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Hello everyone.<br>
<br>
Chris,<br>
<br>
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:<br>
1) they cannot be specificied to occupy just a fraction of the
glazing area (fully deployed or no shading at all);<br>
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;<br>
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).<br>
<br>
Srishti,<br>
<br>
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.<br>
<br>
Pedro.<br>
<br>
<br>
On 10-05-2011 12:32, Francisco Massucci wrote:
<blockquote
cite="mid:BANLkTinRZEuZoNyfBSbcT32nGgc7N3yYbA@mail.gmail.com"
type="cite">
<div>Srishti,</div>
<div><br>
</div>
<div> Here is the entire text. My ctrl+C, Ctrl+v failed last
time, sorry.</div>
<div><br>
</div>
<div><b>SIMULATING DOUBLE SKIN FACADE</b> <br>
<br>
</div>
<div>I'm simulating an office with a double skin façade using the
"exterior vented natural cavity." </div>
<div>The façade is naturally ventilated and has Venetian blinds in
the gap. The blinds are exposed to solar </div>
<div>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 </div>
<div>account these two effects? </div>
<div><br>
</div>
<div><b>Answer</b> </div>
<div>The exterior vented natural cavity model is for *opaque*
surfaces only and does not apply to glazing </div>
<div>systems. There is a model for blinds in the window gap that
takes those two things into account, but I </div>
<div>am not sure if it works together with the air flow window
model. </div>
<div><br>
</div>
<div><b>Question</b> </div>
<div>Thanks for your answer. I compared two simulations, one with
the façade as exterior vented cavity </div>
<div>and the other with the façade as a simple window, and it
seemed that solar transmission through the </div>
<div>glazing system is the same in both the cases. Even if the
exterior vented cavity is only for opaque </div>
<div>surfaces do you think it is possible to use the model for a
glass façade, using as input the data of the </div>
<div>glazing system (thermal emissivity and solar absorbtivity)?
Which differences or errors would occur </div>
<div>using that model? </div>
<div><br>
</div>
<div><b>Answer </b></div>
<div>If I understand you correctly, I think what you are actually
getting in the model is a regular window </div>
<div>surrounded by a wall with a double skin. See if the inside
face wall surface temperatures are different. </div>
<div>The window shouldn't be changing. </div>
<div>The exterior vented cavity model, which assumes that all the
solar is blocked by a thin, solid layer on </div>
<div>the outside, cannot be used for glazing. Opaque means no
transmission. Inside EnergyPlus this </div>
<div>becomes a special boundary condition for surface heat
transfer modeling that is not available for </div>
<div>window modeling. The window still gets exterior environment
boundary conditions even though its </div>
<div>
parent surface has the exterior cavity boundary condition. </div>
<div>Double façade improvements are being planned for the future.
</div>
<div><br>
</div>
<div><b>Possible Workaround </b> </div>
<div>if you really wanted to use the exterior vented cavity model
on your DF, it could apply to a case where </div>
<div>the double façade has totally opaque shades that are closed
tight. You would use regular materials in </div>
<div>the construction for the surface that approximate the DF (no
subsurface and no glazing materials). </div>
<div>The baffle in the exterior cavity model can get quite hot and
then re-radiate infrared (but no </div>
<div>shortwave) and convect to the underlying surface. But note
that air gap models are much better </div>
<div>developed for windows than for regular constructions; you
would have to come up with thermal </div>
<div>properties for each layer. One advantage of this approach
might be a better model of transient </div>
<div>behavior because the window models are always steady state. </div>
<div>See also: EnergyPlus Technical Note – Opaque Ventilated
Façades (July 2007 User News)</div>
<div>On May 28, 2007, Emanuele Naboni (PhD Candidate), a visiting
researcher from the Politecnico di </div>
<div>Milano (Italy) gave a lecture at Lawrence Berkeley National
Laboratory on how he used EnergyPlus to </div>
<div>
model Ventilated Opaque Façades. A .pdf of his presentation is
available at </div>
<div><a moz-do-not-send="true"
href="http://SimulationResearch.lbl.gov/reports.html">http://SimulationResearch.lbl.gov/reports.html</a>
under the heading "All EnergyPlus Reports." </div>
<div>To save time, here is the direct link: <a
moz-do-not-send="true"
href="http://simulationresearch.lbl.gov/dirpubs/vent_facade.pdf">http://simulationresearch.lbl.gov/dirpubs/vent_facade.pdf</a>
</div>
<div><br>
</div>
<div><br>
</div>
<div>Francisco Massucci.</div>
<br>
<div class="gmail_quote">On Tue, May 10, 2011 at 8:21 AM,
Francisco Massucci <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:massucci@gmail.com">massucci@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
<span style="border-collapse: collapse; font-family:
arial,sans-serif; font-size: 13px;">Srishti,</span>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;"><br>
</span></font></div>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;"> 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.</span></font></div>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;"><br>
</span></font></div>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;"> I found something on
google, someone asking for an energyplus's developer:</span></font></div>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;"><br>
</span></font></div>
<div><font face="arial, sans-serif"><span
style="border-collapse: collapse;">
<div>
<i>I'm simulating an office with a double skin façade
using the "exterior vented natural cavity." </i></div>
<div><i>The façade is naturally ventilated and has
Venetian blinds in the gap. The blinds are exposed
to solar </i></div>
<div><i>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 </i></div>
<div><i>account these two effects? </i></div>
<div><i>Answer </i></div>
<div><i>The exterior vented natural cavity model is for
*opaque* surfaces only and does not apply to
glazing </i></div>
<div><i>systems. There is a model for blinds in the
window gap that takes those two things into account,
but I </i></div>
<div><i>am not sure if it works together with the air
flow window model.</i></div>
<div><i><br>
</i></div>
<div>Please let me know if you do some progress. I'm
from Brazil and our climate conditions are very
similar.</div>
<div><br>
</div>
<div>Good Luck,</div>
<div><br>
</div>
<font color="#888888">
<div>Francisco Massucci</div>
</font></span></font>
<div>
<div class="h5"><br>
<div class="gmail_quote">On Tue, May 10, 2011 at 5:10
AM, Chris Yates <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:chris.malcolm.yates@gmail.com"
target="_blank">chris.malcolm.yates@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt
0pt 0.8ex; border-left: 1px solid rgb(204, 204,
204); padding-left: 1ex;">
<div bgcolor="#ffffff" text="#000000"> Srishti,<br>
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.<br>
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.<br>
Good luck<br>
Chris
<div>
<div><br>
<br>
On 10/05/2011 06:58, srishti srivastava wrote:
<blockquote type="cite">
<pre>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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</blockquote>
<br>
</div>
</div>
<div>-- <br>
<div>
<p>Chris Yates <span style="color: rgb(79,
98, 40);">C Eng MCIBSE</span></p>
<p><i>Building Physics Consultant</i></p>
<p>Tel:<span> </span>+447960731576</p>
<p>Email: <a moz-do-not-send="true"
href="mailto:chris.malcolm.yates@gmail.com"
target="_blank">chris.malcolm.yates@gmail.com</a></p>
<p>Skype: <span>christopher.m.yates</span></p>
</div>
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</blockquote>
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<br>
</div>
</div>
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</blockquote>
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<br>
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