[TRNSYS-users] Zeroing inside and outside longwave radiation of window surfaces

[Oselen Imafidon]

Thank you Christina,

Please a quick clarification. I am inputting only outdoor temperature variation which is a sinusoidal daily temperature variation and all other weather inputs are zeroed. All forms of radiative heat exchange outside and inside the building are turned off. The daily  temperature is prescribed to vary between a maximum value of 40°C and a minimum value of 0°C and the indoor temperature is set at 20°C. The result shows the mean of the convective heat flux to the outside surface from the ambient air and the convective heat flux from the inside surface to the air are zero as expected. 

However, for the heat flux through the windows, the mean is not zero. Is this because of the temperature dependent properties used for the calculation of the Uvalue of the window at each time step?

Thank you for your help.

Warm regards,
Oselen Imafidon

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Sent: November 12, 2021 6:06 AM
To: 'trnsys-users at lists.onebuilding.org'
Cc: 'Oselen Imafidon'
Subject: AW: [TRNSYS-users] Zeroing inside and outside longwave radiation of window surfaces

Dear Oselen,

you are right with your idea, if you set the longwave radiation mode to simple and set the combined heat transfer coefficient equal to the convective part, the longwave radiation is effectively zeroed. One thing to keep in mind is that this is then the case for all surfaces in the room.
If you want to consider the longwave radiation for all surfaces but the window, you can use the same method you did for the outside case. You can select longwave radiation detailed mode for the zone and set the back emissivity of the glazing + the frame to 0, too. In this case the window will behave like a longwave radiation-mirror so to speak and the longwave radiation exchange will still be calculated using view factors between the other surfaces in the zone. 



Best regards,
Christina

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Von: TRNSYS-users <trnsys-users-bounces at lists.onebuilding.org> im Auftrag von Oselen Imafidon via TRNSYS-users <trnsys-users at lists.onebuilding.org>
Gesendet: Freitag, 29. Oktober 2021 15:21
An: trnsys-users at lists.onebuilding.org <trnsys-users at lists.onebuilding.org>
Cc: Oselen Imafidon <josephoselen at yahoo.com>
Betreff: [TRNSYS-users] Zeroing inside and outside longwave radiation of window surfaces 
 
Hello,
 
To zero the inside longwave radiation of the window I used the simple model longwave radiation exchange within a zone. 
 
To zero outside longwave radiation of the window, I modified both the window frame emissivity to zero and the front emissivity of the first window glazing in the building input description file (BIU) to zero. 
 
I used hand calculation to verify the simulation results using the following equations for heat fluxes to the outside and inside surface and the results were same. . The result shows inside and outside longwave radiation of window surfaces are zeroed.
 
Is this the right way of zeroing inside and outside longwave radiation of window surfaces?
 
Thank you.
 
Regards,
Oselen I
 
Sent from Mail for Windows
 

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