Oversizing/Undersizing Equipment

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Well the reason I am trying to create unmet load hours is per ASHRAE 90.1.
My proposed model has slightly more than 50 unmet heating hours and to get
the difference to less than 50 ASHRAE says you should decrease the equipment
capacities on the baseline building. The space in my building that has load
problems was designed as a kitchen with a significant amount of commercial
kitchen equipment, however, the kitchen installation is being delayed and
will not be completed at this time. The equipment had been creating quite a
significant heating load, but without that the proposed equipment cannot
quite meet the load. As far as the building is concerned I don't see this
as a problem because until the kitchen is installed the room will most
likely be used as storage, if for anything at all. ASHRAE requires that the
difference be less than 50 though, and I don't see anything else I could do,
other than placing the equipment back into the kitchen as though it were
being installed at the time of the building submittal.

Perhaps I am not spending enough time trying to minimize unmet hours in the
proposed model, but I am not in charge of the design, I am just putting
everything into the model. As far as I can tell I have put in all of the
variables as accurately as I can. Not to say it's perfect, but it's pretty
good.

Michael

M. Shields's picture
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Hi Michael,

thanks for the extra info, it will help me & others to help you better with
your situation. Going back to basics---it's always better to have 0.0% in
any model--this is the goal of simulation for all model files. Although it
is the goal it is not always attainable--because of so many other variables.

If I were in your shoes...I would be spending more time on reducing the
unmet load hours in your proposed model to get closer to "the goal" of
simulation, rather than working backwards and trying to make your baseline
model 'less than adequate" and trying to produce unmet loads.

If you would like to attach your .pd2 & .inp file for your proposed model
I'm happy to take a look at it and how you can reduce the unmet load hours.
Keep in mind that just because you may be getting unmet load hours in your
proposed model doesn't not specifically imply that the proposed system
design is 'inadequate' in real life. This is an example of how energy
models and 'real life' have a disconnect. As the simulation industry grows
and simulation programs conitnue to be refined the gap of this disconnect
from simulation world to real world will grow smaller.

Based on my experience you will actually spend less (billable time) trying
to adjust your proposed model file rather than manipulating your baseline
model.

Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
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Hi Every one,

I have a project which use heat pump for a two story office building. Which
report should I use to get unmet hours, SS-E or SS-R?

Many thanks,

Jennifer

Jennifer Jin's picture
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Jennifer,

start with looking at both SS-F (for each zone in your model) and SS-R for
each system in your model. You'll need to use them both simultaneously to
start understanding what your model is OR is not doing.

Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 200

Pasha,

Thanks for your quick response. SS-E report provides the annual total fas run
hours (not a zone level), will that be sufficient for a LEED submittal?

Thanks,
Jennifer

Jennifer Jin's picture
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Hi Jennifer,

I suggest the SS-F report, not SS-E. Take a look at the attached document,
this should help you understand the reports better and what information they
contain. I use this reference document ALL the time to help me analyze and
QC check my models.

Let us know if you have more questions.
Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 200

Pages 5 and 6 of that document make for great "post on the wall"
references at work.

They double as impressive light coffee table reading for one's swank
bachelor pad, to boot =)!

~Nick

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Pasha,

Thanks a lot . I looked at the document and on page 126, it says: To calculate
the total number of hours outside the throttling rage, multiply the percentage
reported here by the" Hours Fans on" reported on SS-E", But on the same page,
under "important note: it also says: To investigate any hours outside the
throttling range, see SS-R, then SS-F and SS-O to isolate the system & zone
(SS-R), time of year (SS-F) and time of day (SS-O) the control problems occur."

So I am a little confused here.
?
Thanks,
Jennifer

Jennifer Jin's picture
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Jennifer,

To find your total unmet hours, per your original question, use SS-E in
conjunction with the "unmet hours" percentage in the BEMP report. A
discussion from the not-so-far past is copied below (scroll to the
bottom) wherein eQuest developer Scott Criswell laid down the law.

SS-R, F and O are collectively very useful for tracking down exactly
when and where your unmet hours are occurring, to help track down what
might be awry to resolve them, if you should desire/need to, as the
"important note" explains. I expect this is why Pasha is bringing SS-F
to your attention.

SS-E however is what you're working with to determine LEED unmet hours,
however. Plenty of further discussion as to why in the archives (search
for 'coincidental unmet hours'). Currently there's no perfectly clean
way to distinguish coincidental unmet heating vs. cooling hours, unless
you get lucky and have zero of either. I understand an approach when
you have both is to take your total and proportion it out based on SS-R
sums...

On a related note, an easier-to-digest view of both where the unmet
hours are occurring (identifying the zone) and the unmet cooling/heating
totals for each zone is available by clicking "Air Side HVAC" then
"Summary" tabs after a calculation. Highlight any one system in the
tree to the left or click the top of the tree to see them all with sums
at the bottom. Unmet heating/cooling hours are summed for each zone -
this happens to be a fast way to identify where a cryptically-named zone
with unmet hours exists in your model, as well.

Best of luck!

~Nick

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Nick and Pasha,

Thanks a lot for your help. Now I have better understanding of unmet hourss
and?Equest reports.

Thanks,
Jennifer

Jennifer Jin's picture
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The 90.1 definition of unmet hours is very different from the
Canadian MNECB/ecoEnergy. The SS-R report is used to determine
compliance - no zone may have more than 100 under heated hours.

For a project I am doing, the SS-E times BEPS percentage yields a
proposed and budget case that meet the requirements of 90.1 Appendix G.

But both models have more than one zone with more than 100 under
heated hours as reported in the SS-R reports. As this is not a real
building, I only have to increase the heating capacity in those few
zones. A "real" project would have to re-examine zones that are
reporting too many under heated hours to determine if the model were
accurate or if the proposed design required altering.

Chris Jones

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