Random thought on between joist hydronic...

kframe

The thread below about how to hang hydronic heating tubing when doing a retrofit install between joists got me thinking (I know, I shouldn't think...)

Has anyone ever tried painting the underside of the underlayment in the joist pocket black to absorb as much of the heat coming out of the tubes as possible?

Would it make much of a difference, or would it simply be wasted effort?

kframe

What?

NO one has any thoughts on this?

I'm shocked, shocked I tells ye!

Bob_19

Why Not

Just insulate the tubing to avoid any heat loss. But you idea does make alot of sense, you probably won't realize a great benefit from absorbtion in-comparison to conduction from direct contact.

Mike T., Swampeast MO

Will try to keep this short...

The only thing that the paint is going to change is the amount of heat in the form of RADIATION received by the panel. The factor it changes is emissivity--a very grey area of heat transfer to say the least. Remember this is NOT RADIATION TO THE HEATED SPACE BUT RADIATION TO THE PANEL THAT RADIATES TO THE SPACE!!!!!! BIG DIFFERENCE!!!!

http://www.infrared-thermography.com/material-1.htm

is one of MANY sources for emissivity values--note that in this study FLAT WHITE actually has a higher value than flat black! Notice also that most common building materials (with the notable exception of concrete) have fairly high emissivity in the .85 to .95 range.

To keep it as simple as possible a higher emissivity means more radiation is accepted with 1.0 being "perfect" and 0 meaning no radiation is accepted.

I spent MANY hours trying to find reference to a good model of radiation comparable to bare-tube, joist bay heating. The closest I could find was from a DEEP university class on commercial food processing.

I was trying to "prove" that radiation played a significant role in this form of heating and pretty much FAILED. What I wound up "proving" is that Ken Secor is NOT A QUACK WITH HIS SYSTEMS!

The MOST BY FAR I could even begin to assert was about 35% radiation. This was with weathered copper tube at HIGH temperature (190° or so). In this instance ANYTHING you can do to enhance radiation has potential. Most promising is a reflective layer underneath the tube (low emissivity below) and an radiation absorbing layer above (high emissivity).

With PEX though it becomes MUDDY--not grey. With copper it is quite fair to assume that the temperature of the tube will be VERY close to the temperature of the medium flowing through it--NOT SO WITH AN INSULATOR LIKE PEX! Radiation increases GREATLY with temperature difference between the radiating and absorbing surfaces. Radiant transfer to the panel in a bare-tube PEX system is most likely under 10%--possibly significantly less.

In this circumstance (bare-tube PEX) minor changes in emissivity at the panel will have INSIGNIFICANT effect.

Were I ever to try bare-tube joist bay heating I would use Ken's method--it's exacting and precise but has some true benefits when using a conventional boiler. He has and is more than willing to share the methods of his success but many/most will find it very difficult LEST THEY LEARN BY ROTE! My only reluctance would be using it under natural wood finish floors--particularly NEW natural wood finish floors.

Unknown

My curiosity is peaked

How can we get the details of Ken's Method ? I've been over to The Piers and find the new version of the website pretty confusing , and I'm not sure Ken posts there anymore .

Mike T., Swampeast MO

Where are you Ken?

You once thanked me for "proving" your contentions and I'm returning the compliment.

John T_2

Questioning minds

> The only thing that the paint is going to change

> is the amount of heat in the form of RADIATION

> received by the panel. The factor it changes is

> emissivity--a very grey area of heat transfer to

> say the least. Remember this is NOT RADIATION TO

> THE HEATED SPACE BUT RADIATION TO THE PANEL THAT

> RADIATES TO THE SPACE!!!!!! BIG

> DIFFERENCE!!!!

>

> http://www.infrared-thermography

> .com/material-1.htm

>

> is one of MANY sources for

> emissivity values--note that in this study FLAT

> WHITE actually has a higher value than flat

> black! Notice also that most common building

> materials (with the notable exception of

> concrete) have fairly high emissivity in the .85

> to .95 range.

>

> To keep it as simple as possible

> a higher emissivity means more radiation is

> accepted with 1.0 being "perfect" and 0 meaning

> no radiation is accepted.

>

> I spent MANY hours

> trying to find reference to a good model of

> radiation comparable to bare-tube, joist bay

> heating. The closest I could find was from a

> DEEP university class on commercial food

> processing.

>

> I was trying to "prove" that

> radiation played a significant role in this form

> of heating and pretty much FAILED. What I wound

> up "proving" is that Ken Secor is NOT A QUACK

> WITH HIS SYSTEMS!

>

> The MOST BY FAR I could even

> begin to assert was about 35% radiation. This

> was with weathered copper tube at HIGH

> temperature (190° or so). In this instance

> ANYTHING you can do to enhance radiation has

> potential. Most promising is a reflective layer

> underneath the tube (low emissivity below) and an

> radiation absorbing layer above (high

> emissivity).

>

> With PEX though it becomes

> MUDDY--not grey. With copper it is quite fair to

> assume that the temperature of the tube will be

> VERY close to the temperature of the medium

> flowing through it--NOT SO WITH AN INSULATOR LIKE

> PEX! Radiation increases GREATLY with

> temperature difference between the radiating and

> absorbing surfaces. Radiant transfer to the

> panel in a bare-tube PEX system is most likely

> under 10%--possibly significantly less.

>

> In

> this circumstance (bare-tube PEX) minor changes

> in emissivity at the panel will have

> INSIGNIFICANT effect.

>

> Were I ever to try

> bare-tube joist bay heating I would use Ken's

> method--it's exacting and precise but has some

> true benefits when using a conventional boiler.

> He has and is more than willing to share the

> methods of his success but many/most will find it

> very difficult LEST THEY LEARN BY ROTE! My only

> reluctance would be using it under natural wood

> finish floors--particularly NEW natural wood

> finish floors.








John Taylor

Custom Climate Systems, Inc.
Whitmore Lake, Michigan

hot_rod

How far do you want to go

to chace the ulitmate heat transfer. Certainly the copper tube gets up to temperature quicker. And I have measured about a 3-5 temperature difference in pex, from fluid to outside wall, and about 7-9 degrees on the heavy walled rubber.

Still not enough of a trade off to want to use all copper in a large job. The labor and cost diference doesn't buy enough benefit, in my opinion. Same with painting the joist bays.

I suppose if I were to consider joist bay heating for medium or high load areas, I'd look seriously at fin tube, as opposed to bare copper. You need surface area, if you want convection performance. From this standpoint the Ultra Fin product makes lot's of sense. Or a modified Slant Fin type element, running with the joist direction

You will still need much higher supply temperatures, however. Conduction transfer (plates in contact with the floor)is the best, by far. It beats convection and radiation combined, in this application.

hot rod

heatboy

I guess the old saying.........

you can't make a princess out of a pig would apply here. Save your brain ;-) and just use extruded plates and be done with it. You can dress a pig in a Gianni Versace evening gown, but it's still a pig.

hb

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

kframe

"You can dress a pig in a Gianni Versace evening gown, but it's still a pig."

I thought Hillary looked VERY nice in that gown at Bill's second inauguration...