[Bldg-sim] DOAS and baseline OA

[Jason Glazer]

Just to give some perspective on how ventilation will likely 
be handled in future versions of LEED. Here is the text from 
the 90.1-2010 section on ventilation.

Jason

----------------------

G3.1.2.6 Ventilation. Minimum ventilation system outdoor air 
intake flow shall be the same for the proposed and baseline 
building designs.

Exceptions:

a. When modeling demand-control ventilation in the proposed 
design when its use is not required by Section 6.3.2(p) or 
Section 6.4.3.9.

b. When designing systems in accordance with Standard 62.1 
Section 6.2 Ventilation Rate Procedure, reduced ventilation 
airflow rates may be calculated for each HVAC zone in the 
proposed design with a zone air distribution effectiveness 
(Ez) > 1.0 as defined by Table 6-2 in Standard 62.1. 
Baseline ventilation airflow rates in those zones shall be 
calculated using the proposed design Ventilation Rate 
Procedure calculation with the following change only. Zone 
air distribution effectiveness shall be changed to (Ez)=1.0 
in each zone having a zone air distribution effectiveness 
(Ez)>1.0. Proposed design and baseline design Ventilation 
Rate Procedure calculations, as described in Standard 62.1, 
shall be submitted to the rating authority to claim credit 
for this exception.

c. If the minimum outdoor air intake flow in the proposed 
design is provided in excess of the amount required by the 
rating authority or building official then the baseline 
building design shall be modeled to reflect the greater of 
that required by the rating authority or building official 
and will be less than the proposed design.

On 8/16/2011 8:56 AM, Anne Juran wrote:
> 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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-- 
Jason Glazer, P.E., GARD Analytics, 90.1 ECB chair
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