Emit & Absorb IR

DaveGateway

I was just looking at some physics websites.

Boltzmann Law: BL = 1/4 x C x A,
C is speed of light, A is a radiation constant

roughly, radiation of IR from a surface = E x BL x (Temp to the 4th power)
E is the emittance of the surface (0 to 1.0)
Temp has a great effect!!!

The E of white PEX is pretty good (about .8) the E for copper is pretty low (about .03 to .1 depending on tarnish)

Now comes absorption, I couldn't find any formulas but:
flat black or dark green are pretty good! (about .9)

Sooo, on a PEX between joist job,
I wonder if painting the underside of the subfloor a flat black or dark green would increase the IR transfer enough to make a noticable improvement?
BP

Robert O'Connor_7

What?

You lost me @ Boltzman!!!

Weezbo

it should make for readier absorption:)

clear as a bell. light goes to dark .heat goes to cold. darken the absorber speed the absorption.:)

scrook_2

remember...

that's ABSOLUTE temmperature: add 459° to °F to get °R (Rankine) or add 273° to °C to get K (Kelvin -- note: no degree symbol, just "K")

So that hot water radiator's 639°R (180°F) and that steam rad is 674°R (215°F), 5.5% warmer so emits 24% -- (674/639)^4 -- more heat energy (for the same size/shape/type) not the 19.4% warmer (and NOT emiting 204% more) that you might think at first glance!

scrook_2

Boltzman

figured out that the emmission of energy increases lots faster (as the fourth power in fact) than the temperature increases

Aidan (UK)

> clear as a bell. light goes to dark .heat goes to

> cold. darken the absorber speed the absorption.:)



"I wonder if painting the underside of the subfloor a flat black or dark green would increase the IR transfer enough to make a noticable improvement?

Aidan (UK)

Yes



> job, I wonder if painting the underside of the

> subfloor a flat black or dark green would

> increase the IR transfer enough to make a

> noticable improvement? BP




Yes but, if I've understood you correctly, painting the underside of the subfloor will increase emissivity (& absorption) to & from the ground. It will increase the emission, but I don't know if the difference would be noticeable. One of the UFH companies here offers radiant plates that are painted black.

Mike T., Swampeast MO

Where did you find the emissivity rating of PEX? I've been looking and asking for that...

Copper can be extemely low in emissivity (when highly polished) but also extremely high (approaching .95 or so where 1.0 is "perfect") when naturally blackened with oxidation.

Never, ever forget that emissivity is a two-way value--it is the ability of a substance to both receive AND transmit radiation and at a given radiation wavelength most? all? substances are equally able to do both. Absorptivity is just a measure of the ability to absorb. Reflectivity is the opposite (reciprocal) of emissivity.

Bare tube in a joist bay is an amazingly complex construction when it comes to convection/radiation.

While in theory you can increase radiation by making the underside of the floor as emissive as possible (like by painting flat black) and the rest of the enclosure as reflective as possible (like with foil) there are some real problems.

1) There just isn't much surface area of the tube so radiation is quite limited at usable temperatures.

2) The real limitation on the ability to get heat out of a bare tube system seems to be the amount of heat that can be conducted from the water through to the outer surface of the tube. If you take measures to increase radiation, convection slows and vice versa. The only thing that changes appreciably is the speed at which the heat is transferred from the outer tube wall to the enclosure. Radiation is essentially instant--convection is extremely slow in comparison.

The only way to actually increase the output of the system significantly is via conduction. You have to enhance the ability to get heat out of the outer tube wall.

One way surrounds the tube as much as possible with a good conductor that is in turn physically attached to the radiant panel. This essentially eliminates convection and radiation.

Another way again surrounds the tube as much as possible with a good conductor. But instead of being attached to the panel, there will be perforated "wings" to enhance convection. There is still some radiation in this system but not as much as you might think--the convection (air movement) is enhanced to the point that it prevents the "wings" from heating to their full radiative potential.

Both ways work, but IMHO the conductive route is more conducive to responsive control and increased fuel efficiency.

p.s. You can also increase output from a bare tube system by using a tube that is a better conductor to begin with--like copper. Remember that PEX (like most plastics) is a pretty good insulator...

DaveGateway

Emit & Absorb IR

Hello Mike T.

I can't find PEX numbers today?

"Never, ever forget that emissivity is a two-way value--it is the ability of a substance to both receive AND transmit radiation and at a given radiation wavelength most? all? substances are equally able to do both. Absorptivity is just a measure of the ability to absorb. Reflectivity is the opposite (reciprocal) of emissivity."

Emittance & absorption are not always equal or even close!
See: http://www.tak2000.com/data/finish.htm for e/a ratios

White roofs help keep a house cooler in summer! & dark objects get much hotter in the sunshine!

"1) There just isn't much surface area of the tube so radiation is quite limited at usable temperatures."

Is this an opinion or do you have data?

Thanks for any input as I am trying to learn via dialog.
BP

jerry scharf

white bodies and black bodies

There's lots involved, but Mike is right as to the rules. A black body (imaging a hollow sphere with a hole just big enough to let a few photons in and out) is both the highest level of absorption and emission, it defines 1.0. All other objects are more complex, but follow the total energy correlation.

The white roof vs. black roof and it's effect on house temps is a nosequiter. If you take that black shingle, put it in a lab setup with photodetectors and warm it to temp x, the total power radiated will be higher than if you do the same for the white shingle.

There are cases where this is important and places where it's not. I'm not sure there would or wouldn't be an appreciable change in the net output for a staple up application. It's interesting, and I would probably want to do some experimental cells to see. If I can't do it in the lab, I know it won't work in the field. The other way is harder.

jerry

DaveGateway

Emit & Absorb IR

Jerry,

Emittance & absorption are not always equal or even close! See: http://www.tak2000.com/data/finish.htm for e/a ratios

BP

Mike T., Swampeast MO

Check out this link

Absorb & Emit

I'll take a stab at the "white roof" vs "dark roof" thing--corrections appreciated!

The sun is EXTREMELY hot--it emits a full spectrum of radiation from radio (very long waves) through beta particles (entire neutrons). Between these are infrared, visible light, ultraviolet light, x-rays, gamma-rays and alpha particles (electrons). (I probably left some forms of radiation out--sorry am working from memory, not texts.)

While these "waves", "rays" and "particles" may be perceived differently by our senses they really are the same in that they obey the same laws.

I'm sure you've heard the statement that, "You can't get light without heat." Rather strange when you consider that the visible spectrum IS NOT HEAT--IT IS LIGHT! But why can't you get one without the other? Because to get light you have to have heat in the first place and to have heat you have to have an object and if you have an object it radiates heat. The sun is EXTREMELY massive--so it gives off LOTS of heat with its light. A tungston lightbulb filament has a fair amount of mass. When electricity goes through it it heats--it heats so much that it's giving off visible light--but the mass of the filament is also radiating heat at the same time.

A fluorescent tube on the other hand is filled with gas--gas has very little mass. When the gas is excited it gets REALLY hot--there's just so little mass that you can't really measure the temperature without measuring the temperature of the device used to measure! This is where the concept of "color temperature" comes from--it's the temperature required of an object to give off light of a certain character. But again with something like gas in a fluorescent tube you won't be able to "find" anything inside at that temperature. With so little mass in the gas, you're getting a lot of light (because color temperature is so high) but not a lot of heat because there's just not enough mass to radiate much energy in the form of heat...

We can't get an extremely high temperature with a tungsten filament because it would just melt.

Street lights (mercury, sodium, etc.) vaporize things and you can have relatively low temperature (think of the orange hue of a sodium bulb) but you still get lots of light but again, little heat because the mass of the thing creating the light is so low...

Why the stuff about light bulbs? Because that's the best way I know to "see" how emission, temperature, frequency and mass are related when it comes to radiation.

To be continued....

Tim Doran_2

Angle factors

Part of this radiation thing is also angle factors and surface relationships. There is a calculation called the Nessult Theer Calculation that deals with this. I probably spelled it wrong and can not find a copy of it anywhere which is probably good as it is most likely way over my head.

I do know that some of the more progressive engineering firms are looking at this stuff when designing a building with radiant heating or cooling.



Tim D.

Mike T., Swampeast MO

Radiation is a Two-Way Street

This is the part that gets strange, but if you don't understand nothing else will make sense.

ANY object above absolute zero in temperature radiates energy. PERIOD!

In the "real" universe (where absolute zero is only an idea) this means that EVERY object--no matter how small and no matter how cold--is giving off energy to every other object it can "see"--and there is ALWAYS something to "see".

Since EVERY object is giving off energy this also means that EVERY object is RECEIVING energy as well! There is no such thing as total isolation in the universe!

Say you could somehow make a universe of only two completely identical objects at the exact same (non-absolute zero) temperature. Does this mean that there is no energy transferring between them? NO! It just means that they are transferring the EXACT SAME AMOUNT of energy between each other!

To be continued...

Tim Doran_2

yupper

This is how it is possible for two opposed surfaces to render one another neutral. This is also why radiant walls opposed to large area's of glazing may make sense. The steep angles help reduce deflection and increase radiant absorbtion. The angle factor thing. Some also say that this angle thing applies to the relationship of the occupants to the radiant surface. Dr. Olesen also speaks about radiant asymetry which has to do with this relationship and distance from the surface as it relates to comfort. Interesting stuff.

Tim D.

Mike T., Swampeast MO

Why Does an Object Have to Give Off Energy?

