Incident Solar with a translucent awning

asked 2024-02-27 12:25:36 -0600

updated 2024-02-29 03:27:54 -0600

Hello, I tried to simulate a building on DesignBuilder with a awning opaque, with the same awning but partially translucent and without awning. The results i get don't make sense. I get that the incident solar on the wall is worse with the translucent awning then without any awning, but it is physicaly impossible. You can find my DB files and the IDF results files here: https://www.swisstransfer.com/d/356fe... If anyone has information on how to make it work or how E+ does his calcul, i take it :) Or if you need anymore information on my case don't hesitate to contact me! Thank you very much

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Bonjour Margot. It would be helpful if you shared the 2 (or 3) IDF files:

no awning
translucent awning
opaque awning (optional)

Denis Bourgeois ( 2024-02-28 08:53:56 -0600 )edit

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answered 2024-02-29 16:24:58 -0600

Denis Bourgeois
2981 ●111 ●8 http://www.rd2.ca

(not a definitive answer - just poking around)

I don't have DesignBuilder, but ran both IDFs (noA == "no awning", vs A == "awning") with E+ 9.5, for a similar climate. August results for Zone 1, Wall 4 Window:

Surface Outside Face Incident Solar Radiation Rate per Area: noA (135 W/m2) vs A (120 W/m2)
Surface Window Transmitted Solar Radiation Rate: noA (165 W) vs A (114 W)
Surface Window Heat Gain Rate: noA (115 W) vs A (123 W)

Incident and transmitted rates are what one would expect. Yet the overall window heat gain rate is indeed greater with the awning (+7%). If the awning is left permanently deployed in August, then this increase could be explained by a lack of radiative cooling at night; a permanent awning would in part hinder the window from seeing the night sky. A detailed hourly comparison of diurnal vs nocturnal window heat gain/loss rates (or dynamically retracting the awning at sunset) may reveal this ... but I'm out of time :[.

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Hello Denis, Thank you very much for your reply and explanation. It makes much more sense now. Do you know why do we get this result on the window, but not on the entire wall?

margot@assemblage.net ( 2024-03-04 04:13:22 -0600 )edit

Hi Margot. Something to consider: the "Heat Gain Rate" outputs are tallied "when the total heat flow is positive" (i.e. from outdoors to indoors). This will happen more frequently for an exposed window than a exposed wall. Can't really say without taking a deeper dive. For a wall, this means looking into material composition (U, thermal inertial response), % of the wall shaded over the course of a summer day, etc.

Denis Bourgeois ( 2024-03-04 06:55:33 -0600 )edit

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Incident Solar with a translucent awning

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Incident Solar with a translucent awning