Staple up Radiant

Mike T., Swampeast MO

Thanks jp. Didn't think I was <I>that</I> far off base although I must agree there doesn't seem to be much convective force in such a shallow cavity--particularly once the air reaches its' maximum temperature given the temp/size/etc. of the emitters in the given cavity.

When I did try to estimate the three forms of heat transfer in a bare-tube staple-up (tube attached firmly to the floor) there didn't seem nearly enough radiation and conduction to account for real-world outputs. The exception was oxidized copper attached with copper straps and at high temps which [seemed] to have some fairly significant radiation and conduction abilities.

<I>took something like 20yrs to prove Einsteins theory that very large object bent light rays, suggesting light has mass</I>

Try suggesting that light is really no different than IR radiation and that since energy transfer MUST occur both ways between objects that light must obey the same rule (even if it's not light transferring both ways). Then try suggesting that the reason that photons (of any sort) seem to have mass is that they are the embodiment of e=mc2 occurring between all separated bodies. Then try suggesting a definition of e=mc2 as "energy is mass that cannot currently be contained in the space which it occupies". Then put it all together suggesting that a portion of the mass of separated bodies can simultaneously be found in both and neither object. Then go even further by suggesting that this is a dual force (just like electro-magnetism) with the portion that seems to be in neither related to "energy" and the portion that seems to be in both related to gravity. You'll find yourself refuted mainly because accepting leads to the possibility of concepts that physicists have spent generations "proving" as "unscientific".

Adam_12

What is the benifit of having a 2 inch air gap between the staple up tubing and the insulation ?.Alot of differant answers and methods foil back ,bubble rap ,fiber glass batts ,plates ,no plates.This 2 inch air gap is very intriging and Iam sure we will get numerous schools of thought.

Mad Dog_2

I always believed it served as a \"wall\" of air space

that "kept" the heat going where it should be...a "curtain" to contain the heat. Mad Dog

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[Deleted User]

Three methods of heat transfer in staple up...

Conduction (very poor in this case due to a lack of surface contact)

Convection currents (also poor due to a lack of temperature differential air temperatues necessary to insure air movement)

Radiant (always prevelant, but dependent upon right angles to maximize heat transfer, and rectangular joist bays are not conducive to right angle transfers with round tubes...)

The need for the air gap is to insure that you don't eliminate two of the three critical methods of heat transfer, those two being radiant and convective.

Staple up in and of itself is a poor means of transfering heat. If you eliminate one, or two of those require means, the output suffers SEVERELY.

I've been called to jobs done by others, where they had the fluid temps maxed out at 180 degrees F and STILL couldn't maintain a reasonable temperature in side the home. Upon further investigation, it was found that although the joist bays had been insulated, they neglected to leave the required air gap. I sent in a crew, and had them pull the insulation down to create a good air gap, and VIOLA, they discovered the comfort of radiant floors!

Now then, theres the controversy about reflective surfaces. One of the major tube suppliers touts this as being "REQUIRED" in their literature, and in a perfect world, they probably have a valid requirement.

However, studies in the field suggest that if this reflective surface becomes covered with dust, and I guarantee you, it will, the spectral reflectivity of said reflective surface diminishes to the point that you're better off using the aluminum for beer cans, and not heat reflectance.

I do agree with the need for some sort of "barrier" instead of unfaced fiberglass, but I have proven in numeorus field cases, that the lack of an aluminum reflector has little to do with overall long term performance.

As for the bubble foil bubble stuff, we tested it in our labs at the college, and found it has an R value equal to that of 1/2" of sheet rock. There was no discernable difference between the bays insulated with BFB and the bay with NO insulation and 1/2" of sheet rock only.

It makes a GREAT stadium seat insulator to keep your butt from getting cold while watching atheletic games, but adds little benefit to resisting heat transfer, be it conductive, convective or radiantly in real space heating applications.

The BIGGEST problem with maintaining a 2" air gap is consistency. If you are the insualtor, you have 1/2 a chance of getting it close. You'll be fighting wires, potable water pipes, DWV running at all kinds of agnles, cross braces and so n and so forth.

If you depend upon foreign workers to do the insulation, they don't know about the required gap, and could care less. Theirs is not to wonder "Que", theirs is but to stuff or die....

But I can tell you this. If it doesn't get done right, and the system underperforms, guess who the HO and GC are going to come to ... You got it, YOU!!! Then you are charged with leveling and aiming the finger of blame...And usually, the fix would be easy if it weren't for all that darned finished sheet rock...

These are the many reasons I don't do staple up. That and the fact that in most cases it requires a substantially higher operating temperature. Not everyone can afford to do it right, and not everyone can afford the level of comfort and efficiency I have to offer. So be it. To each his own.


ME

Adam_12

Thank Mark more than a definative answer.It is good to get the right answer to often hydronic myths have a way of becoming preferred methods .I personally dont like staple up ,there too many outside factors that have a way of biting you in the ****.They install carpet or hardwood or someone puts a screw into the pipes.The least expensive method and the also the least effective.

hr

The term Staple Up seems to include

a lot of various methods these days. To my thinking staple up would be tubing stapled tightly to the underside of the subfloor.