GREAT QUESTION! Unfortunately, the "answer" I find published is essentially circular. [GAAK! I originally wrote "circulator"!] An object is giving off energy because it is receiving energy...

So why is it receiving energy? Because it is giving off energy...

HORRIDLY CONFUSING

The following is CONJECTURE!!!!

If we think in broader terms than just "energy", you can say that objects are actually trying to turn each other into their own image and radiation is the way they have to do it...

BUT, again, it's a two-way street and an object is compelled to ALSO try to BECOME the other as well as to TRANSFORM!

Back to that "universe" of two identical objects at identical temperature.

They're emitting and receiving the exact same amount of energy between one another and you would think this would be a perfect balance and that nothing would ever change.

NO! Guess what happens? Both objects cool. But cooling means a loss of energy and if they are radiating the exact amount of energy between one another how is there anything to loose? The objects are identical so they can't turn each other into their image because it is already the same.

Now we get "space". The objects not only want to be identical, they want to be in the exact same space. Little parts of the energy transfer between them hit in perfect phase and cancel each other out but this energy is not lost--it is transformed into a force that pulls the objects closer together...

So what happens when these object meets? Do we get a "universe" made of a giant chunk of stuff at absolute zero in temperature? No. ALL of the matter also wants to occupy the exact same space. For an instant distance becomes "zero" and mass becomes "one" then the universe inverts itself and distance becomes "one" while mass is of any given "object" is "zero". Pure energy that starts rebuilding itself into mass.

To be continued...

p.s. Just like I don't research the design of condensing/modulating boilers, I don't read Sagan or Hawking. I'm sure there are ENORMOUS problems with this theory (and I have simplifed to the EXTREME), but in my head it all fits.

DaveGateway

Emit & Absorb IR

Mike T.
Your theory reminds me of some of my thoughts back in the 60's!
Soooo, can heat transfer efficency be increased by painting the subfloor with an IR absorbing paint?
Kind of like a selective black-chrome solar panel surface?
Did you look at that website with the a/e ratios?
BP

Mike T., Swampeast MO

Was but a true child in the 60s. Have never touched that chemical product of that age but have read stories of the "trips." I kind of do it naturally... Swear that I once actually became part of my heating system and was just a BTU flowing--but I knew where I was going! Sincerely no chemicals involved. My one occasional plant "weakness" is actually kind of a relief as it prevents me from holding a thought and I get a "break" from this crazy mind of mine.

Mike T., Swampeast MO

Not surprising. I still swear that the US Capitol Radiators (thin-fin) with a "tube" made up of four bell curves have unusual radiation characteristics. Can't explain as yet, but things seem "off" when I try to calculate their actual radiative output in a real space...

Polyphase radiation anyone???

Will look into it a bit, but won't make promises regarding "English" explanations. Can deal with high math when I arrived at it on my own, but not when reading equations.

imatellerslie

Bill, Jerry is right, and so are you...

The table you referred us to contains solar absorbtivity and normal emissivity. Emissivity for a surface is a function of the wavelength of radiation that's being absorbed/emitted. The numbers in your table are an average for the predominant wavelengths of the energy from the sun (solar absorbtivity) and an average for infrared (normal emissivity), so you're comparing apples to oranges in that table. The ratio is designed to be a measure of how effective a coating is at keeping a surface cool when it's exposed to the sun, absorbing energy from the sun's radiation and emitting energy in the infrared.

With respect to your particular question about tubes inside a joist bay, I think solar absorbtivity is irrelevant, and thus you shouldn't be using those values. If you're considering how a surface radiates and absorbs infrared energy, then emissivity and absorbtion are the same number.

Thus, the black surface on the underside of the floor will absorb infrared radiation better, but it will emit infrared radiation better too, so nothing gained. In fact, if Mike is right about conduction/convection being the predominant heat transfer mechanism in the joist bay (and I think he is), then higher emissivity of the surface will only help the floor radiate heat back down into the joist bay, which is clearly not desirable.

Mike T., Swampeast MO

""1) There just isn't much surface area of the tube so radiation is quite limited at usable temperatures."

Is this an opinion or do you have data?"

Both.

I once tried to "prove"--well at least come up with a number--that bare tube joist bay systems had a significant amount of radiative output. Particularly when you start trying to take measures to increase the radiation to where you want it like painting the underside of the floor black and making other portions highly reflective.

Failed pretty miserably--particularly when it comes to PEX or similar plastic tube. [Will dig and send you some of the writings--they were written at a private heating forum where "rants" and bizarre ideas are encouraged so be forewarned...]

Anyway there are LOTS of problems, not the least of which is modeling. I have no laboratory besides my house and what I can make--and I'm not about to screw with my "real" heating system just for experiments--it's essentially all black iron including near boiler and running at very low temperature...

