[Bldg-sim] Modelling diversity in single zone apartments

[Patrick Bivona]

Nick, David,

Thanks for your feedback. I can see there's room for sophistication when
wanting to calculate a proper diversity factor! After discussion with the
designers, they confirmed they considered that occupants would not be
cooling all the rooms at once and that 0.5 was not a calculated diversity
but from experience. And thermostats are under the occupants' control.

I would have been a bit more conservative but hopefully the peak load in
apartments will come (shortly) after people leave the office part. I guess
I'll be able to confirm all that once I make progress on the model and see
how much slack the chillers have around that time.

Regards,
Patrick




On 2 December 2013 23:57, Nick Caton <ncaton at smithboucher.com> wrote:

>  Hi Patrick,
>
>
>
> Another substantial source of diversity to consider, for a large building
> and assuming a decent thermal envelope, is that in your most extreme
> after-occupancy/regular operation* cooling case it’s likely not every zonal
> unit in the building would operate simultaneously.  Consider that for a
> simple square building, no more than 2 wall facades should be getting hit
> with direct sunlight at any given hour – so in turn the perimeter zones on
> the other two orientations would have a fraction of their design cooling
> loads for those hours.
>
>
>
> I would NOT level any judgements, but 100% agree you should be
> collaboratively discussing with the mechanical designers understand how
> they came to that degree of capacity diversity so that your model matches
> what they are expecting to see.  You may want to prepare a summary of the
> current model’s behavior/expectations regarding chiller capacity (via an
> autosizing run) to help marry your sets of assumptions with respect to
> building occupancy/operation.  As far as LEED rigor is concerned, when it
> comes to assumptions of design and building operation (whether in the
> construction documents or not), it’s relatively defensible to put forward
> that you’re matching what the engineer of record has determined for the
> project (whether you’re discussing setbacks, setpoints, or anything
> similar).   Be mindful many such inputs need to be applied to both baseline
> and proposed models uniformly.
>
>
>
> 2 systems per apartment sounds correct from the description, and I also
> agree from some recent experience with a mixed-use building that you’ll
> likely want to have a separate set of occupancy and system operations
> schedules defined for the residential vs. nonresidential spaces, for
> reasons already discussed.
>
>
>
>
>
> Best regards,
>
>
>
> ~Nick
>
>
>
> *Note from an electrical perspective, it is more typically prudent to
> design capacity for such cases of 100% operation, as every system may in
> fact need to run simultaneously, particularly after a power outage, when
> the building is first coming online.  Sometimes BMS programming is set up
> to limit and/or stage system operation in consideration of electrical
> service size limitations, however.
>
>
>
> [image: cid:489575314 at 22072009-0ABB]
>
>
>
> *NICK CATON, P.E.*
>
> SENIOR ENGINEER
>
>
>
> Smith & Boucher Engineers
>
> 25501 west valley parkway, suite 200
>
> olathe, ks 66061
>
> direct 913.344.0036
>
> fax 913.345.0617
>
> www.smithboucher.com
>
>
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Patrick Bivona
> *Sent:* Monday, December 02, 2013 10:06 AM
> *To:* Dru Crawley; David Eldridge; Aaron Smith; Jim Dirkes
> *Cc:* bldg-sim at lists.onebuilding.org
>
> *Subject:* Re: [Bldg-sim] Modelling diversity in single zone apartments
>
>
>
> Hi,
>
>
>
> Thank you all for your answers. I may have confused everyone. The design
> team used a diversity of 0.5 for the cooling equipment in the apartments
> only. They haven't assumed this for the whole building.
>
>
>
> Still, knowing that these are high-end apartments, I'm not entirely
> convinced that people will turn cooling off when they don't occupy a space.
> But if that's the assumption, I should go with it, right?
>
>
>
> I had a look at the high-rise office/apartment model Dru pointed me to.
> It's interesting to note that the apartments are modelled as single-zone
> with cooling running 100% time and no setback.
>
>
>
> So in conclusion, if I want to stick to the assumption of the design team,
> I should split the apartment in 2 zones so that the FCUs in bedrooms and
> living rooms can have different operation schedules.
>
>
>
> Cheers,
>
> Patrick
>
>
>
>
>
