but this can be offset by the cooling energy saved
by reducing the total OA, for example).  It depends on your particular case.

If that doesn't answer your questions, feel free to email me off-list.



David Yuill, P.E.
Principal
==================
Building Solutions, Inc.
3315 S. 96th Street
Omaha, NE 68124
402-556-3382
bsiengineering.com
==================

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of RobertWichert
Sent: Wednesday, March 25, 2009 2:24 PM
Cc: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] ASHRAE 62.1


I posted an ASHRAE 62.1 question to this list a few days ago.  I have 
made a lot of progress since then, but there are still a few nagging 
questions.  I know that ASHRAE 62.1 is not a primary focus of this list, 
but I hope that some of you LEED gurus out there will help me out.

Basically I am looking to find out if population diversity can be used, 
across the board, to reduce the system outside air requirements in 62.1 
and if you can do that, how do you document room-by-room compliance as 
required by LEED Existing Building requirements?  My thoughts right now 
are to use population diversity to reduce the entire system OA 
requirement, but to check that every room with only one person gets the 
required OA allotment.

This is perhaps more strict than necessary.

All ideas are welcome, but if somebody is an ASHRAE 62.2 guru, I 'd love 
to correspond off-list on this.

Cheers!

 

-- 
Robert P. Wichert, P.Eng.
+1 916 966 9060
FAX +1 916 966 9068




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