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

[Carol Gardner]

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
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> 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
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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 by return e-mail or by e-mail to ght at ghtltd.com, and
> destroy this communication and all copies thereof, including all
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-- 
Carol Gardner PE
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