[Bldg-sim] Simulating Curtain Wall in Energy Plus.
Chris Yates
chris.malcolm.yates at gmail.com
Wed May 11 09:22:21 PDT 2011
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
On 10/05/2011 14:47, Pedro Peixeiro wrote:
> 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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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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