[Bldg-sim] Modelling diversity in single zone apartments

Michael Tillou michael.tillou at gmail.com
Tue Dec 3 08:34:42 PST 2013


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] 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; 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> 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

 <http://www.smithboucher.com> www.smithboucher.com 

 

From:  <mailto:bldg-sim-bounces at lists.onebuilding.org>
bldg-sim-bounces at lists.onebuilding.org [mailto:
<mailto:bldg-sim-bounces at lists.onebuilding.org>
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:  <mailto:bldg-sim at lists.onebuilding.org> 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
 <http://www.buildingperformanceteam.com/> www.buildingperformanceteam.com 
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
 <tel:616%20450%208653> 616 450 8653

 

From:  <mailto:bldg-sim-bounces at lists.onebuilding.org>
bldg-sim-bounces at lists.onebuilding.org [mailto:
<mailto:bldg-sim-bounces at lists.onebuilding.org>
bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Aaron Smith
Sent: Friday, November 29, 2013 6:49 PM
To: Patrick Bivona;  <mailto:bldg-sim at lists.onebuilding.org>
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:  <mailto:bldg-sim at lists.onebuilding.org> 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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