A tube running through a rectangle might sound simple--but when it comes to radiant floor heating it's anything but...

1) It leaks air.

2) You really only want heat to go to ONE plane of that rectangle.

3) The available surface of the "radiator" (the tube) is VERY small and incident angles of reflection REALLY matter since less than half of the tube has a view of the floor anyway. While you might be able to model a "perfect" placement and proportions, in reality you're not going to get even close!

4) The available temperature of the radiator is EXTREMELY limited. If you're going to get a lot of radiation out of a small object it has to be HOT! PEX in particular has problems--not only is its emissivity fairly low compared to many common materials, it's VERY limited in temperature.

5) There is that pesky convection lurking everywhere and even if you can model and predict for an ideal construction the air leaks in real construction throw things into the "supercomputer" category.

The only way I could find significant radiation was the "Ken Secor way". Weathered copper tube strapped tightly to the under side of the floor (copper tube straps) run at HIGH temperature (like 200°) under digital control with [preferrably] reflective rigid insulation forming the lower portion of the cavity. He has a system for doing this economically in existing structure, but the learning curve to install such efficiently seems rather steep...

Mike T., Swampeast MO

What is the Nature of the Energy Transferred Between Object?

Another really good question.

[Trust me, I'm working my way to the light roof vs. dark roof goal.]

The most certain thing is that the nature of the emission varies with the temperature of the object that is emitting.

The best and most current "simple" explanation I can find is that it is a massless "bundle" of energy.

If that sounds impossible and confusing to you, you are not alone. Not only is it a single massless thing, but a bundle of massless things that are still without mass!

What is known is that we CAN get a physical "view" of the energy by observing what it does to actual things (with mass) that are around it.

It seems to be a wave--but not a simple wave. It's a wave with two distinct components at 90° opposition to one another.

Sound is similar even though it only has one component.
Sound is easy for us to "see" on an oscilloscope. Just like sound this energy varies in frequency (distance between cycles) and amplitude (height of an individual cycles).

The frequency is determined by the heat of the object and the amplitude by how much energy is being transmitted. The hotter the object the higher the frequency of the emission and the larger? more different? the object the greater the amplitude.

Now you have to consider space. Space is nothingness--an area without matter. As far as we can understand, all of these energy "bundles" move through space at the exact same speed--the speed of light (perhaps better described as the speed of energy since radio, gamma rays and everything in between all obey...) and this speed can ONLY be achieved by "things" that have no mass.

So, what we have is massless bundles or packets of energy that all travel at the same speed between points despite the length of the path [as we "see" by frequency and amplitude] being wildly different!

The last thing that can be said for certain about the nature of this energy is that is the LEAST UNDERSTOOD method of energy transfer. Given the above is there any wonder why?

Since this energy transfer is ALWAYS a two-way street does this mean that the energy going to-and-fro between object is "riding" on the same dual wave in opposite directions or are they distinctly separate dual waves? I'm not sure and don't know if anyone can answer this question. Would truly appreciate any links to CONJECTURE on the subject...

The following is my CONJECTURE.

There's a touch of a problem when energy transfer gets so powerful and energetic that it can be determined to have actual mass... Instead of "radiation" we now call this "radioactivity" yet for one pesky little thing (speed of light) they seem to obey the exact same laws... The nuclear fusion in the sun is producing radiation AND radioactivity as far as I can understand the literature.

What happens to the actual particles and at what speed do they travel through space? When I search the web for such I wind up in terribly complex and theoretical ideas...

The vast majority of the relatively big beta particles (neutrons) would seem to be pulled back into the sun because of their desire to occupy the same space... I can almost see those big arcing solar flares as "hot spots" of beta particles...

But what about the relatively tiny alpha particles (electrons)?

One thing that we know about alpha particles is that they don't travel well through air--just inches.

Another thing we know about alpha particles (electrons) is that there is an incalculable reservoir of free electrons (dare I say alpha particles) in the earth itself. What we don't seem to know (or perhaps don't want to believe) is where these came from...

It seems rather naïve to believe that these free electrons have come from anywhere EXCEPT the sun. But wait--alpha particles can't travel well through air...

Another thing we know is that there is an electron deficit in the upper atmosphere (in other words an over-abundance of positive ions).

Can you say "lightning"?

Can you belive that WITHOUT lightning there would be a hyper-abundance of NEGATIVE ions in the atmosphere?

Can you possibly believe that electricity (in the way we think of it) is nothing more than a forced movement of solar energy?

Could you conceive it possible to mimic the effects of lighting in a completely usable and controlled way? Like perhaps a "gateway" to the upper atmosphere that resonates the earth into the sky and the sky into the earth?

To be continued...

p.s. My New Year's resolution was to understand what Tesla was trying to do with Wardenclyffe and how he intended to do it. This is NOT to say that I could duplicate OR that it would work to begin with.

