[esp-r] Re: Low-e coatings
Bart Lomanowski
blomanow at engmail.uwaterloo.ca
Thu Mar 13 20:35:53 GMT 2008
Hi Liam,
U values for center-of-glass windows are calculated based on certain
environmental conditions (eg. ASHRAE winter condition) as a rating
method by adding up the total resistance accross a window. However, in
reality, these individual resistances (convective and radiative) are
temperature dependent. By tweaking the Rgap value to match the WINDOW5
U-value, you are in fact accounting for the low-e coating in an
approximate way. BUT, from an energy simulation point of view, to
properly account for the low-e coating, the temperature dependency of
the gas gap resistance should be known. That being
said, the Rgap value probably doesn't change that much so as an
approximate method, I don't think it's that bad.
As for my work, I am adding a more accurate treatment of windows
with/without venetian blind shading layers in any configuration
(outside, inside, between-the-glass). This method accounts for
temperature dependence of individual resistances, and solves for gas
gap resistances on a time-step basis. The model also includes dynamic
slat control of venetian blinds on a time-step basis, allowing for
implementation of real-time shading control schemes (eg. solar
tracking). The front end of my model is a graphical Glazing/Shading
Editor developed by John Wright which allows the user to very quickly
generate a complex glazing unit with any combination of fill gases,
coatings and four
different types of shading layers (restricted to venetian blinds for
ESP-r use, for now). This work will be merged into the general release
of ESP-r this summer.
Hope that helps,
Bart
---
Bartosz Lomanowski
MASc Candidate
Solar Thermal Research Lab
Department of Mechanical Engineering
University of Waterloo
200 University Avenue West
Waterloo, Ontario, Canada N2L 3G1
+1 519 888 4567 x33885
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> Today's Topics:
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> 1. Low-e coatings (Liam O'Brien)
> 2. Low-e coatings (Liam O'Brien)
> 3. RE : Low-e coatings (Denis J. Bourgeois)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 12 Mar 2008 17:51:24 -0400
> From: Liam O'Brien <obrien_liam at hotmail.com>
> Subject: [esp-r] Low-e coatings
> To: <esp-r at lists.strath.ac.uk>
> Message-ID: <BAY122-W40B2F01DDA2B5CAE6BAB3B84080 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
>
>
> Hello,
>
> I want to model a low-e coating on a new window construction. As
> far as I can tell, materials (i.e. glass) are defined as homogeneous
> in the materials library, and thus have a single emissivity value.
> However, clearly a low-e coating will cause the glass to have two
> different emissivity values. Could anyone share how they have
> modeled this?
>
> Also, it would be useful in future versions of ESP-r to have fill
> gases other than air. I know the properties of the air can be
> changed, but it would save a step to be able to choose argon or
> krypton, for example.
>
> Thanks!
>
> Liam O'Brien
>
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>
> Message: 2
> Date: Wed, 12 Mar 2008 18:00:23 -0400
> From: Liam O'Brien <obrien_liam at hotmail.com>
> Subject: [esp-r] Low-e coatings
> To: <esp-r at lists.strath.ac.uk>
> Message-ID: <BAY122-W41BA00D1C3E902E3055FE884080 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
>
>
> Hello,
>
> I want to model a low-e coating on a new window construction. As
> far as I can tell, materials (i.e. glass) are defined as homogeneous
> in the materials library, and thus have a single emissivity value.
> However, clearly a low-e coating will cause the glass to have two
> different emissivity values. Could anyone share how they have
> modeled this?
>
> Also, it would be useful in future versions of ESP-r to have fill
> gases other than air. I know the properties of the air can be
> changed, but it would save a step to be able to choose argon or
> krypton, for example.
>
> Thanks!
>
> Liam O'Brien
>
> _________________________________________________________________
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> http://g.msn.ca/ca55/208
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> ------------------------------
>
> Message: 3
> Date: Wed, 12 Mar 2008 18:25:45 -0400
> From: "Denis J. Bourgeois" <Denis.Bourgeois at arc.ulaval.ca>
> Subject: [esp-r] RE : Low-e coatings
> To: "Liam O'Brien" <obrien_liam at hotmail.com>,
> <esp-r at lists.strath.ac.uk>
> Message-ID:
> <DF36C80B7884EE4A86EB6FD397921C385394B7 at exch-be02.ulaval.ca>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Liam,
>
>
>
> The radiation exchanges between surfaces separated by an air gap
> within a construction are not explicitly modelled / simulated in
> ESP-r - rather the effective thermal resistance of the air gap in
> the zone's construction file (.con) can be adjusted to account for
> various gases and low-e coatings in a sealed glass unit. Using WIS
> or LBNL's WINDOW, you can derive the effective gap resistance for a
> given window from the entire unit U value, and individual glass pane
> thicknesses and conductivities. You should also tweak values to
> account for framing effects (both in .con and .tmc files).
>
>
>
> Hope this helps,
>
> Denis Bourgeois
>
>
>
> -----Message d'origine-----
> De : esp-r-bounces at lists.strath.ac.uk
> [mailto:esp-r-bounces at lists.strath.ac.uk] De la part de Liam O'Brien
> Envoy? : March 12, 2008 5:51 PM
> ? : esp-r at lists.strath.ac.uk
> Objet : [esp-r] Low-e coatings
>
>
>
> Hello,
>
> I want to model a low-e coating on a new window construction. As
> far as I can tell, materials (i.e. glass) are defined as homogeneous
> in the materials library, and thus have a single emissivity value.
> However, clearly a low-e coating will cause the glass to have two
> different emissivity values. Could anyone share how they have
> modeled this?
>
> Also, it would be useful in future versions of ESP-r to have fill
> gases other than air. I know the properties of the air can be
> changed, but it would save a step to be able to choose argon or
> krypton, for example.
>
> Thanks!
>
> Liam O'Brien
>
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