[Bldg-sim] Modelling diversity in single zone apartments

Duggin, Cory Cory.Duggin at tlc-eng.com
Wed Dec 4 06:57:59 PST 2013


I would think as long as you have properly accounted for the diversity via the schedules, the systems should just not run as long because there is less heat to remove from the space.  The only effects you are not capturing is if only one of the apartment zones should be perimeter, but you are grouping both into a single zone that sees the combined load.  That could change how often the core zone would come on versus the perimeter.  At any rate, I think the cycling of the unit on less often should get  you close to showing the diversity effects.

Cory Duggin, EI
Energy Engineer I
direct: 615-346-1939



From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Patrick Bivona
Sent: Wednesday, December 04, 2013 8:48 AM
To: Michael Tillou
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Modelling diversity in single zone apartments

Hi Mike,

I agree that splitting 160 apartments in 2 is work that I'd rather avoid if I can! I was originally considering adjusting schedules to represent diversity. That works ok for internal gains. I have trouble seeing how that can work for cooling equipment in a single zone apartment; it's either on or off. Having one zone with diversified internal gains and cooling on is not the same thing, in terms of energy use, as having 2 zones, one of which has cooling turned off. But maybe that's ok as long as both proposed and baseline are the same?

Thanks,
Patrick


On 3 December 2013 23:34, Michael Tillou <michael.tillou at gmail.com<mailto:michael.tillou at gmail.com>> wrote:
Great conversation.

One thing I didn't see mentioned in the discussion is the fact you can diversify the internal loads within the apartment (and office spaces) to better reflect the engineers "experience" of load diversity.  This will have a direct effect of reducing peak cooling and would save you having to split up your apartments into separate zones.

In my experience, more zones does not always equal better results but it always equals more headaches and a lot more work.

To setup your operating schedules to account for diversity whether it's within a single zone or across an entire building use a weighted average approach.   For example, if the connected lighting load in the apartment is 1W/sq.ft. and the living area and the apartments have equal areas and the lights in each area are never on at the same time then lighting power would never be more than 0.5W/sq.ft. You would use a maximum value of 0.5 in your lighting schedule to describe this case.

As Nick pointed out previously your diversified schedules would need to be the same in both the baseline and proposed models.

Another thing that might help is to try and duplicate the engineers peak cooling load calc within the model.  I'm not sure what software you're using but several tools allow you to do a "peak load calculation" for equipment sizing that is separate from the actual 8760 simulation.  If your tool has this capability you could setup a design cooling load calculation similar to what the engineer will do (e.g. using ASHRAE 1% CDT and all internal loads and occupancy at 100% for the entire day).  With that calculation you can examine the theoretical building peak cooling load and then compare that to the actual building cooling load under a diversified operating schedule.  You can then determine whether the 50% diversity is a valid assumption for this project.

Mike


Michael Tillou, PE, BEMP, LEED AP BD+C
Atelier Ten

T +1 (212) 254 4500 x208





From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Patrick Bivona
Sent: Tuesday, December 03, 2013 10:18 AM
To: Nick Caton; David Eldridge
Cc: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>; Aaron Smith

Subject: Re: [Bldg-sim] Modelling diversity in single zone apartments

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<mailto: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.



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<http://www.smithboucher.com>

From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto: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<mailto: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<mailto: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<mailto: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<tel:616%20450%208653>

From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto: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<mailto: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<mailto: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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