[Bldg-sim] Exceptions to G3.1.1, and how you model them?

[Julia Beabout]

I've always interpreted the exceptions you mention as an alternative way in 
which special spaces MAY be modeled but don't HAVE to be modeled. 

My experience has been mostly with labs and hospitals which have pressurization 
requirements and thus typically meet one or more of the criteria for the 
exception to be used. 

LEED reviewers and CIRs have generally upheld the optional approach and allowed 
all the pressurized spaces to be put on the main systems since using individual 
separate units to model hospital rooms or labs is not in line with what could be 
done in reality.  

It may be helpful for you to take a look at the CIRs on the subject as related 
to application to labs and hospitals.  These could be rather enlightening 
regarding the "spirit" and application of the exception.  





________________________________
From: Carol Gardner <cmg750 at gmail.com>
To: James Hansen <JHANSEN at ghtltd.com>
Cc: bldg-sim at lists.onebuilding.org
Sent: Sun, November 7, 2010 11:31:46 PM
Subject: Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them?

Hi James,

I must chime in on this. First off, in reality I would more expect to see a 
transfer grille above the door of the storage room, bathroom, etc., than I would 
expect each to have their own system. I frequently model them as unconditioned 
spaces attached to a HVAC system and call it good. Mostly if a room of that type 
is conditioned, it is fed off the nearest system. Stairs may be separately 
heated with a unit heater, which I would model in the proposed case, but for the 
baseline I'd just stick to what makes "engineering" sense following the spirit 
of the code.

Best,

Carol


On Mon, Nov 1, 2010 at 1:43 PM, James Hansen <JHANSEN at ghtltd.com> wrote:

I see, that makes a little more sense.  So if I had a stairwell, which does not 
have HIGHER process loads than the average space, and whose occupancy schedule 
is basically the same as the rest of the office space, then I would HAVE to have 
that stairwell on the base-building System 5-8.   I couldn’t have it on its own 
PSZ-AC. 

