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Openstudio Air-Cooled Chiller Default Curve

asked 2016-09-12 16:31:25 -0500

robianson gravatar image

updated 2017-09-09 13:33:32 -0500

This seems related to this post: but I think it's different enough to warrant its own question. The gist is that it seems that the default air-cooled chiller EIR-fPLR chiller curve doesn't seem to be representative of most chillers, or any reasonable default.

The EIR-fPLR curve assigned to an air-cooled chiller when you pull it out of the library has the following coefficients:

a 1.6853121,

b -0.9993443,

c 0.3140322,

This curve looks nothing like any of the curves in the EnergyPlus Air-Cooled chiller library or any of the Comnet or DOE-2 default curves. According to this curve, chiller energy usage will actually increase as PLR decreases, which is obviously incorrect. Seems like there must be a reference off somewhere? The CAPFT and EIRFT default curves look very similar to those of the other curves I can find. I'm using OS version 1.12.0, but looking at an old version of the library from 1.11.0, I think the default EIRfPLR curve is the same. Is this a mistake in the library?

I'm attaching chart graph comparing the EIRfPLR curve evaluated compared to the DOE-2 and Comnet default curves that Julien Marrec posted in the question linked above. As you can see, they're pretty drastically different!C:\fakepath\OS Default EIRfPLR Air-Cooled Chiller Curve Comparison.PNG

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answered 2016-09-15 12:26:20 -0500

updated 2016-09-15 12:36:09 -0500

I don't suggest using the current (1.12.4) OpenStudio default air-cooled chiller curves. Instead, I recommend using @Kyle Benne's measure from this answer and using a chiller from resources > chiller_library.idf that is close to the chiller you're modeling.

Alternatively if you have performance data you can use the CurveFitTool.xlsm that comes with EnergyPlus (~\PreProcess\HVACCurveFitTool\ folder) to generate custom curves.

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Thanks a lot, Matt! Both of those things are good to know about. It isn't that difficult to put in your curves manually, but it is nice to have a measure to do it.

robianson gravatar image robianson  ( 2016-09-15 15:05:54 -0500 )edit

answered 2016-09-15 10:34:17 -0500

This is actually probably just a mistake. The curves were originally copied from some version of the DOE Prototype Buildings years ago. For what it's worth, the OpenStudio default HVAC curves have not been reviewed or vetted. If the quality of these default curves is important to you, please add it to the feeback site so that we can prioritize accordingly.

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Thanks a lot for the response, Andrew! I'll add it to the feedback page. I think you're right that it's a mistake. It's not that the specific curve is particularly important, but it is important that if there's an object built into OpenStudio called "air-cooled chiller," by default it behaves at least somewhat like a generic air-cooled chiller.

robianson gravatar image robianson  ( 2016-09-15 14:49:27 -0500 )edit

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Asked: 2016-09-12 16:31:25 -0500

Seen: 1,407 times

Last updated: Sep 15 '16