[Greenbuilding] Windah tahk (was Re: passive house in NY)

[RT]

On Thu, 27 Oct 2011 22:22:17 -0400, Reuben Deumling <9watts at gmail.com>  
wrote:

> thermal benefits notwithstanding... the high-tech sealed units fail
> after as little as 20 years and then one no longer has a clear window to
> look through.
> fogging of two single pane sashes...but on my crummy houses original  
> windows plus storm sashes
> this has never to my knowledge occurred.


If condensation between the single-glazed, old windows and (outside)  
storms has never occurred, I'd venture that it's likely because the storms  
don't provide a very good air seal, allowing vapour between the panes to  
escape to the atmosphere before condensation occurs.

While that might be considered a Good Thing WRT for maintaining  
visibility, probably not so good for minimising heat loss.

Further, the air space between the old windows and the storms is typically  
in the order of "inches" rather than the fraction of an inch that is  
typical of sealed units.

The smaller fraction-of-an-inch airspace helps to minimise the convection  
between the sometimes-extremely-cold outer pane and warmer inner pane --  
convection that accelerates heat loss beyond what would have occurred with  
just conduction. I suspect that a heat-loss analysis for the house would  
reveal alarming (to Reuben) numbers for those windows.

That being said, I hardly should be the one spouting the sealed IGU  
religion since on my own house I have just three sealed IGUs (one on a  
store-bought terrace door and two in a patio door), the rest being Pella  
[spit] windows with the removeable inner pane (for windows with operable  
sash, interior screens being replaced with interior storms in winter) and  
multiple-pane with dry seals made from stock-size single panes of tempered  
patio door glass (ie for large areas of glazing on attached sunspace),  
interior pane treated as air barrier with small gap left at top of rubber  
glazing channel gasket (where the ends meet) on the exterior pane to serve  
as a breather vent. True, those breather vents sometimes becomes an inlet  
for vapour during the warm, humid, summer months but fortunately in this  
climate, those times are brief and the moisture cooks off quite easily.  
Further, the dry seals allow for quick/easy demounting of the outer panes  
for maintenance as required.

But what I had wanted to mention (before wandering off on the above  
tangent) was the the sealed IGUs are still the originals that were in the  
doors when they were installed almost three decades ago.

I attribute the longevity of the seals to having minimised their exposure  
to temperature extremes due to summer sun, the openings having been  
provided with overhangs scaled to provide full summer shading.

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada

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