<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 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 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 href="mailto:massucci@gmail.com">massucci@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;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></div><div class="h5"><br><div class="gmail_quote">On Tue, May 10, 2011 at 5:10 AM, Chris Yates <span dir="ltr"><<a href="mailto:chris.malcolm.yates@gmail.com" target="_blank">chris.malcolm.yates@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;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></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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</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>
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