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greenhouse First 80 Plants In Greenhouse 02-22-09
- Thread starter AlabamaJack
- Start date
Josh said:
And coastal areas have more moderate daily heat cycles.
Not to get all geeky but...
I believe it's the specific heat capacity of the substance that determines how much heat-energy it can absorb and thus emit when cooling off. I think the far right column here will give you a good comparison of various materials, the higher number - the better:
http://en.wikipedia.org/wiki/Specific_heat#Table_of_specific_heat_capacities
(scroll up for explanation, down for "building materials" - but those are different units)
The Engineer will be along soon to give us all a physics refresher, I hope.
caroltlw said:And coastal areas have more moderate daily heat cycles.
Not to get all geeky but...
I believe it's the specific heat capacity of the substance that determines how much heat-energy it can absorb and thus emit when cooling off. I think the far right column here will give you a good comparison of various materials, the higher number - the better:
http://en.wikipedia.org/wiki/Specific_heat#Table_of_specific_heat_capacities
(scroll up for explanation, down for "building materials" - but those are different units)
The Engineer will be along soon to give us all a physics refresher, I hope.
Carol I have to be honest all that math is intimidating. Where is that engineer when you need him. I need a nice summary of that wiki article.
Thermal mass, thermal inertia, and specific heat capacity- they are your friends!
As for sand versus water- water is about the best thermal mass you can come across and a far better thermal mass than sand- I think where sand comes into this would be where you would be using a sand-filled barrel as a heat exchanger with something like a trash barrel. In my greenhouse, I fill three 60 gallon plastic trashcans with water (after I place them where I want 'em, because they won't move after that!).
I've been toying with the idea of building a solar collector out of old auto radiators, garden hoses, and old single pane windows this spring along these lines- if you build correctly and set up a simple thermosiphon, not only will you have a LOT of thermal mass to help out, you will actually create even more heat rather than just the passive radiant heat the thermal mass will gather up throughout the day.
Not that all this would really be of much help down there where it's a bajillion degrees, or anything
As for sand versus water- water is about the best thermal mass you can come across and a far better thermal mass than sand- I think where sand comes into this would be where you would be using a sand-filled barrel as a heat exchanger with something like a trash barrel. In my greenhouse, I fill three 60 gallon plastic trashcans with water (after I place them where I want 'em, because they won't move after that!).
I've been toying with the idea of building a solar collector out of old auto radiators, garden hoses, and old single pane windows this spring along these lines- if you build correctly and set up a simple thermosiphon, not only will you have a LOT of thermal mass to help out, you will actually create even more heat rather than just the passive radiant heat the thermal mass will gather up throughout the day.
Not that all this would really be of much help down there where it's a bajillion degrees, or anything
AlabamaJack
eXtreme
I like the way you think and talk Hinky...
but if you have the same volume of sand as water and the sand is the same temperature as the water, the sand holds more thermal energy than the water...the thermal mass for the water is less than that of the sand since the sand is heavier per volume than the water....therefore....the sand will hold its heat longer (and will take more energy to heat up) than the water will simply because the density of the sand is higher than the water....and because the water is less dense than the sand, the water will heat up at a higher rate than the sand....
isn't this sound logic? or am i too drunk to reason logically?
but if you have the same volume of sand as water and the sand is the same temperature as the water, the sand holds more thermal energy than the water...the thermal mass for the water is less than that of the sand since the sand is heavier per volume than the water....therefore....the sand will hold its heat longer (and will take more energy to heat up) than the water will simply because the density of the sand is higher than the water....and because the water is less dense than the sand, the water will heat up at a higher rate than the sand....
isn't this sound logic? or am i too drunk to reason logically?
AlabamaJack said:
That's where the specific heat capacity of the material comes into play. If you will notice in the chart referenced above, water has a greater volumetric specific heat than aluminum or copper, though both are denser than water. It's all about molecular structure, though it's usually closely related to density.
Water rules!
AlabamaJack
eXtreme
boy, I must have been drunk last night...and too hung over this morning to even think about it...
