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

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@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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