Hybrid Car – More Fun with Less Gas

Increase in collector temps due to snow relection? - Page 2

register ::  Login Password  :: Lost Password?
Posted by SolarFlare on December 10, 2005, 10:47 pm
 
I would think that for a few reasons using logical
deduction.

- when the sun shines the snow melts. Tjhis means it
absorbs much of the thermal energy.
- The solar thermal radiation has to pass through the
glass on a fairly sharp angle when it is high in the
sky (most thermal time of day) and also be reflected
off the snow. If the snow reflects the solar thermal
energy effectively then the glass reflects it
effectively also. I do not know much about transparency
of glass to infrared radiation. I know that light bends
differently than infraded when changing mediums from
infrared photo experience.
- The website Daestrom provided states that reflected
solar radiation is not a factor and need not be
considered. I could find no mention of snow in tables
or text.


is acting like a

all its

get hot to be

only disadvantage

directions.  So to be

have snow spread


Posted by Ecnerwal on December 11, 2005, 5:16 pm
 


Observationally false. When it's moderately cold and the sun shines on a
black-topped driveway, the parts of the driveway which are free of snow,
and thus black, melt off - black ice melts, snow at the edges of the
black patches melts, turns darker, and melts more. The parts of the
driveway which are covered by snow, and thus white, do not melt, other
than inward from the black edges. If most of the snow is removed
(revealing black surface, even if speckled with a bit of snow), the
remainder of the snow melts if the sun is shining. I have extensive
practical knowledge of this behavior from keeping a black-top driveway
in Vermont clear of snow.

Also notably false due to the observed effects upon weather of having,
or not having, a snow-pack in place, which reflects much of the incoming
sun back into space, resulting in less temperature rise for the same sun
input when there is snow in place than when there is not.

I recall that the University of Maine (located in a snowy state) did a
bit of research and determined that vertical collectors work quite well
in Maine, for thermal, due to snow reflection (also lack of snow
building up on the collectors, and they offer simpler/cheaper
construction/mounting by mounting on a vertical house wall).

Time period would be sometime in the 1980's - I'm not finding it online.

--
Cats, coffee, chocolate...vices to live by

Posted by SolarFlare on December 11, 2005, 6:28 pm
 Does this mean only your driveway ever clears away
snow?

Up here in Canada our snow melts off the grass (thermal
absorbant materials) also.

Very strange place that Vermont. Do you have downhill
skiing resorts and slops on the south sides of your
hills too?


in message

the sun shines on a

which are free of snow,

the edges of the

The parts of the

do not melt, other


Posted by Ecnerwal on December 11, 2005, 7:21 pm
 

That's right, snow stays on the grass year round. I don't even own a
lawnmower, I just snowblow the lawn onto the driveway (where it
miraculously melts) a few times a summer to keep the snow at a
convenient height for croquet. We have magical 100% IR reflecting,
perfectly insulating snow here in southern Vermont. Unfortunately our
export laws don't permit sending any to Canada.

In actual point of fact, I don't expect to see any grass other than the
stuff at the edge of the cleared driveway from now until March, barring
a massive, and unusual, thaw. I wouldn't see the driveway for a similar
period if I didn't clear it. You are probably getting dry winds, or
lake/ocean warming if you are seeing your lawn over the course of the
winter.

If you were not immune to facts, you could observe that heat is quite
obviously reflected from snow by placing a dark substance on the surface
of some snow, and leaving other snow untouched, and observe the
differential melting rates, which are directly related to the heat
absorbed. Any heat not absorbed must be reflected. I've been known to
use that effect with wood ashes on sunny days in order to avoid
shoveling or snowblowing long stretches of less critical road (where I
can wait for it to melt off). The treated road will melt in a few days
of good sun - untreated snow pretty much stays put until spring. Nothing
much happens if the sun does not shine.

--
Cats, coffee, chocolate...vices to live by

Posted by SJC on December 11, 2005, 7:44 pm
    It seems to have to do with that .9 albedo number. That would be
.1 absorbed and .9 reflected, even in the IR region. As an observational
data point, I was out in a snow covered area and was using mirrored mylar
for some solar experiments. When I reflected the light off the snow onto the
mirror mylar and onto my face, I got a nice warm face. The IR was indeed
coming off the snow, off the mylar and onto my face with enough heat to
make the 32F seem like 100F.



That's right, snow stays on the grass year round. I don't even own a
lawnmower, I just snowblow the lawn onto the driveway (where it
miraculously melts) a few times a summer to keep the snow at a
convenient height for croquet. We have magical 100% IR reflecting,
perfectly insulating snow here in southern Vermont. Unfortunately our
export laws don't permit sending any to Canada.

In actual point of fact, I don't expect to see any grass other than the
stuff at the edge of the cleared driveway from now until March, barring
a massive, and unusual, thaw. I wouldn't see the driveway for a similar
period if I didn't clear it. You are probably getting dry winds, or
lake/ocean warming if you are seeing your lawn over the course of the
winter.

If you were not immune to facts, you could observe that heat is quite
obviously reflected from snow by placing a dark substance on the surface
of some snow, and leaving other snow untouched, and observe the
differential melting rates, which are directly related to the heat
absorbed. Any heat not absorbed must be reflected. I've been known to
use that effect with wood ashes on sunny days in order to avoid
shoveling or snowblowing long stretches of less critical road (where I
can wait for it to melt off). The treated road will melt in a few days
of good sun - untreated snow pretty much stays put until spring. Nothing
much happens if the sun does not shine.

--
Cats, coffee, chocolate...vices to live by

This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread