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

[Francisco Massucci]

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>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> 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
>>
>> Skype: christopher.m.yates
>>
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