Re: [EnergyPlus_Support] double skin facade

[Pedro Peixeiro <ppeixeiro@xxxxxxx>]

Denis,

I've compared with the work done by Salens 2002, you should easily find his thesis on the web. It was the most extended work I've found about the subject at the time.

For a passive facade and a mechanical ventilated one, coefficients should indeed be different. the adaptive algorithm should give you the ability to control different equations for these different situations. Now, what should you use, I don't know exactly. I would say that Saelens has information about algorithms for these two situations as well, though I can't say for certain, been a while since I looked at these matters. Note that if you wish to model a facade with the added effect of mechanical and natural ventilation, a good aproximation would be to only look at the mechanical effect, since the induced air velocity due to buoyancy is, in normal circunstances, much smaller than the first, and would be considerably easier to assess since you control the air velocity values through mechanical ventilation. Wish you a good work.

Pedro.


On 18-07-2012 13:15, Denis Piccoli wrote:

 

Thank you Pedro

For natural ventilation cavity the ISO15099Windows is the best approximation. how do you evaluate this? Can you explain me which comparisons have you made?

I would model a double facade that in winter is close(passive facade) while in the summer there is a mechanical ventilation. The 2 covection coefficients are different. How E+ takes account? I think that only way is to use adaptive convection algorithm.

thanks

2012/5/31 Pedro Peixeiro <ppeixeiro@xxxxxxx>

I think what Jason meant is that if the zone being served by the facade (and not the facade zone itself) is occupied, you should model it as an independent zone, together with airflow network.

There is some literature about the covection coefficients in a DSF, but E+ doesn't have an algorithm that applies directly to this case. From the comparisons that I've made, the ISO15099Windows, found in the adaptive convection algorithm, seems to be the one that better aproximates some of the propososed models for the inside convection.

Pedro.

On 31-05-2012 8:02, Denis Piccoli wrote:

 

Thank you Jason

Actually my Double skin facade is a box window but to simplify the simulation I modeled it as a corridor facade.

The cavity is not a occupiable space, it is only 110 mm wide.

In this case I think that the best thing is to model with  WindowProperty:AirflowControl 

2012/5/30 Jason Kirkpatrick <jason.alan.kirkpatrick@xxxxxxxxx>

If your double wall cavity is truly a corridor and is occupiable space included in ventilation calculations and having its own air terminals, then you will want it to be modeled as its own thermal zone.

If this is not occupiable space,  you may be making the model unnecessarily complex by modeling the cavity as a separate zone.

I would suggest looking into the WindowProperty:AirflowControl & WindowProperty:ShadingControl to see if the options shown there represent your cavity airflow and shading. If yes then you could just model as a wall with a construction with 1.1 m air gap.

If you do end up with the cavity having its own thermal zone, and you want to pass light through this thermal zone to model daylighting sensors on the interior, you will need to model all thermal zones as convex. A formal definition of convex is that any straight line passing through the zone intercepts at most two surfaces. 

Hope this helps.

Jason

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