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
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
seeing 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