[Equest-users] Oversizing/Undersizing Equipment

[M. Shields]

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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