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Openstudio Solar Model Indicator

asked 2016-03-29 00:12:16 -0600

Arif Hanif gravatar image

Openstudio has the option for ASHRAEClearSky versus ASHRAETau, which i am trying to use to compare to TRACE 700 but when i set the option to ASHRAEClearSky i get zero fenestration solar load. Has anyone else ran Clearsky and not Tau?

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I would help if you could post the link to the documentation of the object you're manipulating and the resulting object too (from your idf)

Julien Marrec gravatar image Julien Marrec  ( 2016-03-29 03:51:44 -0600 )edit

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answered 2016-03-29 03:56:15 -0600

updated 2016-03-29 09:30:27 -0600

I'm assuming you're talking about the SizingPeriod:DesignDay object, specifically the Solar Model Indicator.

You're seeing no fenestration load because when you switch to ASHRAEClearSky it will look for the Sky Clearness (instead of the two tau values, $\tau_b$ and $\tau_d$). You probably left this field blank, which will default to 0, meaning no solar gains.

Clearness may range from 0.0 to 1.2, where 1.0 represents a clear sky at sea level. Values greater than 1.0 may be used for high altitude locations. Traditionally, one uses 0.0 clearness for Winter Design Days.


Considering that the Sky Clearness field isn't exposed in the OpenStudio App, you could do something like this to change all your summer design days (the winter ones are usually already as Clear Sky, with clearness of 0) to Clear Sky with a value of 1.0

model.getDesignDays.each do |dd|
 if dd.dayType == 'SummerDesignDay'
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So plug in a value in the Taub and Taud location within a range of 0-1.2?

Arif Hanif gravatar image Arif Hanif  ( 2016-03-29 08:26:46 -0600 )edit

No, plug a value in the "Sky Clearness" (Taub and Taud is used when selecting ASHRAETau). Try with 1.0 for summer design day for example.

Julien Marrec gravatar image Julien Marrec  ( 2016-03-29 09:03:37 -0600 )edit

I see, the field isn't exposed in the OpenStudio App (which seems weird...)

Julien Marrec gravatar image Julien Marrec  ( 2016-03-29 09:23:18 -0600 )edit

I had the same issue. It's very confusing that you can select the model but not set the sky clearness. It seems to default to zero, because it's used for the heating load calc.

jmcneill gravatar image jmcneill  ( 2016-03-29 10:42:27 -0600 )edit

I opened an issue (feature request) on OpenStudio Github here

Julien Marrec gravatar image Julien Marrec  ( 2016-03-29 10:49:02 -0600 )edit

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Asked: 2016-03-29 00:12:16 -0600

Seen: 805 times

Last updated: Mar 29 '16