OpenStudio Hard-Sizing vs. Auto-Sizing

asked 2018-04-08 11:16:11 -0500

Matt Koch's avatar

updated 2020-01-22 05:53:27 -0500

I know there has been some discussion on this, e.g. here, but I do not believe it helps answer my specific concern.

There are situations in which one must enter the building exactly as designed, without any auto-sizing whatsoever, and then just let it simulate to see what the energy consumption, AHU OA fraction and unmet hours are, for example. Is that currently possible, just from OpenStudio? Would the OpenStudio simulation control tab settings work outright for this, or must one still use the "disable/enable sizing" EnergyPlus measure for OpenStudio that is pointed to within the above link?

Also, there are situations in which most of the building must be entered exactly as designed (hard-sized), but where there are parts that are not fully designed yet (e.g. core and shell). For these, the latter must still be auto-sized, but not the rest. For example, I have given all chillers (BTU/h), pumps (gpm), AHU fans (cfm) and most VAV (cfm) hard-sized (as-designed) capacities. Other parameters on these are still auto-sized, because I do not know or care about them, and there also some VAV auto-sized where I do not know their cfm (not designed yet).

Here, the OpenStudio simulation control tab settings or the "disable/enable sizing" EnergyPlus measure for OpenStudio do not seem to make any difference, which I suppose is because some auto-sizing is still required and OpenStudio recognizes that and thus just implements it anyway? At least that is what I infer form the above link?

What I would expect to happen, though, is that the OpenStudio sizing fills in the missing parameters but does not affect the hard-sized parameters, and then runs the simulation resulting from that, basically seeing how well the hard-sized (as-designed) components can handle the building, and knowing that the auto-sized components can handle their part of the building anyway.

Where I get thrown off is the zone sizing. Why does that still have to happen when e.g. the "VAV with Reheat" driving a zone has been hard-sized (cfm)? Or is that because there are other parameters of the "VAV with Reheat" that I left on auto-sized, so it must do the sizing anyway to get to these? And, as it does that, does it then overrule the original hard-sized (cfm), or does it use the hard-sized and auto-sized parameters in a complementary fashion?

Given that it is probably impossible to find as-designed answers for the hundreds of parameters that need to be filled in, I think defaulting to auto-sizing is probably the safe way to go for OpenStudio (as was pointed out in the above link), just don't create the illusion that the simulation control tab has any meaning then, I suppose, or be more clear about it? And, please do confirm that anything hard-sized is not being touched at all when sizing is (defaulted to) on.

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@Matt Koch does this post answer your question?

Aaron Boranian's avatar Aaron Boranian  ( 2020-06-02 17:13:05 -0500 )edit