Often times transfer plate, suspended tube or joist bay,UltraFin, and other products and methods get lumped into the "staple up" category.

Each has a different insulation detail.

With transfer plates the insulation can be installed against the plate, as this is a conduction transfer. Most all my plate jobs are now spray foamed against the plates and subfloor. A nice insulation detail to assure the rim joist get sealed for infiltration.

I really question the reflective ability of any insulation under staple up or suspended tube installation. If you ever get a chance to see that foil layer agter the home is completed, you would be surprised. All sorts of construction dust settles on the foil layer. Mostly the dust from sweeping up after the sheetrockers! I suspect the reflective layer has, in fact, very little to offer these systems, in reality.

Spend the money on increased R value instead. Too many warm ceilings below poorly insulated staple up and suspended tube systems.

Better yet use a transfer plate if it has to be installed from below. WarmBoard or others if it can be worked from the top.

hot rod

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jp_2

forget convection

my guess is that its conduction that's driving the heat transfer here. don't forget, air conducts and convects heat currents. conduction is not just for solids. remember the hot air furnace, not a convection process.

radiation is helping by heating the surfaces which in turn transfers heat to the air space.

Mike T., Swampeast MO

Huh?

Convection is a form of conduction, but in a non-solid environment it is occurring faster than can be explained by the conductivity of the materials involved.

Unlike solid-to-solid conduction however, it's exceptionally difficult to predict convection mathematically. Actual models are still used and even then it's difficult to separate convection from radiation.

Cooling of electronics and commercial food processing seem to be the most studied (and most accurate) convective processes.

When it comes to space heating I can find almost nothing regarding calculating natural convection in real-world operation of any heat emitter.

Since air is virtually transparent to radiation I though that a forced air furnace heated the air almost exclusively via forced convection.

jp_2

no, not really.....

.i see these as totally seperate.

convection is about fluids changing density; and gravity.
gravity being very important here. molecules moving.

conduction is about transfer of energies within a "material"(I changed solid to material), molecule to molescule,-bucket bragade. energy moving, molecules staying put.

I think you need to look in physics and thermodynamics books and not HVAC books to find these answers. specific answers may not jump out at you but they are in there. it may take a couple of years to figure it out though.

oh, in no way was I implying radiation in hot air furnaces???

what are you trying to calculate ? convection wise.

oh, one more thing; real easy to separate convection and radiation, work in a vacuum!

Wayco Wayne_2

I rarely staple up

anymore, but when I do I use a product called "thermopan" to make a definitive air space that the insulators cannot undo. Thermopan is a product made for inexpensive homes to enclose joist bays to make return air ducts. It's cardboard with a foil face on both sides. It comes in 2 sizes. One for 16 inch bays, and one for 24 inch bays. The down side is that it takes a lot of time to go back and make the air space with the thermopan,and time is money. I try to sell plates. Once the plates are up installing the tubing take very little time. I will try to send some pictures. WW

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kevin coppinger_4

as the Guiness boys....

say "BRILLANT !" Time is money...I again don't like plateless jobs. No room for error at -20F design...kpc

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Mike T., Swampeast MO

Where is there conduction in the HX-to-air heat transfer in a forced air furnace?

Specifically looking for a reasonable estimate of convective output from standing iron radiators under very low (say 5F to 20F) differential temperature conditions. Preferably with the radiator NOT installed in a location that tends to enhance convection (like on an outside wall underneath a window).

The convective models for heat sinks made up of vertical plates are sort of close, but those plates are heated from a solid bottom. With a standing iron rad, the "plates" are heated from within while the bottom is open.

I do try with physics and thermodynamic books but the translation from theory to reality often makes my head spin yet still leaves me questioning the simplicity of the "reality" models.

Physicists are an odd breed. They seem to have created a "religion" with towers just as tall and strong as the "real" religions that used to persecute them. The MIT debunking of the supposed "cold fusion" success is a wonderful example. By the time MIT admitted that their statistical analysis was flawed (even intentionally flawed), the inventors had lost all credibility in normal scientific circles.

jp_2

correction

yes you are right, anytime you use a fluid to transfer heat, by definition, its convection. so even in that little stale air space, 2" x 14.5" joist cavity heat transfer is convective. I was thinking mainly in the day to day sense of convecting air currents which doesn't seem realistic in the little joist cavity.

I agree physicists are odd, but aren't we all? we all make mistakes and often refuse to admit them until the end. sometimes you have to be stubborn, and sometimes you are right. took something like 20yrs to prove Einsteins theory that very large object bent light rays, suggesting light has mass. science doesn't come easy for me either, took 3 different text books to help me get throught chemistry and i quit at quantum mechcanics.

you might try the gas laws, pv=nrt to estimate air volumes and velocities for convection, you can measure temp differences. you'd certainly have to make assumptions and guesses. i think you could model the radiator as two round vertical tubes.

take a look at this site:
http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html#hph