Free heat

[rebecca100]

I like the idea of adjustable panels that can be shut when not in use. I have several 4x8 panels of thick green tinted glass that alone during the winter in the sun get really warm when they're stacked together. I could use one of them, but I don't have anything yet to use for the cans....

 

[Marianne]

For those without cans, black metal window screen (2 layers, spaced a bit apart) beat out the cans in a test that builditsolar did:

http://builditsolar.com/Experimental/AirColTesting/Index.htm

Great project, lighthawk!

 

[Joel_BC]

For those without cans, black metal window screen (2 layers, spaced a bit apart) beat out the cans in a test that builditsolar did:

http://builditsolar.com/Experimental/AirColTesting/Index.htm

Great project, lighthawk!

Thanks for the link, Marianne. Very interesting about the screen design.

For those who want to cut to the chase and look at the quite detailed DIY instructions on how to make a solar-heat collector like this, here's the link:
http://builditsolar.com/Experimental/AirColTesting/ScreenCollector/Building.htm

 

[sunsaver]

I'm glad to see y'all checking out Builditsolar.Com. I have told many people about that site. It has a wealth of solar projects and free plans. I used their thermosiphon plan to help me design my solar water heater.

 

[Joel_BC]

I've got a sunheated greenhouse with an 8 x 12ft floor area... pretty small. It gives us about a month extension, both in the early spring and late fall, to the growing season we'd have for lettuce and other leafies. (In between those seasons, we grow tomatoes and peppers in it.) In the 'shoulder seasons' we put remay cloth over the beds at night, and we're able to keep the leafies alive. Even though temps inside the GH will go slightly below freezing.

I'd like to invest a bit of money and time to extend the fall/early-winter season even more without the ongoing expense of supplemental heat. Of course, we get sub-freezing nights, and during the month or so I'd hope to extend our season in, the outdoor temp can get down to -12 or so (Celsius), and sometimes not above freezing during the day.

I'm at about 50* latitude. The optimum sun angle for December is given (by my online calculator) as 16* - 16* off vertical.

So, I know that much. Now I'm wondering whether a solar-heat unit like these ones (cans or screens) can hope to provide enough extra warmth by the end of the day to keep the temps near or just under freezing at night.

I'm supposing, too, that some kind of special thermal mass (something cheap and easy, I'd hope) might be a good idea. The only thermal mass in there now, to speak of, are the foot-deep beds of soil.


Any thoughts?

 

[lighthawk]

This is right off the top of my head. With that in mind... Why couldn't you create a "closed" radiator style pipe system (Black PVC comes to mind) sandwiched between the south facing glass and a black screen absorbing heat from the sun all day. It could be plumbed to run along the floor and heat the floor along with the inside air. It would also retain heat longer into the night as it would act as its own heat sink.
I know this type of system is used in outdoor wood burners to transfer heat to the homes interior.
Just thinking out loud.

 

[Joel_BC]

This is right off the top of my head. With that in mind... Why couldn't you create a "closed" radiator style pipe system (Black PVC comes to mind) sandwiched between the south facing glass and a black screen absorbing heat from the sun all day. It could be plumbed to run along the floor and heat the floor along with the inside air. It would also retain heat longer into the night as it would act as its own heat sink.
I know this type of system is used in outdoor wood burners to transfer heat to the homes interior.
Just thinking out loud.

I guess you're thinking of some kind of anti-freeze (or non-freezing) fluid? Pure water would seem to be an obvious no-no, since it might freeze at night.

And are you thinking of incorporating a commercially made radiator?

At least as far as I can visualize it, the heat generated in the system you're describing would be quite a bit less than that put out by an outdoor wood burner system (a neighbor of ours has one of those, and has heated his home and a small woodworking shop with it). So would a south-end sun-heated, fluid-circulating radiator actually put out enough? And would it work without an electrically-powered pump?

 

[lighthawk]

I guess you're thinking of some kind of anti-freeze (or non-freezing) fluid? Pure water would seem to be an obvious no-no, since it might freeze at night.
And are you thinking of incorporating a commercially made radiator?

