[Equest-users] eQuest - outside air heating issues

[Tomlinson, Scott]

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

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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

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f: 617.354.5758

stomlinson at smma.com<mailto:STomlinson at smma.com>

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



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