BTU output of 1\" bare copper pipe

Mike T., Swampeast MO

They well understand emissivity...

The underside, nose cone wing leading edges, etc. are dull black to increase emissivity in the sections that are exposed to the most heat during re-entry. The upper portions are white and relatively shiny to reduce heat gain from the sun while in orbit.

D107

100K BTU per linear foot sound good?

I saw Dan's chart that I believe said 90K BTU per foot for 1" steel pipe; I figured copper was slightly more. Trying to finish a heat calc for the basement and I wanted to get the gain for 60ft of 1" pipe (180 deg supply temp) just below the ceiling. I know its high location probably de-rates it a bit, but I'd like to get a rough idea what you think. Half of this is supply and half is return on a monoflo system, so it might be less than 180 deg.

Thanks,

David

S Ebels

If I could find

If I could find my Burnham's Heating Helper I could tell you. They have heat loss from bare steel and copper for all kinds of temps listed in there.

S Ebels

Found it

Right in the bookcase where it belongs. I'm getting scary in my old age. Used to be I left all that stuff lying in heaps on the desk.

1" copper in 70* air with 180* degree water in it will give up 55btu's per lineal foot.

D107

Thanks--just saw Dan has copper chart too on Hot Tech Topics

Surprises me that 1" steel gives off 90 btus/ft to copper's 55. (I guess the 1" is inside measurement, so steel's outside measurement would be more than copper's.) So as a layman I'm thinking, steel is almost twice as radiant--why not use only that? Answer? Maybe hydronic systems work better when heat is more slowly released so the end of the line gets some?

Also interesting that just 3/4" copper if it was in a 2" baseboard/fins would give up at least 500btu per ft or more.

Also interesting that Dan calls the chart 'heat loss'--from the overall system--; in my situation it's a gain since the bare pipes will add needed heat to basement given the bare cement walls.

Thanks,

David

Brad White_9

Siggy's HDS has these figures

1" Type M Copper, 180 degree water in a 70 degree ambient: 65 BTUH per LF

Steel data is not available in the program. Too bad! I was curious.

When the ambient drops to 55 degrees the heat loss rises to 76 BTUH per LF.

[Deleted User]

Color of pipe has a lot to do with its ability to deliver heat..

Shiny copper "emmits" less heat than does dull copper or black iron pipe.

You're looking at it primarily from the convective input spectrum only. Paint the copper pipe flat black or elm leaf green and I'll bet it exceeds the output of black iron pipe, and that heat flow WILL go downwards, as compared to the convective output which will only go UPwards...

The biggest problem with attempting to use pipes as controlled heat emmiters is that you in fact have very little "control", and the control you do have rarely matches demand, so consequently, the space being conditioned by the pipes has a tendency to over heat.

I've actually put removeable insulation on steam mains passing through conditioned spaces and told the customer that if they get hot, put the insulation on, and if they get cold, take the insulation off. It is the ONLY way to truly control heat to avoid overshoot...

Maybe you should look into Danfoss' powered convectors and insulate the mains. In the words of Taco, "Do it right. Do it once"

ME

Brad White_9

Elm Leaf Green?

OK, Mark, I'll bite...

[Deleted User]

Well....

If the good Lord thought that felt black were a better absorber of solar radiation (emmisivity being the inverse of absorption) he would have made all the tree leaves black, instead of green right:-)

Actually, from WAY BACK, I had a professor of engineering (Dr. George Lof) tell me that elm leaf green ground to 1 micron thickness actually has a higher absorption rate than flat black by .01%.

We actually tested this in the labs up at Red Rocks and found that finned tube convector painted flat elm leaf green significantly increased the radiant out put in a closed, suspended environment.

S Ebels

Mark

You need to do a mind meld with Wikipedia and download all the info floating around in your noggin for the sake of posterior....I mean the rest of us... er, those of us who don't know that kind of stuff.

D107

Can't beat combo of humor and info at wall

so the more heat absorbed by paint, the more it emits, if I understand it. But that which is not emitted is not necessarily wasted, yes? Moves on to another convector, or back to boiler?

And what part of the convector did they paint? The supply pipe going through the fins? Seems like painting the shell wouldn't do much since it seems most heat travels through the vent as warmed air. Seems like a partial solution to areas of existing undersized radiation.

Thanks,

David

jp_2

WOW, expensive test equipment!

I would have liked to see an experimental set up that has testing accuracy down .01%? sounds more like they are equal if anything.

Jerry_15

Steel conducts more than copper? Give me strength. I do all my installations in platinum piping so I don't have to worry.