> 
>Mike, this goes against what you said in your email.  This is sort of why I 
>asked the question…there doesn’t seem to be a consensus.  I model stairwells, 
>elevator shafts, bathrooms, etc as separate thermal zones in all of my models, 
>and if I read the letter of the code, it would seem they need to be their own 
>systems, yet the CIR sort of says that this isn’t the case, and reviewers agree, 
>and don’t like to see rooms like this on separate systems.
> 
>From:Cheney [mailto:chenyu73 at gmail.com] 
>Sent: Monday, November 01, 2010 4:35 PM
>
>To: James Hansen
>Cc: bldg-sim at lists.onebuilding.org
>Subject: Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them? 
> 
>Hi James, 
> 
> 
>The CIR is dated on 3/23/2007. It clarifies use of exception to G.3.1.1. to 
>document baseline and achieve greater energy savings from single-zone systems in 
>high process load areas. 
>
> 
>As per G3.1.1. in Appendix G (90.1-2004), my understanding is to use separate 
>single-zone system for any space has very high occupancy or process loads or 
>schedules that differ significantly from the rest of the building. You can 
>understand it in the opposite way that the rooms have significantly less 
>occupancy or process loads. But I guess the CIR points to the high process load 
>areas in order to achieve greater energy savings from single-zone systems. 
>
> 
>Regards, 
>Cheney 
>On Mon, Nov 1, 2010 at 12:46 PM, James Hansen <JHANSEN at ghtltd.com> wrote:
>Thanks Cheney, but I’m not sure I follow your email.  I’ve already determined 
>that, for example, a core bathroom could easily have a peak load that is 10 
>Btu/hr-ft2 less than the peak average of the rest of my spaces.  Same goes for 
>stairs, storage rooms, etc.  So doesn’t 90.1 REQUIRE that I model these 
>separately?
> 
>What CIR are you referencing?
> 
>From:Cheney [mailto:chenyu73 at gmail.com] 
>Sent: Monday, November 01, 2010 12:36 PM
>To: James Hansen
>Cc: bldg-sim at lists.onebuilding.org
>Subject: Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them?
> 
>Hi James, 
> 
>LEED CIR allows projects to demonstrate substantial energy savings for 
>well-designed HVAC system serving high process load spaces based on the 
>exception to G3.1.1. So the premise is "high occupancy or process load" spaces, 
>such as server rooms, natatoriums, before it comes to the benchmark of 10 
>btu/h-ft2. Therefore, I guess your storage rooms, stairs, mechanical rooms 
>should not be modeled separately. 
>
> 
>Regards, 
> 
>Cheney 
> 
>I guess your storage rooms, stairs, mechanical rooms, lobbies, etc. should not 
>be  
>On Mon, Nov 1, 2010 at 5:12 AM, James Hansen <JHANSEN at ghtltd.com> wrote:
>I was interested to see if anyone would share how they model the exception to 
>G3.1.1 in ASHRAE 90.1-2007 (or 04).  This is the part that says when you have a 
>baseline building with system 5-8, you’re supposed to model system 3 or 4 for 
>any spaces that “have occupancy or process loads or schedules that differ 
>significantly from the rest of the building.”  It goes on to say that basically 
>the peak thermal loads must differ by 10 Btu / h-ft2 or more from the average of 
>the other spaces, or that schedules must differ by more than 40 full load hours 
>per week, for this exception to apply.
> 
>I’ve had reviewers question certain rooms that I’ve put on separate PSZ-AC 
>systems, and so I’ve sort of defaulted to putting almost all rooms on the main 
>systems (5-8).   However, in looking at some of my recent models, depending on 
>interior loads and climate, the actual peak cooling load on a square foot basis 
>varies anywhere from 5-20 btu / h-ft2 range for offices.  So this means there is 
>a big difference between those models with 5 btu / h-ft2 peak and those with 
>20.  For the models with 5, almost every space in the building is going to be 
>within +/- 10 btu/h-ft2 of that average.  However, those buildings that average 
>around 20 will have many rooms that are < 10 btu/h-ft2 peak (ie any internal 
>space whose light + plug load density is < 3.0 W / sq ft).
> 
>To use a simple example as a question:  if your particular office building 
>averaged 20 btuh / h-ft2 peak cooling load, would you model a separate PSZ-AC 
>system for a core bathroom, whose peak cooling load is only 3 btu/h-ft2?
> 
>There are lots of rooms where I question whether I should do a separate 
>PSZ-AC/HP system (storage rooms, stairs, mechanical rooms, lobbies, etc).  I can 
>see where these meet the 10 Btu/h-ft2 delta exception.  
>
> 
>So does everyone really model a bunch of PSZ-AC systems based specifically on 
>the average peak thermal loads of the building?
> 
>I’m thinking out loud, but if I had an office building that averaged on the low 
>side (5 Btu/h-ft2) for cooling peaks, it seems pretty easy to have a perimeter 
>conference room that exceeded 15 Btu / h-ft2 peak.  Seems like an exhaustive 
>process to confirm this delta for every room in a model to determine whether it 
>needs its own system…
> 
>Sorry for the long email.  Thanks!
> 
>GHT Limited
>James Hansen, PE, LEED AP
>Senior Associate
>1010 N. Glebe Rd, Suite 200
>Arlington, VA  22201-4749
>703-338-5754 (Cell)
>703-243-1200 (Office)
>703-276-1376 (Fax)
>www.ghtltd.com
> 
> 
>
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 The information contained in this communication is confidential, may be 
privileged, and is intended only for the use of the addressee.  It is the 
property of GHT Limited.  Unauthorized use, disclosure or copying of this 
communication or any part thereof is strictly prohibited and may be unlawful.  
If you have received this communication in error, please notify me immediately 
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-- 
Carol Gardner PE
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