[Bldg-sim] Vertical butt joint glazing - thermal bridging

[Graham Carter & Megan Lyall]

Chris,
We had a look at this recently.  For a curtainwall system with panels  
captured on two sides by a non-thermally broken aluminium mullion and  
structurally glazed (butt joint) on the other two showed a  
theoretical overall vision panel of 2.1 W/m2 oK for a system with a  
COG U-Value of 1.7 (divide by 5.678 for IP) according to the  
consultant using Therm and Window 5.2.  The high values in the ASHRAE  
handbook (2.6-2.8) I believe reflect a larger frame area ...
G

On 15/05/2008, at 11:46 PM, Vikram Sami wrote:

> Neeraj is correct regarding the size (and aspect ratio) of the pane  
> making a difference. Essentially - the ratio of perimeter to area s  
> a bid riving factor. I think you could arrive at the overall U- 
> value using Window 5.2 by LBNL - it allows for different window  
> sizes, and you can customize your frame conductance.
>
> With regards to frame conductance, most manufacturers will give you  
> those numbers if you ask them - they should have it for butt glazed  
> systems too (I assume you mean structural silicone glazing where  
> the frame is behind the glass).
>
>
>
> Vikram Sami, LEED AP
> Direct Phone 404-253-1466 | Direct Fax 404-253-1366
>
> LORD, AECK & SARGENT ARCHITECTURE
> Responsive Design · Technological Expertise · Exceptional Service
> www.lordaecksargent.com
>
> ________________________________
>
> From: bldg-sim-bounces at lists.onebuilding.org on behalf of Neeraj  
> Kapoor
> Sent: Thu 5/15/2008 00:29
> To: Chris Jones; bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Vertical butt joint glazing - thermal bridging
>
>
>
> Hello Chris,
>
> Seems like you would need to (appropriately) average out "edge of
> glass"
> and "center of glass" u-values. This may be a function of the size of
> the glass plane, i.e. a large glass plane will have predominantly
> "center of glass" u-value characteristics rather than "edge of glass".
> My question back to the bldg-sim(ers) will be -- are there any studies
> /
> empirical data drawing relationship between edge effects and center of
> glass conductance values with respect to different types of glazings
> and
> their sizes.
>
> ~Neeraj
>
> Neeraj Kapoor
> t: +91-99581.70018
> Kalpakrit Sustainable Environments Pvt. Ltd.
> New Delhi
>
>
> Chris Jones wrote:
>> A client has a project with the glazing units butt jointed at the
>> vertical joints between sections.  He thinks that this may have less
>> thermal bridging then for a vertical joint with typical framing
>> details.  Does any one have any experience with this type of joint?
>> The glazing units are double pane sealed units with warm edge
> spacers.
>>
>>
>>
>> Chris Jones, P.Eng.
>> 14 Oneida Avenue
>> Toronto, ON M5J2E3
>> Tel. 416 203-7465
>> Fax. 416 946-1005
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