[Equest-users] eQuest - outside air heating issues

Li, Lan lli at sbmce.com
Wed May 26 08:49:06 PDT 2010


Nick,

 

In my humble opinion, even system 3 or 4 won't have same amount of OA as
your proposed system. For the base, each thermal zone has its own RTU;
for proposed system, each thermal zone could be a VAV box. The
ventilation equation will play differently. The proposed large VAV
system will have a larger diversity factor.  I always put the same OA
quan. at room level. 

 

Thanks!

 

Lan

 

 

________________________________

From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Wednesday, May 26, 2010 11:31 AM
To: Tomlinson, Scott; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] eQuest - outside air heating issues

 

Hey Scott,

 

To be frank, I haven't yet modeled any LEED projects that would use
systems 5+, so I have no direct experience to relate.  That said, if I
were in an omniscient USGBC reviewer's shoes, and you presented this
method of matching ventilation rates, I would check that the design OA
rates for each floor are roughly matching the proposed values and design
documents.  The practice to specify MIN-OA-RATIO's at the system level
to start, then tweaking as necessary has (for me) turned out to be the
most efficient way I've found of (1) getting the baseline quantities to
start in the right vicinity relative to the proposed, and (2) maintain
an equal distribution of the OA to each zone.  As you point out, it's on
us to not bend the rules and redistribute the OA in a way that is
advantageous...  

 

Off the top of my head, I think for baseline systems 5+, I would follow
the same basic procedure, using MIN-OA-RATIO's from the proposed to get
a starting point.  For step 5, it may be appropriate to use a zonal
method to specify/tweak the resulting ventilation rates to match, it
would depend on the project-at-hand.  On the other hand, MIN-OA-RATIO
may still be a viable option if the modeler will pay mind as you say to
treat each floor/system separately and not to simply match the gross
values for the building.

 

I have not received any USGBC commentary raising issues with this
approach - as a simple disclaimer: that's not to say it has actually
been scrutinized!

 

I'd love to hear others share their approaches if you have a "normal"
procedure... I'm sure there's a variety out there and we might all learn
something =).

 

~Nick

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: Tomlinson, Scott [mailto:stomlinson at smma.com] 
Sent: Wednesday, May 26, 2010 10:12 AM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] eQuest - outside air heating issues

 

Nick,

 

First off, thanks for the reply.

 

If I am understanding you correctly, your method is getting the total OA
of each model to match up, and you are doing this at the system level
for both the design and baseline buildings.  This differs from my
method, where I am trying to get the OA rates to match up for each zone
of the two models.

 

Your method would seem to work for a baseline system type 1, 2, 3 or 4,
where each thermal block needs to be modeled as a separate system, but
for a system 5, 6, 7 or 8 (where each floor of the baseline building
needs to be modeled with a separate HVAC system) I would think you would
have difficulty getting things to match up.  When you work on these
higher system types, and you are modifying the OA ratios of your
baseline systems, do you do it equally for all the systems?  If not, I
would think this could give you some freedom the 'game' your baseline
model in a way that USGBC would not approve of.  I'm not saying you
personally would do this, let me use my current model as an example.

 

My current building is a 3 story system 8 school.  The design building
has some AHUs (about 25% OA), some ERUs (100% OA) and some UHs (0% OA).
Now, using my method of entering the OA at the zone level in the
baseline building things are working out that I need energy recovery in
the first floor HVAC system, but not the second or third floor systems.
If I use your method of getting the total building OA rates to match
(and if I am understanding it correctly), what would stop me from taking
some of the OA from the first floor system and transferring it to the
second are third floor systems so I can get all three systems under the
requirements for energy recovery, and provide myself some artificially
inflated energy savings, while keeping my total building OA rates equal?
In my very limited feedback from USGBC it seems like they don't like
letting the modeler have such freedoms.

 

Have you ever had any issues with USGBC using your method?

 

-        Scott

 

From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Wednesday, May 26, 2010 10:04 AM
To: Tomlinson, Scott; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] eQuest - outside air heating issues

 

Scott,  

 

I want to say off the bat that you actually are asking a very good and
fundamental question:  What is a "best practice" for matching baseline
ventilation air rates to the proposed model? 

 

My general processes is:

1.      where I'll build a proposed model to match the
drawings/schedules, address anything that results in odd results/
warnings / unmet hours.

2.      Build the baseline - clear out any zone/system level OA inputs
to autosize, then 

3.      For each airside system, enter the 1.15/1.25 oversizing
parameters and a "MIN-OA-RATIO" at the system level to match the
corresponding proposed design model's system ratio

4.      Run both simulations and compare results for ventilation air to
determine if things are way off (and they have been) - I use the SV-A
reports and excel for this comparison

5.      Tweak baseline systems' OA-RATIOs as required up or down to make
the total ventilation air  sync with the proposed model's.  

 

Following this procedure, which I document for model review, the design
system OA sums between the baseline model, proposed model, and
construction documents are typically very close to each other, if not
perfectly in sync.

 

Is this a procedure others are following or is there a simpler way?

 

To the rest of your email... Different systems will use different
amounts/types of energy for the same amount of load (OA).  Your baseline
model's tripling of gas consumption isn't something  I'd immediately
discount as unreasonable, but worth reviewing to find something you may
have missed - perhaps lowering CFM's are the culprit?  In some cases,
the core "secret" to surprisingly outstanding proposed/baseline
performance is getting lucky with a terrible baseline...  the
prescriptive requirements, by their nature, can be close to or far from
"a good idea" for any given project/site.

 

~Nick

 



 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Tomlinson, Scott
Sent: Wednesday, May 26, 2010 8:35 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] eQuest - outside air heating issues

 

Hello all,

 

I have a question regarding outside air input.  For my design building I
enter my outside air at the system level, as the minimum outside air
ratio, which I get from my equipment schedules.  90.1 requires that the
outside airflow be the same.  To do this I take my summary report from
my design building and enter the values from that report into the
baseline model zones.  When I run my baseline model the outside airflow
rates from the summary report match those of my design model, and my
unmet heating hours are good in both models, but the heating gas
consumption in my baseline building triples.  The result is I am getting
great, but unrealistic, energy savings.

 

Does anyone know why this is happening?  Why would entering the OA at
the zone level cause such increased heating for the save total CFM
entered at the system level?  How are you folks typically handling your
outside ventilation air.

 

Any help would be greatly appreciated, thank you.

 

__________________________________________

Scott Tomlinson, PE, LEED-AP

Mechanical

Symmes Maini & McKee Associates, Inc.

1000 Massachusetts Avenue, Cambridge, MA 02138

t: 617.520.9438

 

 

f: 617.354.5758

stomlinson at smma.com

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

 

 

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