Bob Harper

emissivity

Mark is correct. Do a Google search on black body emmitters and emissivity. They have tons of calculations, coefficients, indices, etc. Also compare reflectivity with emissivity.

Other factors in this equation I would think would be the specific heat of the material, the mass of the material (thick vs. thin), time the heat is in contact, and as noted, the ambient temp. Note, too, you have discussed radiant heat off the pipe but there is some convective loss and conductive losses anywhere the pipe contacts anything including insulation. Then you have geometries of straight pipe versus fittings, valves, etc.. Then, too I suspect some bright guy has also calculated the differences in pipe internal surface area to mass flow, such as stagnant water in skinny pipes as opposed to pumping water through big pipes.

Could we say the Three T's-they aren't just for combustion anymore?

-A dryhead just babbling about nonsense. ;-)

Mike T., Swampeast MO

Yep, that's the strange thing about emissivity. The better a surface absorbs radiant energy the better it transmits it. AND any surface is always BOTH absorbing AND emitting. Whether it's a net absorber or a net emitter depends on the temperature difference between the surfaces. Those relatively higher in temperatures are net emitters; those relatively lower are net absorbers.

Mike T., Swampeast MO

Isn't elm leaf green very similar to copper verdigris? If I remember my studies properly, copper has the highest range of emissivity of any substance. From extremely low (when highly polished) to extremely high (when oxidized green).

Mike T., Swampeast MO

Thickness has no bearing on emissivity as it is a surface phenomenon.

When talking about heat output from pipes, horizontal vs. vertical orientation does have a significant effect. Horizontal has significantly more output. Vertical tends to retard natural convection. For the same reason, the more closely you space a gang horizontal pipes the lower the output. The spacing in those old "coil" radiators (gangs of pipes) was a compromise between output and compactness. The coils do however have greater output per square foot of surface area than any standing iron radiator.

hr

Store some copper tube in a room

with pool chemicals and you will soon see a FREE green coating appear Not sure if it is exaclty elm green, however.

hot rod

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D107

So how to reconcile chart that shows steel more emissive?

see hot tech topics charts under 'heat loss' from bare copper and steel pipe. A few posters on this thread seem to doubt steel's higher rate.

Mike T., Swampeast MO

I'm pretty sure that all has to do with the surface condition of the copper. When the copper is indoors and protected from the weather, it seems to take a VERY long time get to the "oxidized black" condition. I believe that's why "copper in service" is assumed to have somewhat lower emissivity (thus lower output) than steel.

If you're WANTING output from bare copper you can:

1) Leave out in the weather until nice and black.

2) Use chemicals to hasten the oxidation. Check stained glass suppliers--such chemicals are VERY commonly used to blacken stained glass assembled via the "copper foil" method. They work almost instantly.

3) You can paint the copper--preferrably flat. All paints have quite high emissivity but flat black and as ME mentioned, flat elm-like (say "dusty" medium green) are known for especially high emissivity.

BTW, special "low emissivity" paint is available. "Raydiance" is the trade name that I know. Rather expensive (compared to fine quality traditional paint); color selection is limited as it cannot be tinted; BUT physics and testing are behind it. Best use is in spaces where the walls are subject to high solar gain, e.g. a "sun room" where you want limit passive solar gain. Don't expect miracles, it [seems] to be a useful tool.

Jerry_15

How cool is that!!! But how exactly does one paint the inside of the pipe green? There's some guys trying to launch the next space shuttle anxiously awaiting this wisdom.

D107

which brings me to the black vs white umbrella argument

I had in India many years ago. I noticed that most Indians used black umbrellas which I found a strange thing to do at 110+ temperatures. I argued with my sitar teacher that they should be using white umbrellas which would absorb less heat.(Now that I think about it years later I'd guess that it was the fashion to use those big old black umbrellas for the rain and they simply used the same ones for the sun.)

My teacher, who was musically gifted but perhaps engineering-challenged, claimed that dark umbrellas should be used in the sun. He noted that the people who live in the hottest climates have the darkest skin. My layman's thought on that was that skin and umbrella fabric function differently. The skin has to have the ability to withstand that hot direct sun to protect the living person underneath--which darker skin with more melanin does. "Well," he said, "so must the umbrella protect the person underneath."

Of course most of the traditional men's clothing was white, perhaps for reasons having nothing to do with the heat...

Thanks,

David

Jerry_15

Much as I hate to keep this thread going I was out at a radiant job that has steel tubing (not pipe!) in the concrete. There were a trainload put in out here in the early 60's. It's painted green. I always assumed that it was a coating to protect the pipe from the concrete but...
Is this what the Stones were really talking about in Paint it Black? Of course we all knew they were laying a lot of pipe, but who'd have thunk it was engineered