[Equest-users] Oversizing/Undersizing Equipment

[Pasha Korber-Gonzalez]

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

On Mon, Aug 2, 2010 at 7:14 AM, M. Shields <mshields at fstrategies.com> wrote:

>  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
>
>
>
> *From:* Pasha Korber-Gonzalez [mailto:pasha.pkconsulting at gmail.com]
> *Sent:* Friday, July 30, 2010 3:47 PM
> *To:* M. Shields
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Oversizing/Undersizing Equipment
>
>
>
> Michael,
>
>
>
> It depends.   which is always the answer with whole building simulation
> questions.  From my experiences very rarely; (i repeat) very rarely do I
> experience unmet loads due to under-sizing of equipment.  It has only
> happened to me if I am the one trying to size equipment (where I am not a
> designer-I am the energy modeler.)   My point being; typically my unmet
> loads issues are stirred up by some input or control toggle that I did, or
> didn't do within my model inputs.  Sometimes if I encounter under-heating
> hours it is due to my zoning pattern and the skin losses (in heating
> dominated climates) are significant that my perimeter depth zoning isn't as
> accurate as it could be.
>
>
>
> Where the daily goal of us simulators is to create models that don't
> have unmet load hours, or as very little as possible it is entertaining that
> you are trying to work backwords abit.  lol.   But I recognize the
> analytical trait and good-job for seeking an answer.   I can only give you
> what my experiences have been, and there is so much to learn and understand
> about the unmet-hours phenomena keep looking for more answers and
> explanations.
>
>
>
> In terms of your project, you might not be experiencing unmet load hours
> because of how you have specified your inputs in your model (regardless if
> they are linked to sizing-ratios).   What is the climate of your project?
> What is the building occupancy type? What type of extreme loads are you
> seeinhis g on your building directly or indirectly?  Did you input your
> equipment capacities or are you auto-sizing?, Etc., etc.   It depends.  tell
> us more about your project.
>
>
>
> Pasha
>
> On Thu, Jul 29, 2010 at 3:23 PM, M. Shields <mshields at fstrategies.com>
> wrote:
>
> Hi Everyone,
>
>
>
> I have been messing with the equipment sizing ratio in equest and came
> across an interesting litte dilemma.  I was playing with the “Heat sizing
> Ratio” on the System Heating->Coil Cap/Control tab to see how it affects my
> unmet hours.  As I decrease the ratio here I see in the reports that the
> system size does in fact decrease, yet no matter how low I make the ratio, I
> never have unmet hours.  This appears to be because the supplemental heat
> increases as the equipment size decreases.  Is there a way to limit
> supplemental heating as well, or how would I be able to make my system have
> unmet hours?  I am using a heat pump system.
>
>
>
> Thanks,
>
> Michael Shields
>
>
>
>
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