FW: Re: [TRNSYS-users] RE: Surface emissivity

[Fernando Domínguez Muñoz]

Dear Joseph,

I think that you can change the long wave emissivity by changing the
Stephan-Bolzmann constant

4*sigma*epsilon*dt**4

Although epsilon=1. , you can change “sigma” in PREBID (project –
properties). The problem is that this change affects to all the surfaces
(indoor and outdoor). Looking at the source code of type56, it seems
that the window calculation subroutine uses its own sigma value, so the
former modification won’t affect the windows balances. 

Another solution could be to modify the STAR resistances in the source
code of type56. I suppose that this is a more difficult way.

Kind regards

Fernando.



>Dear Joseph,
>   As far as I know there is unfortunately, no way to modify the surface 
>emissivity in Type56. You can, of course modify the longwave absorption of 
>the wall surfaces. Type56 handles radiative exchange using a star network 
>method. There is radiation exchange between each surface of a zone and the 
>zone's air node. There is no direct radiative exchange between surfaces. 
>For additional information, you can refer to section 2.1.7 of the 
>06-Multizone Building Modeling with Type56 and TRNBuild manual for 
>additional information on the long wave radiation exchange calculations 
>that Type56 performs.
>Kind regards,
>   David
>
>At 01:42 AM 8/17/2005, Phine wrote:
>>Dear users,
>>
>>I am modelling a mud brick house using type 56. I would like to model the
>>impact of putting on low-e paint indoor. How can I adjust the emissivity of
>>the wall surfaces?
>>
>>Is there any standard procedure to account for such change? How does TRNSYS
>>handles the radiative heat exchange?
>>
>>Regards,
>>
>>Joseph Cheung
>>
>>
>>
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>
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