[Greenbuilding] Passive House Overheating

Corwyn corwyn at midcoast.com
Wed Aug 15 17:34:42 PDT 2012


On 8/15/2012 1:59 PM, John Straube wrote:
> Exterior shading of 24" overhanging a 8-9' high wall works, maybe, May
> June July but does not help in April or September.  These are the bigger
> problems, as these months one can often have outdoor temperatures of 65
> to 75 and full 200 Btu/hr/ft2 sun hitting windows.
> Exterior shades are absolutely the answer. Unless you have a working
> couple in the home who are not in the house during sunny hours.  I guess
> that is unlikely, eh?  This can be solved with automatic controls on
> automated shades. If you want to spend that kind of money.
>
> Orrr, you could just use lower SHGC windows.  But if you want to hit a
> magic space heating (rather than total energy use) target using an
> imprecise program (like PHPP) then I suppose that simple and low cost
> solution wont work :)

"Just" using lower SHGC windows, increases energy needed for heating. 
It is a trade-off.  Opening windows at night (and other such measures) 
does NOT increase winter heating requirements.  I would say that those 
should be where we start.

For this house, halving the SHGC on the windows, would lose 5M BTUs or 
so, at a cost of around $120 per year.  I will note that my simulation 
shows that the worst overheating is in the spring, by the time the trees 
have leaved out, the problem is lessened.


Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652



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