> On 2 December 2013 06:49, Dru Crawley <dbcrawley at gmail.com> wrote:
>
> You may also want to look at the multifamily building models that PNNL
> uses for evaluating 90.1 changes:
>
>
>
> http://www.energycodes.gov/development/commercial/90.1_models
>
>
>
> (towards the bottom of the table). The 'Scorecard' XLS shows all the
> inputs and where there were derived.
>
>
>
>
>
>
>
> On Sun, Dec 1, 2013 at 6:22 PM, Jim Dirkes <
> jim at buildingperformanceteam.com> wrote:
>
>   Patrick,
>
> Here are a few considerations:
>
> 1.       Apartments for working people will have low loads during the day
> and high loads at night.  The offices will have the reverse pattern.
> Depending on the actual office schedules, the actual residential occupancy
> pattern and the ratio of office / residential space, 50% might work very
> well.  50% may also be rather close to “irresponsible” unless the local
> population is very tolerant of room temperatures that are a few degrees
> higher than normal!
>
> 2.       Regardless of #1 above, a LEED project should model the building
> based on the architect and Engineer’s “Basis of Design” (BOD) document.
> The scheduling and diversity patterns I mention in #1 are not commonly part
> of a BOD document, but in your case they sound critical.  You should
> (strongly) request this information!  If you make assumptions that differ
> from the Engineer’s you may spend endless hours trying to reduce unmet
> cooling load hours (and probably will not get paid for them)
>
> 3.       Once you are confident of the schedules that have been assumed
> by the BOD, you should be able to represent them for the energy model.
>
>
>
> Note: Because each apartment has two fan coils, each with a thermostat,
> you really have two zones.  This may become important for the cooling
> diversity.
>
>
>
> *James V Dirkes II, PE, BEMP, LEED AP*
> *www.buildingperformanceteam.com*<http://www.buildingperformanceteam.com/>
> *Energy Analysis, Commissioning & Training Services*
> 1631 Acacia Drive, Grand Rapids, MI 49504 USA
> 616 450 8653
>
>
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Aaron Smith
> *Sent:* Friday, November 29, 2013 6:49 PM
> *To:* Patrick Bivona; bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Modelling diversity in single zone apartments
>
>
>
> Patrick,
>
>
>
> I suspect they didn't assume that the bedroom wasn't cooled at the same
> time as the living room. They may have assumed that the cooling schedule of
> the office space is different than the apartments - maybe 8am to 5pm M-F
>  for the offices and close to the opposite for the apartments. Or they may
> have determined that the building peak load was 50% of the sum of the
> individual loads. A more likely scenario would be that the combined affect
> of both of those might equal 50%.
>
>
>
> I don't think it would be acceptable to turn cooling off in half of the
> apartments even if you did the same thing in the Baseline building. Are you
> running into issues with the chiller being undersized?
>
>
>
> Aaron
>
>
>
>
>
> *From: *Patrick Bivona
>
> *Sent: *Thursday, November 28, 2013 23:32
>
> *To: *bldg-sim at lists.onebuilding.org
>
> *Subject: *[Bldg-sim] Modelling diversity in single zone apartments
>
>
>
> Hi all,
>
>
>
> I'm modelling a mixed office/residential tower building with 160
> apartments in tropical climate, for LEED. The apartments are centrally
> cooled with fan coil units, in the living room and bedrooms. The design
> team sized the chiller with a diversity of 0.5, probably assuming that when
> the occupants are in the living room, they're not cooling the bedrooms or
> something of the sort.
>
>
>
> Given the number of apartments, I modelled each apartment as a single
> block. I cannot use zone multipliers because of the specific geometry of
> the building. I have one combined FCU for each apartment, which is of
> course either on or off. I'm also grouping apartments based on orientation,
> but that's beside the point.
>
>
>
> My question is about an approach to modelling the diversity of use of FCUs
> in the apartments. With my modelling simplification, I cannot model the
> diversity of cooling within an apartment. So what would be an acceptable
> approach?
>
>
>
> I can only think of turning cooling off in half of the apartments, though
> apartments with cooling turned off are occupied and have internal loads.
> Would a LEED reviewer be ok with such an approach. Or is there a better way?
>
>
>
> Thanks,
>
> Patrick
>
>
>
>
>
>
>
>
>
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