[TRNSYS-users] Convective heat transfer coefficients of a "large opening" between zones

[David Bradley]

Knut Erik
I would imagine that your adjacent window is a virtual window, there 
only to provide you with the ability to set a shading factor when the 
screen is pulled across. If that is the case, I would leave the 
convective coefficients for the window alone whether the screen is 
pulled or not. I would, however, define a coupling air flow through the 
window and set its value differently when the screen is open and when it 
is closed. Make sure that you transfer approximately the same amount of 
air in both directions (up and down through the virtual window) Knowing 
what value to pick for the coupling air flow is difficult. Ideally you 
would use one of the airflow models coupled with the Type56 building in 
order to assess it (COMIS, CONTAM, or TRNFLOW). However, this isn't an 
ideal solution either because those bulk air flow models base their flow 
on temperature and pressure differences. In the case of a large 
horizontal opening, this means that flow can only go one direction at a 
time, which has a tendency to over pressurize either the zone above or 
the zone below and cause convergence problems. The most correct solution 
is to do some CFD work and learn what the net transfer of air through 
the opening is. If that is outside the scope of what you are doing, I 
would pick a fairly high air change rate (5ach/h?) and apply that as the 
coupling flow when the screen is open.
Best,
 David


knut.erik.enerstvedt at niva.no wrote:
>
> Hello,
>
> I have an ADJACENT window (with shading) between two Type 56 zones to 
> model a controlled screen which can be either pulled across or pulled 
> away. Does anybody know what the convective heat transfer coefficients 
> of the window should be when the screen is pulled away (that is, when 
> the window is "gone" and there is just a large opening between the 
> zones)?
>
> All help is higly appreciated.
>
> Regards,
> Knut Erik Enerstvedt
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