Posted by: "MotherLodeBeth" MotherLodeBeth@...
> Nice thing about small houses on wheels is you can move
> them around so the windows in winter get the solar heat and
> light from the south and west sides.
West facing windows are not a good choice for the heating
season. For instance, using Topeka, Kansas (center of the
nation) as an example, during January the net Solar gain
(gain minus heat loss) for an unshaded, double glazed,
clear glass, South facing window will be about 296BTU
per ft², per day. For the same window, facing West, there
will be a 264BTU/ft²-day heat loss. During the "shoulder
months" when West facing windows get more sunlight,
temperatures are warmer and only having South facing
windows still does better. Even in March (sun path the
same as late September) South facing windows still get
38% more sunlight than West, while their heat loss is
the same. So, even in March, West facing windows
gain little heat. In February, they lose 91BTU/ft²-day,
while South facing windows gain 339. The December
West window heat loss is 259, while the South window
gain is 251. For November, West loses 37, and South
gains 443. March, West 171 gain, South 381 gain.
Even October, West 391 gain, South 691 gain. Also
note that this comparison is based on equal heat loss,
while the real world circumstance is that West facing
windows generally have far more heat loss, because
they are exposed to the predominant heating season
winds, and there is a strong warm sheltering in the
areas along South walls of houses. There is also a
factor of sunlight reflection, that is not part of these
calculation. It further reduces the West windows
Solar gain, in Winter.
Then, during the cooling season, West facing windows
cause awful overheating, while South facing windows
have not only the advantage of easy shading, but also
simply receive far less light, even if not shaded, at all,
and what does reach the glass, is greatly reflected off.
For instance, In July while a West facing window will
gain 860BTU/ft²-day, a totally unshaded South facing
window will gain only 500, and shading in July is easy.
A shaded South facing window get only 350 at most
> Yet come summer turn the house so the side with
> the most windows are facing north and west so
> the place stays cooler.
Let's first look at your North facing window idea.
It is easy to understand why you could think that might
be a good idea. In July (using Topeka again, since
it is "average" for the US) while a shaded South facing
window can gain 350BTU per ft² per day, North facing
windows are not shaded by overhangs, and unshaded
North facing windows will gain 390BTU/ft²-day, which
is 11½% more July Solar heat gain, than a South facing
window. So, unfortunately, that idea does not work,
without "wingwalls" or other vertical shading, which
in this case, would destroy the Winter performance.
(and would have other faults)
West facing windows, in Summer, can be virtually
hellish. In July, they are also very difficult to shade, and
we are looking at a heat gain of 860BTU/ft²-day. That
is something you definitely want to avoid. So, the idea
of turning a tiny house to face its greatest window area
any direction other than South, during July (or June, or
August) will cause the house to be hotter (considering
standard overhangs, or comparable provisions). Facing
the window West in Summer will cause severe overheating.
BTW....this is based on NREL climate data. Results
will be similar for all Northern Hemisphere locations..
(Reverse North and South for Southern Hemisphere)
While East facing windows have an advantage, during
shoulder months, of early morning Solar gain, to take
the chill off, their net Solar gain is very close to that of
West facing windows. Therefore, their lack of Winter
Solar gain, and also their undesirable Summer Solar
gain, are about the same as for West facing windows.
Natural Solar Building Design and
Solar Heating/Natural Cooling/Energy
Efficiency Consultation Since 1975
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