[Bldg-sim] Simulating Curtain Wall in Energy Plus.

Pedro Peixeiro ppeixeiro at lnec.pt
Tue May 10 06:47:50 PDT 2011


Hello everyone.

Chris,

That limitation isn't present anymore. Solar radiation is partially 
absorbed by the interzone ceilling and floor (and eventually walls if 
present) but calculation is carried out to transmit the remaining 
diffuse and direct radiation into the subsequent zone. Reflections are 
also taken into account. But limitations still persist about shading 
devices:
1) they cannot be specificied to occupy just a fraction of the glazing 
area (fully deployed or no shading at all);
2) they can only be mounted on windows of exterior walls (though this 
allows to model the shading device before, after and in between double 
glazed windows of the exterior pane, it can't be be modeled for shading 
devices on the inner pane, room side;
3) there is still some limitations regarding airflow and convection 
coefficient control between the shading device and the glazing itself, 
because Eplus considers the shading device as a layer of the window it 
is mounted on, and no direct control can be done for that in-between 
window/shade air gap (this also prevents output results for the interior 
window surface of the outside pane, only outside surface temperature and 
shading temperature can be obtained).

Srishti,

So like it has been said, if you plan on simulating ventend facades in 
which the inside pane is opaque, you can model them using the Exterior 
Natural Vented Cavity object present in Eplus. If not, my advice is to 
setup your facade as a vertical stack of two or more zones divided by 
virtual partitions. Using Airflow Network objects, you can define all 
the air dampers you need on the outside pane and also the ventilation 
that occurs across the virtual partitions. Use Full Interior and 
Exterior Solar Distribution with Reflections (remember to keep your zone 
convex), choose a proper inside convection algorithm for the cavity (I 
suggest ISO 15099 Windows), and you should come across some relatively 
close results, considering the complexity of the problem itself.

Pedro.


