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RE: R: [EnergyPlus_Support] Vented Facade



Hi, 

The baffle will get all the sun and completely shade the underlying surface.  

There is no need to use "construction with internal source” or “surface:shading:detached:fixed" for this model (but you could if there were other reasons to do so).  

Emanuele,  I don't necessarily see a problem with the temperatures you describe below.  The cavity air temperature can be expected to be lower than two surfaces because of air exchanges with cooler exterior ambient.  The underlying surface's outside face is also exchanging long wave radiation with the hot baffle. So it can get hotter than the cavity air, but this energy isn't from the sun.  Your numbers indicate that radiation heat transfer rate is about twice the convection heat transfer rate, which seems reasonable at these temperatures.  You should also look at an entire day's worth of data on the outside face surface temperature. Because of the transient heat transfer and capacity effects in the underlying surface, it is easy to get missled by data for a single point in time.  

Brent

> -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of fred buhl
> Sent: Friday, March 24, 2006 10:51 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: R: [EnergyPlus_Support] Vented Facade
> 
> 
> Emanuele,
> 
> You probably need to add a shade. The baffle may not automatically 
> generate one.
> Brent probably knows if it does.
> 
> Fred
> 
> Emanuele Naboni wrote:
> 
> >Brent,
> >
> > 
> >
> >In the specific case I’m simulating a simple external 
> surface with thin
> >ceramic and with a gap of 3 inches, that is suppose of 
> generate chimney
> >effects.
> >
> >The not realistic thing is that the temperature of the 
> baffle (ceramic) for
> >example in 21 July at 12 is 80°C, the cavity is 50° and the 
> outside face of
> >the support wall is around 70°C. It seems that the buffle’ 
> protection from
> >the sun isn’t calculated. 
> >
> > 
> >
> >I was wondering if I have to set any parameters in “construction with
> >internal source” or maybe describe the ceramic external layer in
> >“surface:shading:detached:fixed”
> >
> >Thank you very much.
> >
> > 
> >
> >Emanuele, 
> >
> >Which surface temperatures of the support wall are you 
> refering to? inside
> >or outside?   Check what you have set for 
> OutsideFaceEnvironment -- it
> >should be OtherSideConditionsModel
> >
> >Brent
> >
> >
> >
> >-----Original Message-----
> >From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of 
> Emanuele Naboni
> >Sent: Wednesday, March 15, 2006 11:35 AM
> >To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >Subject: Re: [EnergyPlus_Support] Vented Facade
> >
> >
> >Hi everybody,
> >
> >I'm simulting as well an opaque ventilated facade, It works and is
> >very intersting!
> >The baffle and the cavity have very realistic values.
> >
> >The only problem is about the effects it does on the wall 
> where is applied:
> >running a simulation with a vent facade and running another one
> >without vent facade gives the same temperatures on the support wall.
> >have anyone verify that?
> >
> >I'm very intersted too in the Cd values.
> >Emanuele
> >
> >
> >
> >
> >
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