[Equest-users] eQuest - outside air heating issues

[Tomlinson, Scott]

Folks,

I went thru and entered all my ventilation air at the zone level for both design and baseline systems and they are matching up, but unfortunately this wasn't my issue.  I am still getting unreasonably high gas savings, actually I think it is my design gas use that is low, not my baseline design that is high.

I have my design model pretty much put together, so to create my baseline system I take a copy of my design building and modify this.  My design AHUs are VAV with hot water reheat, and so are my baseline AHUs, so I modify 3 of the design AHUs into the baseline AHUs that will be serving each of my 3 floors (I've tried copying new AHUs and creating new AHUs from scratch at this step as well).  I clear out the CFMs and coil capacities to allow autosizing, and I redesign ate all my zones to the proper baseline AHUs.  It is this step that is causing problems.  For some reason going from 16 smaller systems to 3 larger systems causes my gas consumption to increase by a factor of 4.

My unmet hours for both models are within reason, I'm just using a bunch less gas in the design building for some reason.  Why looking thru the output report I noticed something.  My baseline building isn't generating SS-P reports for some reason.  I'm not sure if this is an indicator of something.  Any thoughts would be appreciated.


-          Scott

From: Bishop, Bill [mailto:wbishop at pathfinder-ea.com]
Sent: Wednesday, May 26, 2010 11:36 AM
To: Nick Caton; Tomlinson, Scott; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] eQuest - outside air heating issues

Scott, Nick,

To meet the 90.1 Appendix G requirement for identical minimum outdoor air flowrates, I enter OUTSIDE-AIR-FLOW cfm for all zones in both the baseline and proposed models. To get these values, I will either calculate them based on the design drawings, or get them from the SV-A reports. I set the Minimum OA Control Method to "Fraction of Design Flow" so that the fraction of OA increases as a variable air volume system ramps down.

The idea of adjusting the OA rates between systems, while creative, does not meet my understanding of the intent of Appendix G. The proposed model should simulate the actual design as closely as possible, using as much information as is known about the design. Presumably, the mechanical designer will calculate minimum OA rates for all zones per code, or ASHRAE 62.1, or both.

To verify that OA rates are actually identical between baseline and proposed models, I create hourly report blocks for at least one system to track total system supply air flow rate and ratio of outside air to total supply air.

I recently filled out the online LEED template for credit EAp2 for a LEED 2009 project, and there was a note on one of the tables that if an ERV is used, the modeler should "verify that outside air is modeled with zero flow in both cases during unoccupied periods." To meet this, I create a minimum air schedule, set to 0% during unoccupied hours and "999" for all other hours to default to the program-calculated OA percentage.

Regards,
Bill

William Bishop, EIT, BEMP, LEED(r) AP | Pathfinder Engineers & Architects LLP
Mechanical Engineer

134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 Ext. 114
F: (585) 325-6005
wbishop at pathfinder-ea.com
www.pathfinder-ea.com
P May is National Bike Month. Bike to Work Day May 21st.
________________________________
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
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

[cid:image001.jpg at 01CAFE44.11148870]

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

[cid:image001.jpg at 01CAFE44.11148870]

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

[cid:image002.jpg at 01CAFE44.11148870]



f: 617.354.5758

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

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



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