[Greenbuilding] apples, oranges, and u values

[stephen at thermotechfiberglass.com]

Well RT, from one older guy to another - that 12+yr old memory that was 
pretty good.

For anyonne who wants a longer version of the story:

I was in Houston at The BIG National Home Builders Show. I was in the 
booth of our lineal supplier. A tech person from a very BIG Window Maker 
(say - West Coast Competitor M), also a customer of our lineal supplier 
was int he same booth. He was saying how they just moved into the Denver 
market and they were getting condensation at the bottoms of their jambs 
(on the roomside face), in a few (not all) houses.

He knew it wasn't really the fault of the fglass because it was always 
the same part of the frame (not some random location), but he didn't 
really know what was going on.

Compared to vinyl fglass is strong like bull, so there are few if any 
internal multi-chamber honeycomb type walls. The frame sections are kind 
of tube-like. My guess is that in moving from a warmer West Coast 
climate to a colder Denver climate they were now seeing the effects of 
natural convection within the jamb. Just like you can get condensation 
at the bottom of a insulating glass unit - which is kind of a big open 
tube - they were getting condensation at the bottom of a jamb - which is 
kind of a big open tube.

One way to stop the condensation is to supress the natural convection 
with insulation. In a double glazed window, like those made by West 
Coast Competitor M, an insulated frame does not really change Uwindow, 
but it sure as heck could eliminate condensation on the frame.


In the intervening years.....
1. Cost cutting measures by some vinyl window makers mean more and more 
internal walls are being removed, making their frames more tube-like. I 
expect some of them are experiencing condensation on their frames.
2. Some fiberglass frames that formerly had open backs (which made it 
easy to verify that the frames were in fact insulated) are now made w/ 
closed backs. While stronger the closed back frames make it harder to 
verify the existence of any claimed insulation. Although condesation at 
the bottom of the jamb would be a strong hint that it might not be 
there.
3. RT's memory is as strong as ever.

thx
Stephen
Thermotech Fiberglass Fenestration


On 2012-04-16 17:23, RT wrote:
> On Mon, 16 Apr 2012 11:46:27 -0400, John Straube
> <jfstraube at uwaterloo.ca>  wrote:
>
>> The Europeans DO measured U-value differently.
>> They measure at an outdoor temperature of 32 F.  The result is 
>> slightly  higher R-value / lower U-values and slightly wider optimum 
>> air gaps.   They also design their hollow frames with larger voids as 
>> convection  does not set in as quickly.
>> As a rule of thumb, I derate their R-values by 10% relative to NFRC,
>
> Speaking of hollow voids, just to spread the slamming of window
> manufacturers from other countries around a bit ...
>
> I have vague memories of a story that Stephen Thwaites (another
> enginoid  whose alma mater is Univ of Waterloo, where WatJohn hangs
> his hat when  he's in Canada) had told me about 12 or more years ago 
> (
> memory dim &  noggin full of cobwebs so specifics may be a bit off).
>
> I think the story was that Stephen was down at a window
> manufacturers'  conference (trade show ?) somewhere in the US (SW ?)
> and one of the  manufacturers who also supplied pull-truded 
> fibreglass
> frame windows like  Stephen's company Thermotec Windows
> http://www.thermotechfiberglass.com/   was puzzled as to why their
> windows weren't performing as well as they  might (I don't remember
> the specifics but probably compared to  Thermotech's) in cold climate
> applications.
>
> To cut to the chase, it didn't occur to the US manufacturer to fill
> the  hollow cores of the fibreglass lineals with insulation, like
> Thermotech  did with theirs.  D'oh!
>
> (Here's hoping Stephen sees this posting and sets the story straight
> where  I may have "mis-remembered" some details.)