People seem to have a tendency to ignore the big picture (like interaction of sun with earth) and instead concentrate on the little things that they think they can understand. Then they make the little things so ridiculously complicated that most think the big picture to be beyond possible comprehension.

In my mind, it's EVER much easier to imagine the entire scope of the project in the beginning and then identify how the components become part of the whole.

DaveGateway

Emit & Absorb IR

Mike T.,
I have never heard of Ken Secor, but I did something close.
About 2" under my Great Room subfloor, I put 4 runs of weathered black 1/2" copper per 16" joist space. It slides quietly in plastic bushings. About 12" below that I put in Reflectex, which is a multi-layer aluminized plastic product. It seems to heat the room fine with 120* input & about a 15* delta-T at 0* outside, 2x low head El-sid 24vdc pumps for this zone.
The reason WHY you may ask, I ran out of PEX & had alot of old 20' sticks.
I haven't tried the flat black paint on the bottom of the subfloor. I would like to do some testing.
Bill Patrick

Mike T., Swampeast MO

Where Does this Energy Transfer Occur?

Beyond "between objects" about all we seem to know for certain is that it appears to happen on the surface AND between surfaces that are in a certain type of alignment to one another.

Things as small as molecules (perhaps atoms, perhaps sub-atomic particles, perhaps "quarks") are able to transmit energy between one another in this way.

Gasses really don't have "surfaces"--conseqently much energy passes through the gas without being "caught". The gasses are themselves vibrating so rapidly that only rarely are they in the proper alignment between one another for this energy transfer to occur.

But again, where does this energy transfer occur? Between molecules? Between atoms? Between protons and electrons? Between protons and protons? Between electrons and electrons? Between quarks and electrons? Between neutrons and neutrons? {and so on] Between all, some, similar pairs, opposite pairs? In that regard I can't find an answer--references appreciated.

From what we can "see" though, the energy transfer is occurring between the surfaces of distinct objects in view of one another. Does this mean that every surface both produces and accepts this energy in the same way?

Most certainly no! Objects are better "tuned" to some frequencies of this energy than anothers. Two very different things happen when the objects aren't "tuned". The energy either bounces back (reflects) or it passes through.

Reflection is NOT the same as reception and transmission! Reflection essentially bounces back the energy UNALTERED without the energy becoming part of the reflecting object. In receptions/transmission the energy becomes PART of the object and its character depends on the temperature of the object transmitting. This is where you get the concept of "emissivity". For most practical purposes, an object that receives this energy at a given wavelenth is equally as good at transmitting at this wavelength.

Now go back to that simple "universe" of two identical objects--but now while identical in form they are different in temperature. The hotter object transmits X amount of energy to the cooler object. The cooler object transmits Y (a smaller) amount of energy to the warmer. The cooler object is receiving more energy than it transmits so it warms. The warmer object is transmitting more energy than it receives so it cools. The formulas you will find for computing the net effect of this energy already take the two-way nature into account. The problem though is that such formulas become "undefined" when both objects are at the same temperature and it's easy to think that transmission of energy has stopped--when in fact it is occurring at an equal (but undefined in such equations I believe) amount.

So, does a given substance always have the same values of reflection, transmission and acceptance at a given frequency of energy? Unfortunately no! It varies not only with the physical state of the substance (water/ice/snow is a WONDERFUL example of this) but with nature of the surface of the substance--(again water in the form of ice or snow is a very good example). Extremely smooth and polished surfaces (of the exact same substance) will generally be more reflective and less accepting... EEEK! As soon as you think you find something "simple" in all of this, it gets even more complicated!

The issue of transparency is even more complicated. It doesn't seem to happen in a way that makes sense to our human senses. Low frequency and relatively low intensity emissions like radio waves are able to pass through an amazing amount of substances we consider "solid". They also start bouncing (reflecting) off "things" like clouds and other atmospheric phenomenon which have little mass to begin with!

Towards the other end of the scale you get gamma rays that are incredibly high frequency and generally high intensisty. This energy passes through amazing amounts of substances that we consider solid--the problem is that this energy is of such intensity that it actually starts changing the substance it passes through--and generally it is NOT a change for the "better". The tiny portion of the energy that IS accepted into the object still has so much intensity that it physically changes it by forcing it to RETURN energy at such a level that it is transformed in the process...

To understand just how selective matter can be to this energy we CAN use our senses--particularly the sense of sight.

The visible portion of this energy is EXTREMELY small in comparison to the whole. We "see" different colors based on the ability of substances to REFLECT varying amounts of energy in this TINY portion of the spectrum. We can distinguish literally MILLIONS of different colors with our eyes...

To be continued...

Mike T., Swampeast MO

Does this Energy Remain in the Same Form when Transferred?

NO!

