heat day one

realolman

I know a bit about heat being molecules moving around.

What exactly IS heat and why does insulation keep it in?

what happens to heat if the insulation is extremely thick with gigantic R ratings?

I know these are kind of silly questions, but if anyone would care to answer , I'd be interested in reading it

Jamie Hall

hoo boy...

Now THERE is a topic!  Some folks spend their entire lives on the study of heat -- it's called thermodynamics.  And it can get very exotic, to put it mildly...



But basically, heat is a form of energy.  Except in nuclear reactions, energy is conserved -- that is, it can be transformed from one kind of energy to another, but you can't get rid of it, nor can you create it from nothing.  So we can happily create heat from burning oil -- changing the chemical energy in oil to thermal energy in the flame.  Or we can change mechanical energy into heat (feel your drill after going through the wall of a pipe!).  Or we can change heat into mechanical energy -- a steam engine, for instance.  And so on.  The temperature of a substance gets in here; it, plus the phase (solid, liquid, water), is a measure of the internal energy of a mass of substance -- steam, iron, water, air, whatever.  Temperature is related to how fast the molecules are bouncing around.  If we add heat to a mass of substance -- say the water in a boiler -- the molecules bounce around faster as the temperature rises.  At some point, the molecules are bouncing around so fast that they boil -- break loose of the other molecules of water and go sailing off into space -- instead of going faster.  So the temperature doesn't rise any more as the added energy goes into breaking the bonds rather than making things move faster, but we get steam instead.



Heat can only be transferred from one substance to another with a lower temperature -- you can't go the other way.  It can be transferred by radiation or conduction (which, if the substance transferred to is a liquid or gas, can give rise to convective heat transfer, which is a little different).  So in our boiler, for instance, we have a hot flame, which transfers heat by both radiation and conduction to the iron of the boiler, which is cooler, which transfers heat mostly by conduction to the water, which is cooler still.  Then the steam is nice and hot and is moved to a radiator somewhere, which is cooler, and so the steam condenses (the molecules are slowed enough so that they stick together as liquid water) and the heat transfers to the radiator... which then transfers heat by conduction to the air in the room, which circulates (convection) and makes Grandpa feel warm.



Some substances conduct heat a lot better than others.  Those which are poor conductors are called insulators.  The rate of heat transfer depends on how good the conductor is, how much of it there is, and the temperature difference.  So for your insulated pipes, less heat is transferred out of the pipe to the basement (and more gets to the radiators!).  The heat isn't lost -- it just doesn't leak away as fast.



There are three fundamental laws of thermodynamics.  The first law is "you can't win" -- you can't get more energy out of a closed system than you put into it (although you can change its form).  The second is "you can't even break even at the game" -- the efficiency of any closed system cannot exceed 100% (this is where the perpetual motion boys fall down).  The third is considerably more esoteric, and has to do more with order (called entropy) than heat, but basically it says that if you do something to increase the orderliness of part of a closed system, somewhere else in the closed system becomes much messier.



Not sure that that helps any...

realolman

thanks.. very nice

so I suppose it is impossible to have a container that is so well insulated that it will lose no heat... if it were possible, seems to me the molecules couldn't vibrate around forever....... what would happen   ?



...if they could vibrate for at least for a couple months,  you could let some August heat out in your house in January.

The mechanical energy that heats up your hand when you grab the chuck of your turning drill is turned into what as things cool down?

Mike Kusiak_2

Insulation

If your theoretical container really was insulated perfectly, then the heat energy contained in the mass inside would remain constant and the molecules would essentially vibrate at the same rate forever. The temperature inside would remain constant.



Your comment about storing summer heat for winter use is not too far off. People have installed thermal mass storage systems under their homes to do exactly that. How well they actually work and their cost effectiveness is another matter. One of my relatives actually built something like this by burying a 1000 gal well insulated tank in his back yard to store solar heated water in summer and fall, then retreiving the heat during the heating season. (Also had a 10 KW wind generator in his yard, and his was all 40 years ago. He was well ahead of his time)



You really can store heat, or the lack of it for long periods. Before mechanical refrigeration, large blocks of ice were cut from lakes in winter and kept in insulated underground storage facilities for use through the summer and fall.



As far as your drill, the heat generated by the friction of your hand on the drill chuck is just transferred to the environment by conduction to your hand and by radiation and convection to the air and surroundings. Its release just raises the temperature of the immediate environment by an infinitesimal amount.

Brad White

Pretty much sums that up, Jamie.

Good explanation overall and one of the better ones on entropy.



I understand entropy. I have two cats. THEY understand entropy.

realolman

thermal mass

I guess the thermal tank holding collected summer sun heat is kinda what geothermal is doing.

I suppose there is some method of figuring out how much surface area of pipe you need in contct with the earth to heat a house??

jp_2

100 ft of insulation

even with 100ft of insulation the heat would still migrate though the material.



our plant could be considered perfectly insulated since its surrounded by vacuum thousands of miles thick.   but if we were perfectly insulated the sun would continue to heat the earth til it was the same temp as the sun.



my question is: what happens if you take away ALL heat, is there a point were electrons fall from the atom like apples out of a tree?

Charlie from wmass

Letting out August heat in January

Is just what they did with this house in Virginia. http://bysolar.net/news/Stets_McCleskey_Sweet_SolarToday.pdf

bob_46

Heat

Realolman, be careful what you believe ! Remember what day it was when Jamie and Brad replied to your question. I would ask them to explain an invisible substance called

Caloric and how it behaves. bob

LarryC

The moon is not as hot as the sun.

our plant could be considered perfectly insulated since its surrounded by vacuum thousands of miles thick.   but if we were perfectly insulated the sun would continue to heat the earth til it was the same temp as the sun.



Actually, the Earth radiates solar energy back out into space.  Take the moon, it is not the temperature of the sun even though it is "insulated" with 1000's of miles of vacuum.  One of the reasons the Earth is not as cold as the moon is because our atmosphere traps heat.



my question is: what happens if you take away ALL heat, is there a point were electrons fall from the atom like apples out of a tree?

That point is called absolute zero.  At that temperature, ALL molecular vibration stops and everything just stops moving.  Down in the sub atomic region, regular physics don't apply.  No gravity to speak of.  You can't get colder than absolute zero.  (That's why it is called absolute.)   

realolman

that's very interesting

I'm kinda disappointed that they didn't have any documentation of the actual operation of the system.

I wonder how the actual operation fit the model?

Also, I wonder how raising the temperature from 68 to 72 would affect the % of heat supplemented by  the heatstore. 68 deg. is probably about 14 degrees above the temperature of the earth.

Additionally, the majority of the heat gain is expected between March and September... a period during which I expect there would be little need for heat at all in Virginia, sort of losing the entire point of the heatstore.

It's hard for me to imagine that the heatstore would actually hold the heat for a length of time necessary to provide 70+% for the heating season.