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Modeling Fans for LEED

asked 2015-06-17 06:44:04 -0500

hugopft's avatar

updated 2015-07-10 13:46:14 -0500

I have been modeling a building to submit it to LEED certification and I have some issues Regarding to how to set Correctly fan parameters for the baseline model . I am aware que ASHRAE 90.1 provides a table regarding to BASELINE FAN MOTOR POWER, but I am not find the relation between them and the values ​​found in OpenStudio to configurate the fans. In OpenStudio we have as a fan input The Following items:


I would like to know which one of them I have to set, and where I can get the values ​​to set them correctly. I know, for instance, that TRACE 700 when is dealing with a BASELINE model of its own calculations. I do not need to set such parameters in there, only for the proposed model.

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@hugopft this may be a duplicate of this question. If so, I will close this one.

MatthewSteen's avatar MatthewSteen  ( 2015-06-17 07:33:23 -0500 )edit

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answered 2015-06-17 13:31:32 -0500

nfonner's avatar

updated 2015-06-19 10:27:16 -0500

I built my spreadsheet based off the calculator below. It gives a good overview of how exactly to reverse engineer that fan power. Careful when switching between units.

Credit to the Integrated Design Lab (University of Idaho)


UPDATE: Not that this is really relevant to the original question (more so at the title of the question), but for any of those looking on how to complete the calculation for compliance modeling, GBCI's Table 1.4 spreadsheet >link< to track your inputs is a great tool to deconstruct for really understanding to how to model according to Appendix G of ASHRAE 90.1. Un-hide all the mechanical fan tabs and swim through all the references.

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I really appreciate the answer. I am going throught it in the next weeks and all of this stuff will be very helpfull .

hugopft's avatar hugopft  ( 2015-06-19 07:49:31 -0500 )edit

No problem. I also found this a big change coming from eQuest and Trace 700. After you distill that IDL tool down to the essential inputs and outputs, it actually becomes a much easier task to ensure compliance IMO.

nfonner's avatar nfonner  ( 2015-06-19 10:30:39 -0500 )edit

I used the spreadsheet, @nfonner. For these inputs : 2.76 m³ / s, Fan efficiency of 0.7 , the motor efficiecy of 0.88 , an A = 0 ( Been conservative ) . Then , I am getting the delta pressure output of 1188.54 Pa . I checked the values ​​as suggested in the spredsheet , and everything is all right . But , thinking about real project, I know que about 600 Pa is a reasonable delta pressure to be considered, and I am thinking that this value for the baseline is to high. Did you guys get high values ​​like this one? Is it right?

hugopft's avatar hugopft  ( 2015-07-03 09:47:17 -0500 )edit

All other inputs remaining unchanged, the Pressure Rise will decrease with more realistic Tot Fan Effs. I'm working on a project now ranging from 42.3% - 61.4%. (Packaged Rooftops - some CV and some VAV) While 70% is really quite high in my opinion, it is only a default that I choose to keep since I am not complying with Pressure Rise and Tot Fan Eff from an energy code point of view.

...and yes. I have a few in that 1200 Pa range. (PSZ-AC Sys 3 - 90.1 with ~ 2,398 cfm (1.13 m3/s), 70% Tot Fan Eff, 87.5% Mtr Eff. & a marginal increase (0.14 bhp) due to filtration credits.)

nfonner's avatar nfonner  ( 2015-07-07 09:17:29 -0500 )edit

Hi @nfonner , just to be sure that I understood it right: this range of 42.3 % - 61.3 % is the Tot Fan Effs?

hugopft's avatar hugopft  ( 2015-07-07 10:14:32 -0500 )edit

answered 2015-06-17 12:15:17 -0500

obuchely's avatar

Hello. I am not sure but I think you have to calculate manually the fans for the baseline. After you have the power you have to do some reverse calculation to convert the kW to pressure. Power= Q x P.

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I really appreciate the answer. I am going throught it in the next weeks and all of this stuff will be very helpfull .

hugopft's avatar hugopft  ( 2015-06-19 07:49:18 -0500 )edit

answered 2017-11-03 10:33:32 -0500

fp0417's avatar

Hi thanks for sharing the link to that fanpower calculator. I have a question, It seems to work well to generate the system fan power but when it comes to the energyplus - enduse output the demand (kW) does not match the system fanpower calculated from 90.1. Is it supposed to match? I can see in the equipment outputs the fan-power matches the calculator but not in the enduse. any thoughts?

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Asked: 2015-06-17 06:44:04 -0500

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Last updated: Jun 19 '15