Solar water heating system..

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That could work well with a light-colored curtain that reflects shortwave sun back out of the window, which blocks radiation longer than 3 microns, but an outdoor shade can work better. If a dark-colored curtain converts shortwave sun to longwave heat (eg 10 microns at 80 F), the window won't pass it back to the outdoors. The heat will stay trapped inside the house. This is the original "greenhouse effect."
Nick
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wrote:

Oh for goodness' sake!
I've said that the system I use works. When we bought the curtains we didn't ask the salesman about the physical properties of the fabric!
We don't use any kind of curtains in our greenhouse by the way, that works well too, it doesn't get too hot because of effective and automatic ventilation.
We protect the interior of the car from the greenhouse effect by a plastic sheet over the windscreen when the car is parked in our (south facing) drive. That works too, perhaps you'll be pointing out that it can't.
I know our situation, you don't.
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It's mainly a matter of color. Sounds like it's light-colored.
Nick
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wrote:

LOL!
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wrote:

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Mary Fisher wrote:

If it's "immediate", then the only thing you're registering is the fact that sunlight is no longer hitting _you_. Which is absolutely true. When you block sun from actually hitting your windows, obviously the only heat that can enter is from the thermal gradient if it's warmer outside than in.
If you allow the light to come through the window, then stop it, _something_ inside has to warm up. Light coloured curtains will certainly reflect a significant amount of the light back outside, but some _has_ to become heat, inside the house. If it isn't apparently heating the room as a whole, it's your curtains. When that happens, they'll radiate the heat and probably half of it will end up back outside - but you still end up with more heat inside the house than you would if the light hadn't penetrated the window in the first place. This is why i said "potentially" - if your home is well designed (or in rainy England :-) ), that may not be too much heat.

Preferably aluminium or reflective mylar - though that might really annoy your neighbours!

They deliberately function as a fan to pull warm air out of the hive, and I expect they simply stop doing that as soon as the air they're moving no longer feels too warm, but that's not the same thing as using the curtain - because the stone kept the sun from ever touching the hive. It's the difference between putting shutters in front of your windows and curtains behind them.
--
derek

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That's right. The radiant heat doesn't heat us.

You don't know bees as I do.
Mary
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Mary Fisher wrote:

I may, but that's hardly relevant to the physics behind trapping heat inside your house.
--
derek

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But you said, "They deliberately function as a fan to pull warm air out of the hive, and I expect they simply stop doing that as soon as the air they're moving no longer feels too warm, ... "
I'd said, "on a very hot day the bees in a hive in full sun were flying in a cloud at the front of the hive." not that they were fanning at the entrance.
Mary

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Mary Fisher wrote:

I wasn't there :-). It sounded like that's what you were describing.
--
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I described what was happening, there was no ambiguity.

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What do you mean? Some of my best friends are bees.
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No it doesnt when you calculate the eaves properly.

Those are inside, so the heat still gets in.
And you have to fart around adjusting them daily too.
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I can picture the angles of incidence of the sun varying from winter to summer. I have a covered walkway where I marked "north" by noting the shadow of the support posts at solar noon on a winter day. The sun never shines on that spot in the summertime.
How does one determine the desired eave overhang and angle? I would imagine that different times of day could be selected for the shade needed. Enough shade to shield the house between 10am and 3pm? On June 10th? Those calculations I could make, with input from http://www.gcstudio.com/suncalc.html
I have the same question about my Solar Sponge. It will be fixed to the azimuth of one wall, but I can set it at any elevation that I like. Presuming that it would be most useful before noon, I was going to use suncalc over a 9am-noon period and locate the lowest average variation from sun angle for some fixed panel angle. http://solarsponge.com
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Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
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The max sun elevation at noon on 12 and 6/21 is 90-lat+/-23.5 degrees, eg 26.5 and 73.5 for Phila's 40 N latitude. You might use simple geometry to make an overhang that admits all winter sun on 12/21 and excludes all summer sun at noon on 6/21, with some blank wall between the top of the glass and the overhang. With more effort, you can make an overhang with a triangular cross section that's reflective beneath and bounces more winter sun into the window and still excludes all sun at noon on 12/21.
Nick
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In alt.solar.thermal snipped-for-privacy@ece.villanova.edu wrote:

My stubby little overhang shades the wall completely at noon today. That doesn't seem sufficient. It actually looks like that might have been the design, as the shadow is at the base of the wall at 1pm PDT. That leaves a lot of wall exposed to the afternoon sun.
Maybe I'd rather have an overhang for the 3pm sun.
http://www.eere.energy.gov/consumer/your_home/designing_remodeling/index.cfm/mytopic280 says window sill on June 21 noon for my Moderate climate.
The Australian sites have more overhang, indicating 30% of window height as an overhang, but I think that is at a latitude of 27.
Maybe a pergola, with winter-solstice angle on the boards.
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Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
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snipped-for-privacy@XReXXSolar.usenet.us.com wrote

http://www.eere.energy.gov/consumer/your_home/designing_remodeling/index.cfm/mytopic280
Nope in the mid 30s latitude.

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Australia stretchs from -12 to -38. Maybe you are in the mid-30's.
I was referring to the site http://www.greenhouse.gov.au/yourhome/technical/fs19.htm "For latitudes north of 27.50S the response varies with climate."
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snipped-for-privacy@XReXXSolar.usenet.us.com wrote

Yes, but the bulk of the population actually lives in the mid 30s.

Thats a different issue to what was being discussed, whether its feasible to have an eaves that ensures that no sun enters the house in summer, but does fine in winter.
You dont really need much solar heating at 27S except in the inland and there arent many people living there at all.
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snipped-for-privacy@XReXXSolar.usenet.us.com wrote

I just used a properly sun angle calculator.
That was in the late 60s, bound to be plenty online now.

All you really need to do is ensure that the sun doesnt enter the doors in summer, and set the eaves overhang to ensure that.

Its a lot simpler with windows/patio doors where you just need to ensure that the sun doesnt enter in summer.
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