Simulating Curtain Wall in Energy Plus.

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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

srishti srivastava's picture
Joined: 2011-10-02
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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 Yates

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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 fa?ade using the "exterior
vented natural cavity." *
*The fa?ade 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 fa?ade. 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

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Joined: 2011-10-02
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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 fa?ade using the "exterior
vented natural cavity."
The fa?ade 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 fa?ade. 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 fa?ade as
exterior vented cavity
and the other with the fa?ade 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 fa?ade,
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 fa?ade 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 fa?ade 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 Fa?ades (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 Fa?ades. 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.

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Joined: 2011-10-02
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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.

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Hi Pedro,

Thanks for this - it's good to be up to date with the latest E+
developments and this is a significant one.

I'm not certain Srishti was asking about ventilated facades in the first
instance. I just threw it in there in my first response and the thread
has seemed to grow into a "ventilated facades" discussion!

Best regards

Chris Yates

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Thanks to all,

I would like to clarify the approach i have taken in the study at this
point of time.

The Building which is modelled is a sqaure block. There are five zones
(four aligned in the cardinal directions and one in the centre), the
depth of the zone is till 15 feet from the facade in each cardinal
direction.

Firstly, I am considering a glazed facade here, which might be either
monolithic(one layer of glass) or Insulated Glazed Units (Double
layers of glass 6 mm thick with an air gap of 12 mm sandwitched
between them ). It is not a load bearing structure.There is no
insulation separately used in the facade.

Secondly, the glass is attached to the subframe which is subsequently
attached to the main frame(both of which are aluminium). Or it can be
directly attached to main frame.

In short, the facade which needs to be simulated is not an opaque
construction. Infact, it is fully glazed since i m considering a
window wall ratio as high as 90 percent also as one of the variables
in the study.

Thus, the question remains to be the same.
How to model curtain wall or rather curtain glazed facades in Eplus?
How will the modelling for such type of facade be different from
modelling a regular window?

I really appreciate the time spent and effort made by people reading
and replying to the thread.

Srishti.

srishti srivastava's picture
Joined: 2011-10-02
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Srishti,

This is nothing out of the ordinary. Just use E+ standard fenestration
objects.

You're using Window. My approach would be to build up my glazing in
Window, check it's performance and then manually transfer its
performance data to the objects WindowMaterial:Glazing,
WindowMaterial:Gas & Construction. There does appear to be an option to
link with Window via Construction:WindowDataFile. I have not tried this yet.

Best of luck

Chris Yates

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Chris,

I have tried the option to link with Window via Construction:WindowDataFile,
it works fine with the windows with frame and glass but with curtain glazing
there are problems in modeling the window in therm and importing it in
energy plus(This is the reason why i was asking to directly model it in
Energy Plus in my first mail itself.)

Thanks for the other suggestion of doing it in window and manually
transferring the values into Energy Plus model, I will try that out and get
back soon.

Thanks Again,
Srishti.

srishti srivastava's picture
Joined: 2011-10-02
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Hi Srishtri,

I suggest looking at the WindowProperty:FrameAndDivider and
FenestrationSurface:Detailed topics in the Eplus input/output reference
documentation. You can find an example of these inputs in the file
AirflowNetwork_MultiZone_SmallOffice.idf.

Shaun

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