Here's the plans for the solar greenhouse that I dream of building some day.
http://survivalplus.com/foods/page0009.htm
Here's what they say about it:
"Why do we rely so heavily on water? It is admittedly hard to work with because it tends to corrode containers and to leak. But water is about the best heat-storing material known and is cheap. The best alternative is rock (in any form from sand through concrete), but water holds about five times more heat. So water reservoirs on walls make compact heat storage that gets a good share of direct incoming sunlight."
http://survivalplus.com/foods/page0009.htm
Here's what they say about it:
"Why do we rely so heavily on water? It is admittedly hard to work with because it tends to corrode containers and to leak. But water is about the best heat-storing material known and is cheap. The best alternative is rock (in any form from sand through concrete), but water holds about five times more heat. So water reservoirs on walls make compact heat storage that gets a good share of direct incoming sunlight."
AlabamaJack
eXtreme
I remember that...it would be extremely nice to have one of those...I wish you luck in getting it built Pam...as I recall, this the most efficient greenhouse design there is...and I forgot that about the water...
AlabamaJack said:
Yeah, I had forgotten what they said about water, too. Every now and then I get that out and read it, though. Someday...
Josh said:
Well, therein lies the shortcoming of all solar systems, doesn't it? It wouldn't stop me from building my dream solar greenhouse, mind you, or from adding a solar system of some sort to the house; but right now there really isn't any way to go totally solar unless you're prepared to do without once in a while.
I like the attention to insulation and conserving the sun's energy in this plan. Since it's been published, there have been some improvements in materials, too. When my ship finally comes in, I might be able to make it even more efficient.
AlabamaJack
eXtreme
in the mid-70s I sat down and drew up some plans for my Dreamhouse....
it was a 2 story with the whole southside a greenhouse...the house was going to be 60 feet long and 30 feet wide. drew up the plans and they are stashed somewhere in my attic....here is a crude representation of what I was planning...I was going to use the heat produced in the wintertime to heat the house...summertime was another story...
it was a 2 story with the whole southside a greenhouse...the house was going to be 60 feet long and 30 feet wide. drew up the plans and they are stashed somewhere in my attic....here is a crude representation of what I was planning...I was going to use the heat produced in the wintertime to heat the house...summertime was another story...
AlabamaJack said:
That's cool!
This is the discussion I have with a lot of people who want and design green homes. I could mostly heat my house in the winter using current solar technologies, but what is equally important is cooling in the summer. Well, that and a way to prevent the same structures that allow the winter heating from adding heat in the summer.
One solution that I've actually seen working is to use a passive solar collector that blows heated air into the house in the winter, and in the summer is switched to a solar water heating system.
AlabamaJack
eXtreme
one of the things I was going to do is the House wall connecting the greenhouse was going to be "special" in that it was going to be "overly insulated" to keep the heat out of the house in the summer...
if I had not decided to stay in Texas 10 years ago, that house would be being built as I am typing this...our family owned 130 acres in deep south mississippi (45 miles north of the gulf, Lucedale if anyone knows about the rural areas down there) It had been in the family 150 years...when I told my parents I was not coming back to mississippi, they sold the farm and moved back to Pensacola...I often have mixed emotions about not going back to my roots, especially now that I have gone crazy over gardening...
if I had not decided to stay in Texas 10 years ago, that house would be being built as I am typing this...our family owned 130 acres in deep south mississippi (45 miles north of the gulf, Lucedale if anyone knows about the rural areas down there) It had been in the family 150 years...when I told my parents I was not coming back to mississippi, they sold the farm and moved back to Pensacola...I often have mixed emotions about not going back to my roots, especially now that I have gone crazy over gardening...
One thing that my greenhouse (if I ever get around to building it) will have is a 6'x3' area set aside for composting. The bin will be raised off the ground a bit to allow materials to fall through a screen in the bottom. As my plans are to grow the year around, I would always have material to add to it and besides the nutrient values of the compost, it would also provide a bit of heat.
Mike
Mike
