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[TRNSYS-users] Modelling a greenhouse thermal screen by using an internal window in Type 56




Hello TRNSYS users,

I am modelling a horizontal thermal screen in a greenhouse by using an internal (ADJACENT) window between to zones in Type 56, one below and one above the window (screen). The "window" is a virtual window with no glazing and no frame to let all the radiation through to the lower zone when the screen is open. I have defined an internal shading factor controlled by an input variable to model the effects when the screen is opened or closed. In the Window Type Manager, I wonder about the following settings:

Optional Properties of Shading Devices:

Additional Thermal resistance: Can I use this to set the thermal properties of the screen? Will it be effective only when the shading factor is greater than zero?
 Reflection Coefficient of Internal Device: How should I set this?

Convective Heat Transfer Coefficient of Window: Should I use 0 (direct contact) when the screen is open and 11 (inside value) when it is fully closed?

 I also have a question about coupling of air flow between the upper and lower zones. I use an equation based on the degree of screen opening, temperature difference and density difference to calculate air flowrate across the screen. The direction of flow depends on the level of temperature and/or density in the two zones. How can I ensure air balance between the adjacent zones? Can I take the absolute value of this air flowrate as air flow inputs into BOTH zones, that is the air flow from lower to upper zone equals the air flow from upper to lower zone?

All replies are higly appreciated.

Thanks,
Knut Erik
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