On 10-05-2011 12:32, Francisco Massucci wrote:
> Srishti,
>
>   Here is the entire text. My ctrl+C, Ctrl+v failed last time, sorry.
>
> *SIMULATING DOUBLE SKIN FACADE*
>
> I'm simulating an office with a double skin façade using the "exterior 
> vented natural cavity."
> The façade is naturally ventilated and has Venetian blinds in the gap. 
> The blinds are exposed to solar
> radiation and, during the day, they can reach very high temperatures 
> which may affect the temperature of the air in the gap and/or the 
> performance of the glass façade. Does EnergyPlus take into
> account these two effects?
>
> *Answer*
> The exterior vented natural cavity model is for *opaque* surfaces only 
> and does not apply to glazing
> systems. There is a model for blinds in the window gap that takes 
> those two things into account, but I
> am not sure if it works together with the air flow window model.
>
> *Question*
> Thanks for your answer. I compared two simulations, one with the 
> façade as exterior vented cavity
> and the other with the façade as a simple window, and it seemed that 
> solar transmission through the
> glazing system is the same in both the cases. Even if the exterior 
> vented cavity is only for opaque
> surfaces do you think it is possible to use the model for a glass 
> façade, using as input the data of the
> glazing system  (thermal emissivity and solar absorbtivity)? Which 
> differences or errors would occur
> using that model?
>
> *Answer *
> If I understand you correctly, I think what you are actually getting 
> in the model is a regular window
> surrounded by a wall with a double skin. See if the inside face wall 
> surface temperatures are different.
> The window shouldn't be changing.
> The exterior vented cavity model, which assumes that all the solar is 
> blocked by a thin, solid layer on
> the outside, cannot be used for glazing. Opaque means no transmission. 
> Inside EnergyPlus this
> becomes a special boundary condition for surface heat transfer 
> modeling that is not available for
> window modeling. The window still gets exterior environment boundary 
> conditions even though its
> parent surface has the exterior cavity boundary condition.
> Double façade improvements are being planned for the future.
>
> *Possible Workaround *
> if you really wanted to use the exterior vented cavity model on your 
> DF, it could apply to a case where
> the double façade has totally opaque shades that are closed tight. You 
> would use regular materials in
> the construction for the surface that approximate the DF (no 
> subsurface and no glazing materials).
> The baffle in the exterior cavity model can get quite hot and then 
> re-radiate infrared (but no
> shortwave) and convect to the underlying surface. But note that air 
> gap models are much better
> developed for windows than for regular constructions; you would have 
> to come up with thermal
> properties for each layer. One advantage of this approach might be a 
> better model of transient
> behavior because the window models are always steady state.
> See also: EnergyPlus Technical Note – Opaque Ventilated Façades (July 
> 2007 User News)
> On May 28, 2007, Emanuele Naboni (PhD Candidate), a visiting 
> researcher from the Politecnico di
> Milano (Italy) gave a lecture at Lawrence Berkeley National Laboratory 
> on how he used EnergyPlus to
> model Ventilated Opaque Façades.  A .pdf of his presentation is 
> available at
> http://SimulationResearch.lbl.gov/reports.html under the heading "All 
> EnergyPlus Reports."
> To save time, here is the direct link: 
> http://simulationresearch.lbl.gov/dirpubs/vent_facade.pdf
>
>
> Francisco Massucci.
>
> On Tue, May 10, 2011 at 8:21 AM, Francisco Massucci 
> <massucci at gmail.com <mailto:massucci at gmail.com>> wrote:
>
>     Srishti,
>
>       Try to found a topic named "Double Facades" on bldg-sim list. I
>     asked the same question some time ago.  The major problem in this
>     cases ,is the heat loss by convection inside de facade, because
>     otherwise it will percfectly work as a thin zone.
>
>      I found something on google, someone asking for an energyplus's
>     developer:
>
>     /I'm simulating an office with a double skin façade using the
>     "exterior vented natural cavity." /
>     /The façade is naturally ventilated and has Venetian blinds in the
>     gap. The blinds are exposed to solar /
>     /radiation and, during the day, they can reach very high
>     temperatures which may affect the temperature of the air in the
>     gap and/or the performance of the glass façade. Does EnergyPlus
>     take into /
>     /account these two effects? /
>     /Answer /
>     /The exterior vented natural cavity model is for *opaque* surfaces
>     only and does not apply to glazing /
>     /systems. There is a model for blinds in the window gap that takes
>     those two things into account, but I /
>     /am not sure if it works together with the air flow window model./
>     /
>     /
>     Please let me know if you do some progress. I'm from Brazil and
>     our climate conditions are very similar.
>
>     Good Luck,
>
>     Francisco Massucci
>
>     On Tue, May 10, 2011 at 5:10 AM, Chris Yates
>     <chris.malcolm.yates at gmail.com
>     <mailto:chris.malcolm.yates at gmail.com>> wrote:
>
>         Srishti,
>         I have no experience of the Therm/ LBNL Window link that you
>         speak of but as long as you're happy with working within the
>         limitations of the E+ shading calculation you should be fine.
>         I'm not sure of the latest E+ but the main historical
>         limitation I'm aware of is that solar gain to a zone is
>         absorbed by the floor (with some specific exceptions). This is
>         expedient for most simulation tasks but will not suffice if
>         you wish to model solar penetrating through subsequent zones
>         (within a double sheet facade, where the cavity is modelled as
>         a zone for example). The E+ documentation is extensive and
>         covers this in detail.
>         There are a number of options for the type of solar calc
>         undertaken. There are also options for convection coefficient.
>         You may find both of these affect results and simulation time.
>         Good luck
>         Chris
>
>
>         On 10/05/2011 06:58, srishti srivastava wrote:
>>         Dear Friends,
>>
>>         I am Srishti Srivastava from India. My research topic is related to
>>         evaluation of different types of facades in Indian context with
>>         special reference to the modern glazed facades.
>>
>>         I am trying to simulate a building with curtain wall in Energy Plus. I
>>         know of one way of doing it through Window and Therm software from
>>         LBNL, although there are few issues in that. Is there any alternative
>>         way to simulate curtain wall in Energy Plus.
>>
>>         Does anyone have a prior experience of simulating curtain wall in
>>         Energy Plus. Can anyone help me in simulating a curtain wall in Energy
>>         Plus.
>>
>>         Thanks in advance.
>>
>>         Srishti Srivastava,
>>         India.
>>         _______________________________________________
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>
>         -- 
>
>         Chris Yates C Eng MCIBSE
>
>         /Building Physics Consultant/
>
>         Tel:+447960731576
>
>         Email: chris.malcolm.yates at gmail.com
>         <mailto:chris.malcolm.yates at gmail.com>
>
>         Skype: christopher.m.yates
>
>
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