It depends on the temperature of the objects doing the transmission.

And here we actually can "trust" our senses somewhat for "proof."

Put a black roof on a house. "Black" means that the visible portion of the energy spectrum is being absorbed by the surface--extremely little visible light is being reflected.

So, the black roof is absorbing much of the visible light energy in its "view" of the sun. While light is NOT heat is IS energy--and since this black roof is accepting energy in the form of light it MUST give back a portion of this energy. The problem is, that the roof is not hot enough to give it back in the form of light, so what happens? It returns this as infrared energy--what we call "heat". The light received from the sun is quite literally transformed into heat INSIDE the MUCH cooler object! But is all of this heat returned in the form of infrared radiation? NO! Why? Because the roof is a "solid" and has mass. Much of this energy heats the object itself. In other words, the energy received at the SURFACE is "pulled" into the object itself and we have conduction. Only after the interior of the object has heated to some degree can the surface also increase in temperature to allow more energy to be transmitted. (This is how you can "see" the difference between emissivity and reflectivity.)

Remember--the black roof is ALSO receiving infrared (heat) energy from the sun. The light energy is INCREASING it's heat beyond the level of the actual heat energy it receives because heat is the "highest" form of energy it can return...

A white roof on the other hand reflects and scatters much of the energy in the form of light that strike it. This energy never makes it past the surface so it never has to be transformed and returned. The white roof is mainly receiving energy only in the form of "heat" and it won't get as hot as a black roof.

[Sorry to take so long and twisting a road to arrive at an "answer" to a "simple" question. The problem is that an equally "simple" answer does nothing to show "why"?]

To be continued...

Ken_8

There ya go...

Yet another person who never heard of me.

Like Rodney Dangerfield says...

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mike T., Swampeast MO

How is Energy Returned to the Sun?

Since the earth is receiving energy from the sun it MUST be returning some of this energy. We do have a very good idea of the amount of solar energy being received from the sun, so even though I've never seen such, there must be a number somewhere of how much energy the earth is transmitting...

But what form does it take?

Is it primarily infrared? Seems rather unlikely even though the temperature of the planet itself would "say" that this is the ONLY form possible. Why? Because one VERY IMPORTANT function of our atmosphere is to REFLECT infrared radiation back to the surface--the so-called "greenhouse effect". A certain measure of this is REQUIRED for us to exist--like many things in life moderation is fine (often even good) but too much and bad things happen...

And where does it go?

While the overwhelming amount of energy being received by the earth from the universe comes from our sun, that doesn't necessarily mean that the energy it is forced to return must go back directly... The earth has view of MUCH more than just the sun...

The following is SPECULATION.

The upper atmosphere has some really freakish things going on--prime of which are the Van Allen radiation belts.

Originally there was "one" of these, then there were "two", now there are believed to be "three". All have wildly different properties and are made up primarily of different types of sub-atomic particles at different (but VERY high) "general" levels of energy.

Very little seems to be known about what they actually are, but strangely, most agree that they have something to do with the aurora borealis (northern & southern lights). Some speculate that some of the belts are sub-atomic particles received from the sun during its solar "storms." [Interesting huh? Now we even have protons and neutrons coming from the sun?"]

I wonder if they are in fact the "things" that actually transmit the bulk of the energy back to the sun.

In this perpetually two-way street of energy transfer it can get REALLY difficult to separate result from consequence.

Perhaps those radiation belts echo the solar cycle not because of result (reception), but for consequence (transmission).

This makes me wonder if perhaps the aurora borealis are our transmission of energy to objects in the universe OTHER than the sun...

The earth is FAR more magnetic than science has ever been able to explain. Again SPECULATION, but I wonder if the magnetism comes from the DEFICIT of energy being returned directly to the true source--our sun--instead going in surplus to other objects in the universe...

Mass, energy, time, velocity, gravity, magnetism, etc. are all "supposed" to be predictably related to one another. The finest human intellects have only been able to relate a few of these together or "explain" individual elements even though the explanation of any one hinges on others...

Personally, I believe that physicists are "stuck" because of an improper idea--and it ALL has to do with the nature of this thing we call radiation.

DaveGateway

Emit & Absorb IR

imatellerslie, hello

The graphs that I have seen, show that about 1/3 of the heat transfered from the top surface of the floor to a room is via convection, & about 2/3 via IR radiation.

Please evaluate these conditions below a subfloor:
White PEX with a surface temp. of, lets say 170*F
The subfloor above is painted with an IR absorbing flat black, with a surface temp. of, lets say 100*F
Below the PEX is a reflective radiant barrier.

What I see:
The IR will radiate out in all directions from the PEX.
Most of the IR that strikes the reflective radiant barrier will be relected back off of it.
Most of the IR that strikes the black subfloor will be absorbed & then re-emitted, but some of this absorbed energy heats the subfloor.

