[esp-r] Re: Emissivity

[Jon Hand]

You are correct that bps is reading the zone construction
files for the emissivity and that you could manually edit
these files (with great fear because it is liable to
being overwritten).  Users used to do such editing
and it often created subtle errors in models so there
are lots of dragons there!

But remember these emissivities are for the front surface
of the whole construction and the back of the whole constuction.
For the case of a single layer construction editing would
be required to get the different properties.  \

And remember that ESP-r does not use the emissivity
at each side of an air gap - it uses an air gap resistance.
I believe that someone is working on code to explicitly
model the radiant transfer in an air gap.

-Jon Hand


-----Original Message-----
From: esp-r-bounces at lists.strath.ac.uk on behalf of Ery Djunaedy
Sent: Thu 5/29/2008 9:59 PM
To: ESP-r User Forum
Subject: [esp-r] Re: Emissivity
 
Jon,

I do not think the bps refers to the materials database directly. There 
are two lines in the CON file that lists the internal and external 
emissivity of every surface. These two lines are created and updated 
through the prj, which refers the number from the materials database. 
During the simulation bps only refers to these two lines, and not to the 
materials database.

My point is, theoretically, we can change the emissivity values in the 
CON file to have different emissivity values for inside and outside 
surface. However, this should be done with two warnings: (1) one should 
know which number belongs to which surface, and (2) whatever changes 
made manually will be overwritten if the CON file is recreated through prj.

Is this a correct short-cut before we have the future versions of ESP-r 
that will allow this to happen through the database?

Thanks,

Ery


Jon Hand wrote:
> A recent question about emissivity (see the email below)...
>
> The listing of data is the optical properties. Optical data
> is only for the visable and shortwave.  Emissivity of a property
> of the materials in the multi-layer construction which is
> associated with this optical property.  The QA report which
> can be generated from within the Project Manager will tell
> you both sets of properties if you toggle the database reporting
> to verbose and select at least one thermal zone which includes
> a construction using this optical attribute.
>
> At the current time, materials in ESP-r have one emissivity
> attribute that applies to both faces of the material. If you
> want each side to have a different emissivity then you have
> to use two adjacent layers/materials.
>
> A future version of ESP-r will use a database structure that
> allows the front and back of a material to have a different
> set of surface properties.
>
> Regards, Jon Hand
>
>
> -----Original Message-----
>
> 1. Would any one of you tell me which part exaclty shows the emmisivity of the following double window?
> =========================================
>
> DCF7671_6omb :Clear float 76/71, 6mm open mid blnd
> # def lyr, tmc lyr, vis trn, sol refl, sol absor, U val
> 1, 5, 0.76, 0.11, 0.28, 2.8
> # direct trn @ 5 angles, total heat gain @ 5 angles
> 0.611, 0.583, 0.534, 0.384, 0.170, 0.711, 0.690, 0.645, 0.487, 0.250
> # refr index, absorption @ 5 angles for each tmc layer
> 1.52, 0.157, 0.172, 0.185, 0.201, 0.202
> 1.00, 0.001, 0.002, 0.003, 0.004, 0.005
> 1.00, 0.172, 0.181, 0.178, 0.151, 0.097
> 1.00, 0.001, 0.002, 0.003, 0.004, 0.005
> 1.52, 0.117, 0.124, 0.127, 0.112, 0.077
> ===============================================
>
>
>
> As far as I know, the emissivity should be described for each single glass.
>
> 2. That means, there should be two emissivity values on in one double window.
> Is it wrong?
>
> Your right answer will be highly appreciated.
>
>
> Lewis Yook
> Team Manager,
> Integrated Simulation Unit.
> Design and Simulation for Sustainability (DASS) consultants Ltd.
>
> 143-834
> Venture Support Center 304-ho
> 632-9 Guui-dong Gwangjin-gu, Seoul, Korea
> T. 82.2.913.2585 F. 82.2.949.2585
> H. www.dasskorea.com
>
>
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>   


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