[Greenbuilding] Light Shelves

[Lawrence Lile]

My old copy of Mazria's book says that a light shelf, nearly horizontal
but sloped 5 degrees away from the building, and covered with highly
reflective material (foil or shiny metal) works best.  If the shelf is
as long as the window is tall, it can increase the total solar heat gain
by 30%, if the shelf is twice as tall, it can increase it by 60%. These
figures are based on a study of year-long heat gain done on models, not
just on theory.  You'd think the numbers would be more like 200%.
Might also help to be wider than the window, to catch morning and
evening rays.  

Obviously this is a bad idea where the shelf can make glare.  I'm
thinking about clerestory windows, way up there.  

Anything just in front of the window, like an exterior Venetian blind,
isn't going to add any solar heat gain, just redirects what is already
coming in.  This is useful for daylighting, but not for my purposes.  

Playing around with angles in AutoCad produced the same result - a 5
degree slope away from the building bounces the most light into the
building, and allows for drainage.  

These would have to be moved or folded up during summer months, or
perhaps attached to the top of the window for deep shade.  In my case,
the solar overhang over the window doesn't do much to stop late
afternoon sun in certain periods of the year.  


 
 
Lawrence Lile, P.E., LEED AP
-----Original Message-----
From: Clarke Olsen [mailto:colsen at taconic.net] 
Sent: Monday, April 30, 2007 1:47 PM
To: Rob Tom
Cc: Lawrence Lile; greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] Light Shelves

>
    This seems like the right approach: a louvered light shelf would 
allow
    rain and wind to pass through. Movable louvers could be tweaked
    indefinitely, perhaps leading back to the getting a life issue....
    Clarke Olsen

> I'm thinking instead of having something like a humongous drawbridge
> affair in front of each window, perhaps the device could be refined to
> take the form of a jalousie ... sort of like exterior Venetian blinds.

> You
> theen ?
>
>
> --