[Bldg-sim] DOAS and baseline OA

[Anne Juran]

Paul - I took the same approach, and my LEED reviewer shot it down.  I
didn't explain it, though, so that may be why.  Have you had success with a
LEED review and your approach?  If so, did you have to explain it or did you
just provide the calcs that prove it?  Thanks!

 

 

From: Paul Riemer [mailto:Paul.Riemer at dunhameng.com] 
Sent: Tuesday, August 16, 2011 9:38 AM
To: 'Michael A. Eustice'; 'Jim Dirkes'; 'Anne Juran';
bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] DOAS and baseline OA

 

Michael alludes to the system ventilation efficiency (E_v).  Per ASHRAE 62,
It and the zone air distribution effectiveness (E_z) vary based on system
configuration. 

When ASHRAE 90.1 says the minimum outdoor air must match I take that to mean
the base R_p and R_a values not necessarily the resultant V_ot values.
Similarly when LEED says DCV must be compared against the minimum ASHRAE
values I take that to mean R_p and R_a values as well.

I assert that it is appropriate to calculate separate E_v and E_z values for
the each system in baseline and proposed models, which  can lead to ASHRAE
62 multi-zone calculations for the baseline systems.

 

Paul Riemer, PE, LEED AP BD+C 

Associate / Mechanical

DUNHAM

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Michael A.
Eustice
Sent: Tuesday, August 16, 2011 8:19 AM
To: 'Jim Dirkes'; 'Anne Juran'; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] DOAS and baseline OA

 

The critical zone fraction as explained by ASHRAE 62.1 will, in most cases,
increase outside air intake in a VAV system.  This is due to the need for
the entire system to increase its outside air fraction if one zone's airflow
dips to its minimum VAV airflow.  To maintain the ventilation fraction in
the one zone that reduced airflow, the entire system ingests large amounts
of outside air to make sure it gets enough air to that particular zone.

 

It's a bit more complicated than that, but that's the simplest explanation.
There are ways around it, but it takes time to 'correct' for small, high
ventilation-fraction areas that tend to drive the system towards high
ventilation rates when they modulate to minimum position.

 

Hope this makes sense.

 

Michael  

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jim Dirkes
Sent: Tuesday, August 16, 2011 9:12 AM
To: 'Anne Juran'; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] DOAS and baseline OA

 

Dear Anne,

I'm not sure why you think the OA requirement varies by system.  I'm not
well versed in Standard 62, but my basic understanding is that one of the
calculation methods is the result of building area and number of occupants.
Those are unchanged by system selection . which is why it makes sense for
Appendix G to require matching volumes.

 

The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Anne Juran
Sent: Tuesday, August 16, 2011 8:33 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] DOAS and baseline OA

 

I'm curious how everyone is handling the OA for Appendix G simulations when
using a DOAS in the proposed system.  We have a design that is DOAS + FCU
with a  total OA of 8,000 CFM.  When you run the OA calcs for this same
building with a VAV system (the baseline), the total OA required to meet
Standard 62 is 39,000 CFM.  This difference in OA represents a significant
energy savings (in climate zone 4A), yet Appendix G requires the OA volumes
to match.  It does not seem "fair" to me that the proposed case cannot take
credit for design choice when it comes to OA.  I feel like Appendix G should
make an exception for DOAS.  Am I missing something?  Is there a way around
this?  Any thoughts are appreciated!

 

Anne

 

 

 

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