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Calculate Coefficient of Utilization

9 REPLIES 9
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Message 1 of 10
weingartenj
3814 Views, 9 Replies

Calculate Coefficient of Utilization

Does anyone know of common mistakes in light fixture creation that would cause the the family to not Calculate the coefficient of utilization? I have the box checked in the family. When I place the element the Calc C of U is now greyed out and no longer checked. Ideas?
9 REPLIES 9
Message 2 of 10
jason.martin
in reply to: weingartenj

My guess would be that there is no light source definition for the family
defined, but without seeing the family it is just a guess.

jason

"mothball79" wrote in message news:5913133@discussion.autodesk.com...
> Does anyone know of common mistakes in light fixture creation that would
> cause the the family to not Calculate the coefficient of utilization? I
> have the box checked in the family. When I place the element the Calc C of
> U is now greyed out and no longer checked. Ideas?
Message 3 of 10
weingartenj
in reply to: weingartenj

Jason-

Take a look... Thanks
Message 4 of 10

Are you sure it is checked for all Types of that family?

Kyle B
Revit MEP Product Manager
http://inside-the-system.typepad.com/


Kyle Bernhardt
Director
Building Design Strategy
Autodesk, Inc.

Message 5 of 10
weingartenj
in reply to: weingartenj

All types are checked for the family
Message 6 of 10
jren
in reply to: weingartenj

I was also having this problem. One thing that I tried was to change the Space "Limit Offset" to be above the fixture. For example if your fixture is at 8' and the Space Limit Offset was also at 8', it sometimes does not detect the fixture.

Just something to try if your out of ideas. Your Space parameters also has to be filled in.
Message 7 of 10
Roberth300
in reply to: jren

I am still having this exact problem with Revit MEP 2012, did anybody figure this one out?

 

Thanks,

Robert

Message 8 of 10
c.era
in reply to: Roberth300

Just a thought: If you check 'calculate the coefficient of utilization' is that trying to get that information from the ies file? That is how it automatically calculates it-but you cannot use the default light sources. If you uncheck the box you can manually input a value for the CU.

Message 9 of 10
Roberth300
in reply to: c.era

I figured out that the fixture was looking for an IES file that was no longer at path given.  I guess rather than throwing up an error, it just locks out that calculation.  Once I repathed to the correct location of the .ies file, it worked again.

 

Thanks for all the help,

Robert

Message 10 of 10
sragan
in reply to: jason.martin

Just spent an hour trying to figure out the same thing.  The "Calculate Coefficient of Utilization" looks like an instance parameter in the family editor, but once the family is loaded into the project, it can't be selected or deselected.   


That is because the "Calculate Coefficient of Utilization" can only be checked if the light source is using an IES file.   If you use one of the basic light distributions (sphere, hemisphere, or point), you cannot check that box.   

 

If you are using a basic distribution, you must directly enter the "Coefficient of Utilization" for each fixture for the illumination to be calculated.  For example, using 1.00 is no light lost.

 

It would be nice if that was in the documentation somewhere, but I haven't found it.


Other things to check for no calculated "Average Estimated Illumination";

 1.  Make sure the light source is enabled in the family, and its below the ceiling and the fixture geometry.  (This would be above the extrusion in the family editor since the top of the extrusion is the bottom of the ceiling.  So light fixtures should be modeled facing up).

2.  You can also enable the "Room Calculation Point" in a fixture family.   This will make sure Revit includes the light output from fixtures located just above the ceiling.  You enable this in the "Family Category and Parameters" its just a few lines down from where you turn on the light source.   Then you can drag the point to below the fixture.

 

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