[Greenbuilding] Passive House Overheating

[Jason Holstine]

Sounds to me like an argument for redundancy and flexibility‹ability to
cover the outside or a window then remove it, to cover the inside of a
window then remove, to drink a beverage then remove it...well, this isn¹t
about plumbing....
Doesn¹t excellent design account for redundancy and flexibility, especially
when we have a growing eye toward passive survivability, universal design,
etc? (I vote yeah)


On 8/15/12 5:47 PM, "Alan Abrams" <alan at abramsdesignbuild.com> wrote:

> points well taken--passive solar optimization is never perfect (unless there
> are deciduous trees in play), because the solar cycle is always out of phase
> with seasonal thermal intensity--the hottest months trail the summer solstice,
> etc.
> 
> so if you can't control solar gain otherwise, you have to make a commitment
> whether to favor heat gain or solar shading.  And it may include deciding
> whether to sacrifice some notion of absolute comfort for the sake of reducing
> total annual energy consumption. 
> 
> as far as I'm concerned, the risk of overheating is counterbalanced by the
> availability of a cold beer.  'course my wife might differ.
> 
> AA
> 
>  
> 
> On Wed, Aug 15, 2012 at 1:59 PM, John Straube <john at buildingscience.com>
> 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 :)
>>  
>>  This all reminds me of the old debate in the first round of low-energy
>> houses.  One crowd wanted to use more and more glass and hence mroe energy
>> collection.  The other said just insulate and reduce energy need.  Now we
>> have a similar scenario.  Following the dogma of PH, everyone wants to use a
>> high (0.6 or more)  SHGC to push to a rather meaningless space-heating
>> target, but in many cases lower (0.5 or less) SHGC will avoid the risks of
>> discomfort due to overheating and provide higher R-values (almost always) at
>> the expense of potentially slightly increased winter space heating energy. 
>> But if you are willing to risk comfort, you can save energy in other ways
>> (e.g. operating the house in winter at a colder temperature). There are lots
>> of examples of comfort problems already, leading to the recommendations of
>> lower SHGC (eg between 0.3 and 0.5 depending on climate) and these will only
>> increases as the houses get better insulated.
>>  
>>  
>>  
>> Dr John Straube, P.Eng.
>>  Building Science Corporation
>>  Westford MA Waterloo ON
>>  
>>  www.BuildingScience.com <http://www.BuildingScience.com>
>>  On 12-08-15 1:14 PM, Alan Abrams wrote:
>>  
>>  
>>> first, the use of exterior shading.  southern exposures in moderate
>>> latitudes only require a 18"-24" overhang to fully protect a 5'-6' window in
>>> early summer, and allow full sun in the dead of winter.  E-W windows are
>>> almost impossible to control with overhangs--but can be inexpensively and
>>> effectively controlled with Interactive Shading Devices (aka shutters).
>>  
>>  
> 
> 
> 
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