The bottom line is that IR will transfer heat from the PEX to the subfloor.

The question is: will the IR absorbing black paint increase the rate of transfer?

Thanks Bill Patrick

Mike T., Swampeast MO

Bill, I'm going to rephrase your question a bit...

Will IR absorbing black paint increase the NET heat transfer from the fluid in the tube? Will an increase in IR transfer result in a corresponding decrease in convection?

Mike T., Swampeast MO

What I \"see\" happening...

Regarding a large, low-temperature radiant panel such as a floor, wall, or ceiling:

You have to get the heat from the water, through the tube, into the panel and finally into the space to be heated.

For a given panel construction (including transfer method from the water) at a given temperature there seems to be an "ultimate" surface temperature achievable at the panel.

Nothing shocking there BUT, the actual output FROM the panel to the space varies--sometimes to an amazing degree.

In other words just because you CAN transfer say 3,000 BTUs/hr from the surface of the panel into the space does not mean that you WILL be transferring this number even though the surface temperature of the panel remains unchanged!

The ONLY way I can understand this happening is for that amount of heat that was actually CONDUCTED from the water and ultimately to the emission surface.

Why only conduction? Because conduction doesn't work like radiation and convection--both of these require a "driving force" to work. What driving force? A difference in temperature?

Conduction does not work the same way. Think of an electrical wire. It transmits almost exactly the energy REQUIRED by the load. It is not driven by a difference in temperature, it is driven by a difference in requirement!

If you've put the vast majority of the BTUs from the water into the system via CONDUCTION you CAN AND WILL draw a different amount of "power" from the panel surface that depends on its "load" (i.e. the mean radiant temperature of the space surrounding). While the surface temperature of the panel WON'T change, the amount of energy flowing through it WILL change!

Now stop this conduction from the water to the surface of the panel--say a bare tube system.

In order to change the output from the tube wall you have to change the temperature of the surroundings! It doesn't matter if the heat leaves the tube via radiation or convection--at any given temperature of the panel the transfer to the panel will be the same! To get more heat from the system you have to reduce the temperature of the panel or increase the temperature of the fluid!

In this way bare tube systems are "living on the edge". While you can get a bit of conduction if the tube is held tightly to the panel, it's just not going to be much. This type of system CANNOT respond well to changes in mean radiant temperature! Why? Because the panel itself has to change in temperature to change the output--it is ONLY conduction that allows you to change output without changing panel temperature!

I really don't think that it is going to matter much if you design the cavity to enhance radiation--there is still a FIXED amount of heat that can be transferred at a given surface/air temperatures in the surroundings. Enhance radiation and you most likely just retard convection and vice-versa. To get more output you have to continually increase the temperature of the water.

Think now of what happens with a lot of bare-tube systems in cold weather... The boiler starts cycling on high limit before the space is adequatly heated. It's not because the boiler is too small. Nor is it because the water itself contains too few BTUs. It is not because the water is moving too slowly. It is because you have to FORCE those BTUs out with ever higher temperatures--a temperature that cannot be safely handled by the system!

In the early days of hydronic heating (particularly in England) there were systems using really small pipes with water at EXTREMELY high temperatures (read well above steam in the atmosphere). Consequently, they operated at EXTREME pressure and had to be assembled with the greatest care. Unfortunately they tended to explode!

imatellerslie

I don't think there's any doubt that

the black paint will help the tubing transfer heat to the underside of the subfloor, particularly with the reflective film below the tubing. I have no data to back this opinion up, but IMHO, it seems like a sure thing.

By the way, the color of the paint is irrelevant. White paint will work just as well if it improves the emissivity of the surface for infrared radiation. You want paint that is "black" to infrared. The color of the paint depends on how it reflects/absorbs visible light. Black paints absorb most visible light, and thus have a high emissivity to visible light. This doesn't necessarily imply that they will absorb infrared equally as well. White paints reflect most visible light, so they have a low emissivity for visible light. This doesn't necessarily imply that they will reflect infrared. That said, I think it is generally true that dark colored paint does tend to have a high emissivity to infrared as well as visible light, so black would probably work better, although its not a certainty.

imatellerslie

a couple of misconceptions

Mike,

I see a couple ideas here that need addressing.

"Conduction does not work the same way. Think of an electrical wire. It transmits almost exactly the energy REQUIRED by the load. It is not driven by a difference in temperature, it is driven by a difference in requirement!"


Current flows due to a difference in electrical potential (voltage); this is analogous to heat flowing due to a temperature difference. In face, the rate of heat transfered by conduction is exactly proportional to the temperature difference through which the heat is being transfered.

