Cohousing-L Mailing List: efficiency and tropic climate

[Ellen Franconi (emfbca]

It's great to see the that groups like Broward Commons
are thinking about energy efficiency from all angles. 
I read through the wish list Chris posted and have some
additional ideas that may help create an efficient design.

Creating shading to decrease cooling is a great idea. 
Chris mentioned they were thinking to do this using foliage.
In addition, the indoors can stay cooler if the outside surfaces
are painted white, especially the roof which if not shaded by
trees can really absorb the sun's energy. A study by Lawrence
Berkeley Lab (where I am a researcher in Building Energy) did
some testing on the effectiveness of white roofs in Sacramento,
CA. The results showed the yearly cooling load was reduced 70% for a
one-story, 1800 ft2 house!

Incorporating mass into a design is a real good idea in hot and
dry climates but less critical for hot & humid climates. Hot
&dry climates tend to cool off a lot at night. Thus the mass
will keep the house cool during the day. At night, the mass
cools down if the occupants open the windows and let the night
circulate. The outside surfaces tend to cool down too because
the very clear night sky promotes radiate heat loss.
In a hot & humid climate, it is harder to cool down the mass
at night because temperatures don't fall as low and the sky tends
to be more overcast. If the mass doens't cool down, it will
carry the heat into the next day and make for less comfortable
conditions.  It is good to try to capture the breeze as much
as possible in hot & humid climates and select materials that
"breathe". Vernacular designs include raised floors which
helps cool the surface. 

Of course if you must cool most of the
year, then isolating yourself from the outside environment
is an effective strategy. But you might not want to do
it to such an extent that you can't take advantage of the
comfortable times of the year when natural ventilation would
be sufficient. The insulation levels for cooling need not be
as high as those recommended for cold, heating climates because the
inside-outside temperature difference is much less.  

Hope this helps some. I did get a chance to write a general
article for Cohousing Journal. It looks like it may make it
into the next issue. Unfortunately it is a bit brief 
considering the wide array of issues/topics/resources that
exist. Thanks to everyone who responded with enthusiasm and
suggestions.

-Ellen