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# double skin facade

I am working on a study that require evaluating the total heat transfer through a ventilated double skin envelope and with the little understand I have so far in OS, am yet to figure out how it can be done. Any help or suggestion will be highly appreciated.

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The way I've done this is to use an EnergyPlus measure to have the exterior walls reference an SurfaceProperty:ExteriorNaturallyVentedCavity object that the measure adds. The object models an opaque surface (if your double skin is glazed then it won't be appropriate), and also only effects opaque exterior surfaces (i.e. won't cover windows).

The measure creates a SurfaceProperty:OtherSideConditionsModel object:

sideConditionModel = "
SurfaceProperty:OtherSideConditionsModel,
ScreenCavityModel,          ! OtherSideConditionsModel Name
GapConvectionRadiation;     ! Type of Modeling used to determine Boundary Conditions
"



then loops through the model surfaces to find exterior walls (by construction or surface type or other criteria of your choice), and assigns the other side condition with

surface.setString(4,"OtherSideConditionsModel")
surface.setString(5,"ScreenCavityModel")


and finally adds the ExteriorNaturallyVentedCavity object:

naturallyVentedCavity = "
SurfaceProperty:ExteriorNaturalVentedCavity,
Vented Cavity Exterior Surface,     ! Name
ScreenCavityModel,          ! OtherSideConditionsModel Object Name
0.02,                       ! Area Fraction of Openings
0.9,                        ! Thermal Emissivity of Exterior Baffle Material
0.92,                       ! Solar Absorbtivity of Exterior Baffle
0.05,                       ! Height scale for bouyancy-driven ventilation
0.05,                       ! Effective Thickness of Cavity Behind Exterior Baffle
0.97,                       ! Ratio of Actual surface area to projected surface area
Smooth ,                    ! Roughness of collector
0.1 ,                       ! Cv, Effectiveness for perforations with respect to Wind
0.5 ,                       ! Cd, Discharge Coefficient for Openings with respect to bouyancy-driven flow
#{surface_names.join(",")} ;   ! Surface Name
"



To find the heat transfer through the object would likely take some creative post-processing, for which I will refer you to the object outputs.

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thank you so much Eric for that insight. I'll try to study these. God bless!

( 2015-07-02 19:50:34 -0600 )edit

I took the liberty of marking this answer as accepted (answered a year and a half ago). @tjolutobi, remember to mark answers as accepted if they solved your problem in the future. Thanks!

( 2017-01-31 07:37:21 -0600 )edit

I am also looking to study the benefits of a double skin facade.By my understanding of the description above, it looks like this can be used only on exterior opaque surface (walls). How would this change and what could I do to study the impacts of the double skin if i were to have the double skin on a curtain wall ? Any help/guidance is appreciated .

( 2017-05-15 11:26:51 -0600 )edit

I think you should open a new question (reference this one).

( 2017-05-19 00:57:29 -0600 )edit

@Eric Ringold your answer from 6 years ago helped me a lot today:) I am modeling the 2nd skin for my single-family house using Energy plus. I have some questions regarding those variables in SurfaceProperty:ExteriorNaturalVentedCavity: - How did you define those variables like Thermal Emissivity, Solar Absorbtivity and etc.? - What is meant by collector here? - What does Surface 1 Name refer to?

( 2021-07-02 08:40:15 -0600 )edit

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