DaveGateway

Emit & Absorb IR

Mike T.
I think that I get your idea. That is: you can only get 100% thus if you raise the radiation by 2% then the convection portion must go down by 2%
Is that what you are getting at?
I think that that would be correct in a thermal equilibrium situation, but I don't think that this is.
Thanks for your wild & wacky ideas!
Bill Patrick

Mike T., Swampeast MO

The alternative is that increasing the radiation does not decrease the surface temperature of the tube, e.g. it increases conductive transfer from the water through the tube.

Considering I claimed just that in the same message, something is wrong--but which? both? neither?

Mike T., Swampeast MO

But doesn't it also flow at a rate (amperage) determined by the load?

imatellerslie

A motor draws current dependent on load because

its back emf will drop as load increases, allowing more current to flow. The line voltage is still "driving" current in the circuit. What would happen if line voltage was decreased? The motor wouldn't be able to provide as much torque or power output, because not as much current would flow.

For a purely resistive load, the amount of current drawn depends on the amount of resistance and the voltage (ohm's law). You can increase power output in that case by raising voltage or lowering resistance.

DaveGateway

Emit & Absorb IR

Hello, Mike T.

I don't see that the movement of heat from the water to the surface of the PEX as "THE" limiting factor or "bottle neck" here!

I think that we could increase radiation and not reduce convection!

I think "THE" limiting factor here, is the convection & radiation to the subfloor & then the conduction through the subfloor & surface material.

The same water temp & flow can give a much greater delta-T & thus move much more heat via conduction when the PEX is in contact with a heat transfer plate or embeded in concrete.

BTW I am in process of getting components to make up 120vac & 24vac LED indicators, for pumps, zone valves, end sws. etc.

regards Bill Patrick

jerry scharf

Sorry, I've been off the wall for a few days

This is not an area to carelessly toss ideas around. They last 150 years o physics has been largely involved in sorting these things out.

Thermodynamics is the measure of bulk heat problems. It was a huge step forward, and presented in a coherent form rules that governed many of the problems of the day. It worked great, but as people advanced problems started to show.

The most famous problem was that of solar spectrum. To get the right power from the sun, you came up with a temperature. Once you looked at the acual and predicted spectra of the sun, they didn't match up to predictions. The solution to this problem unwittingly launched the entire field of quantum mechanics. It's what you get when you stop looking at huge numbers of atoms at low temperatures. Nothing before that was wrong, just more limited in scope.

The solution was to say the electromagnetic energy (gamma rays through radio waves) had a dual nature as both wave and particle (not to be confused with the Huygens/Newton debate.) It rapidly became clear that at the infintessimal levels, lots of things that seems preposterous were indeed possible and happening. Theories kept leading to experiments that led to things like transistors.

Now we add something even stranger called DNA. It seems to violate the basics of thermodynamics and create more complex structures. This is also critical in understanding the total heat, since it can store energy in ways that thermodynamics won't allow.

This is the place we are in when it comes to measuring our overall energy container, called earth. Radiation in + energy release - energy stored = radiation out. When you have 200 million years between storage and release, you can see how it can have a real impact.

Physics has much more to learn, but even at this level the complexity is overwhelming when trying to look at an individual problem. It takes a careful understanding of the realm you're working with and then careful attention to details.

jerry

jerry scharf

now let's look at radiation coupling

Now it's time to start simplifying things. You have to choose a temperature, an emission spectrum for the tubing at that temperature and an absorption spectrum for the surface. You also have to choose a temperature for the walls and bottom of the staple up cavity and the emission spectrums at those temperatures. Most likely the walls will vary as a function of distance below the floor. Add the temperature, insulation values, MRT and convection flow of the top. Once you have all these, you now have the information to create a flow model. Then put in something for the loss out the bottom and ignore the sideways loss by assuming the adjacent bays are similarly heated and the joists have zero flow laterally. You can simplify some more by factoring out the above the floor part and put a static load on that. This is about as simple as it gets to do it using a combined heat transfer model. Other than spectral emissivity variation (which would be imperically measured,) you should be able to ignore the quantum effects.

Since you are trying to find the difference in a radiation component in the subfloor area, I don't see how you can simplify it much more than that. You have to look at the conduction, radiation and convection in the subfloor, all three will move energy.

Tim, you were talking about factoring in the angle. This is addressing the reduction in radiation density as a function of the angle and distance from the tube. Given the simple geometry, you can skip the FEA for this and look at the subtended angle.

Now comes my seat of the pants. Not knowing anything about the long wave IR characteristics, I've never felt warmer in any particular color of clothes in a unlit radiantly heated room. I've never heard anyone make such a comment. This would make me guess that the general effects may be low. Also, I don't know where you can get long IR emissivity spectra for paints, etc. All the things I have ever cared about stopped at about 5um wavelength.

Now that we've gone through all this, I wouldn't do the modelling at all. I'd build a few test bays like ME does, and play with paints.

jerry