At least as far as I can visualize it, the heat generated in the system you're describing would be quite a bit less than that put out by an outdoor wood burner system (a neighbor of ours has one of those, and has heated his home and a small woodworking shop with it). So would a south-end sun-heated, fluid-circulating radiator actually put out enough? And would it work without an electrically-powered pump?

Definately anti-freeze.
Not an actual radiator... Imagine the black pipe running the length of the wall horizontally then elbow 180 degrees up an inch or so to another section of pipe running the length of the wall horizontally back the other way just above it then up to another and so on. Covering the entire wall would block the sun and shade your plants so you might only want to go half way up the wall in this fashion. When finished it might resemble a radiator. At the top the pipe would then go back down to the floor and run along the floor around the perimiter of the green house and back to the "radiator" type collector at the starting point.
It seems to me that as the sun heats the liquid inside the pipe the hot liquid would rise and be forced into the pipe that surrounds the floor forcing cool liquid back into the radiator from the bottom.
The heat generated would be much less that that from a stove hence the black PVC also much lower pressure but higher volume. Whether it would put out enough? Maybe only slightly better than nuthin'? You would need to run it by someone with much more engineering knowledge than me.
I don't think a pump would be needed.
Perhaps a small prototype in a south facing window would be enough to find out if the theory is sound?

 

[Joel_BC]

Definately anti-freeze.
Not an actual radiator... Imagine the black pipe running the length of the wall horizontally then elbow 180 degrees up an inch or so to another section of pipe running the length of the wall horizontally back the other way just above it then up to another and so on. Covering the entire wall would block the sun and shade your plants so you might only want to go half way up the wall in this fashion. When finished it might resemble a radiator. At the top the pipe would then go back down to the floor and run along the floor around the perimiter of the green house and back to the "radiator" type collector at the starting point.
It seems to me that as the sun heats the liquid inside the pipe the hot liquid would rise and be forced into the pipe that surrounds the floor forcing cool liquid back into the radiator from the bottom.
The heat generated would be much less that that from a stove hence the black PVC also much lower pressure but higher volume. Whether it would put out enough? Maybe only slightly better than nuthin'? You would need to run it by someone with much more engineering knowledge than me.
I don't think a pump would be needed.
Perhaps a small prototype in a south facing window would be enough to find out if the theory is sound?

Okay, I can visualize what you have in mind. Yes there might be motion within the pipes... liquid moving, as you suggest. But also seems like there would be an expansion in the liquid as it warms up. So I'd think that some sort of pressure relief might be needed in the system, to keep pipes from bursting... not from freezing, but due to the heat

But just to frame the context a bit better... Our conditions, weather-wise, in November and December, and again in March, are very similar to Boulder, Colorado. But while Boulder has a mid-winter solar angle of 26* (ideal placement of face of panel: 26* off vertical), ours is only 16*. The sun angle is quite low because of how far north we are, and the daily sun arc is small due both to how far south the sun appears and also to the mountain ridges to the east and west. Shortish exposure to sunlight.

 

[lighthawk]

Likewise. Although I have a much steeper sun angle (not sure exactly what it is) I live under a "perma cloud" created by the warm waters of lake michigan. You can't generate heat from the sun if you never see the sun. None the less the panels I installed were a "one time" expense and so every time the sun does shine I reap the benefits free. No matter how small.
I doubt it would generate enough pressure to create a problem except in mid summer although a relief valve would be a good idea even if only to purge the system of trapped air.
There is no way I would suggest the expense of building such a pipe system to try to heat your greenhouse through the winter but in the spring or fall it may extend your growing season even if only for a short time. You said the greenhouse itself extends your season a month on both ends if this system only got you an extra week beyond that would it be worth the time and expense? Only you can answer that.

I'm glad we had this conversation because I do see a small greenhouse in my future and I may incorporate something similar in the planning stages. Perhaps in conjunction with, or additional to, a soda can heater.
Things that make you go Hmmmm.