[Bldg-sim] Modelling diversity in single zone apartments

David Eldridge DEldridge at grummanbutkus.com
Mon Dec 2 18:46:29 PST 2013


I don't think the issue is the separate rooms. The diversities used by the designer are most likely:


1.       Different profiles  for the E/S/W orientations due to solar load occurring at different times of day - should calculate within energy model

2.       Each FCU is oversized compared to the peak load due to safety factors and rounding up to next size available from the factory - modeled loads should be slightly lower than the entered capacities

3.       Apartments won't be occupied and/or using their appliances all at the same time - this is the tricky one that is up to you to enter in some form

4.       0.5 doesn't seem like a calculated diversity - they may be using prior projects as a guide

However if the thermostats don't have integral occpuancy controls, I wouldn't make an assumption that the residents have turned off any particular thermostat at any time, and you'll have to decide for yourself if that means changing the model to increase the quantity of zones.

You could approximate the intensity of apartment loads by having some on and some off in groups, or all of them on the same schedule using an average amount of internal gain from lights and appliances. If you are having trouble matching the plant capacity of the designers with the model, you should confirm their BOD in terms of calculating the diversity, and what quantity of internal gains they assumed, etc.

Lastly take a look at square feet per ton as a benchmark to see where the plant is coming in. Does it compare with other projects in that area?

David



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates



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<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




_______________________________________________
Bldg-sim mailing list
http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
To unsubscribe from this mailing list send  a blank message to BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20131203/77406729/attachment-0002.htm>


More information about the Bldg-sim mailing list